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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
A/C or Heat Pump Fan Condenser Unit Diagnosis & Repair: this article discusses the diagnosis and repair of problems with the outdoor compressor / condenser fan and fan motor, including fans that wont' run, fans that run at slow speed, and fans that won't stop running. Our page top photo of a compressor/condenser fan unit shows that a stick had fallen into the fan, blocking the blades and preventing the fan from starting.
A simple problem like this can also burn out a fan motor. Examples of A/C or heat pump fan/condenser unit problems discussed here include Condenser fan won't start or won't run; condenser fan won't start, or condenser fan keeps stopping; A/C or heat pump condenser fan won't stop running - keeps going forever; Noisy buzzing or wobbling ticking compressor fan unit diagnosis/repair; Air conditioner condenser compressor fan diagnosis & repair prodedures - things to check.
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This article series discusses the outdoor components of air conditioners and heat pumps: how the air conditioning compressor-condenser unit works; the detection of defects in air conditioning compressor and condensing units, including evaluation of air conditioner compressor noises, hard starting, lost cooling capacity, and detection of a burned out compressor or A/C compressors at or near end of their life.
See INSPECTION CHECKLIST - OUTDOOR UNIT for a simple checklist for the outdoor compressor/condenser unit. Initial, simple diagnostic checks of the air conditioning compressor are also described at Compressor failure diagnosis.
If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building.
The condenser unit fan is a blower that moves outdoor air across the condensing coil found in the outdoor compressor/condenser unit. The movement of outdoor air across the condensing coil transfers heat to outdoor air and allows high pressure/high temperature refrigerant inside the condensing coil to condense from a gas back to a liquid refrigerant.
The condenser fan is visible inside of the outdoor compressor/condenser unit such as the unit shown in our sketch at left, an in our other photos on this page. Our central A.C. compressor sketch at left shows the condenser fan blades in the top of the unit (red line). The green line marks a common location for the fan control circuitry, and the blue line marks the fan motor.
Other compressor units such as those used in SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS designs may mount the fan in a vertical position blowing out of the side of the compressor unit rather than out of the compressor top shown in our sketch.
If the condenser fan is running you will see the fan blade spinning at speed (typically at 1725 rpm) and you will feel air blowing out of the unit.
Watch out: as we explain at BURNED-OUT COMPRESSOR, if the condensing unit fan is not working the compressor itself may shut down or even be ruined by overpressure or over temperature.
If the compressor/condenser unit has power and the compressor motor appears to be able to start and run normally but the outdoor compressor/condenser fan itself won't turn on, the fan motor may be overheated or damaged - see MOTOR OVERLOAD RESET SWITCH.
Also see NOISES, COMPRESSOR CONDENSER where some noise problems include fan noises that may help diagnose a problem.
The air conditioner or heat pump condensing coil (shown at left) receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state. Sketch from Carson Dunlop Associates.
The Outdoor cooling fan (the subject of this article) moves outdoor air across the condensing coil to cool it and assist in condensing the high pressure, high temperature refrigerant gas back into a liquid.
All of the above-listed air conditioner or heat pump components are discussed in detail throughout this website using the links at the left of these pages.
Condenser fan won't start
Check that power is on to the outdoor unit and that the indoor thermostat is calling for cooling and set to cooling mode. If the compressor/condenser unit has power and the compressor motor appears to be able to start and run normally but the outdoor compressor/condenser fan itself won't turn on, the fan motor may be overheated or damaged - see MOTOR OVERLOAD RESET SWITCH.
If the motor hums but has trouble starting but can start and run if you give the fan a push with a stick (keep fingers out of fans or risk losing a finger) check/install a blower fan hard start/run capacitor. See CAPACITORS for HARD STARTING MOTORS
A condenser fan that won't start when power is turned on, but whose blades will spin easily when power is off may have a worn fan motor shaft bearing. You may detect this by noticing that you can wobble the fan motor shaft (when power is OFF) or you may notice that you can pull the shaft in and out of the motor (loose end-play).
Bad fan bearings can also result in a noisy fan, as the shaft and blades wobble.
Also see Blower Fan No Start / No Stop
Condenser fan runs only at unusually slow speed
Possible low voltage at the equipment; possible condenser unit control board circuit failure (See CONTROL CIRCUIT BOARD, A/C for details).
Also possibly there may be no power to the fan and fan blades are moving due to local breeze blowing through the unit. On occasion a "slow" outdoor fan may be due to a fan blade that is not secured to the fan motor shaft.
Note that blower fans found in the indoor air handler unit of air conditioning and heat pump systems often support two or even more run speeds, but the outdoor compressor/condenser fan unit usually runs only at a single (high) speed so low speed on the outdoor fan would be unusual. [Problems with the indoor A/C or furnace air handler fan are discussed separately atBLOWER FAN CONTINUOUS OPERATION and at BLOWER FAN OPERATION & TESTING]
A slow condenser fan (or air handler unit fan) could be caused by a bad start-run capacitor.
Unfortunately this condition could indicate a burned-out A/C or heat pump compressor motor. If the compressor won't start and if the unit trips a breaker or blows a fuse as soon as it tries to turn on, the motor is burned out and shorted. If the compressor/condenser unit is wired with 240V (or "220 volts") as most are, an overcurrent at compressor start-up may be tripping just one leg of a two-pole breaker or one of a pair of fuses, leaving the other circuit "live". This can leave the fan motor running.
A bad fan motor can also cause the fan to turn but only abnormally slowly. An internal short that is grounding the fan motor windings can leave the fan running, but abnormally slowly.
Condenser fan noises: ticking, buzzing, humming
Check for a fan blade hitting an obstruction in the unit; possible failing blower fan motor.
Condenser fan blades loose, wobbling, bent
Turn off power, visually inspect fan and fan blades: are blades cut, bent, or damaged? Is the fan blade assembly secured to the fan motor shaft? A bent condenser fan causes stress on the blower fan motor shaft and can destroy the motor. Minor bends can be corrected manually; damaged blades need to be replaced.
Condenser fan blades broken or come loose from the fan motor shaft
Turn off power and assure that the fan blade is secured to the fan motor shaft. If the fan spins on the motor shaft and the motor shaft won't turn the motor may be seized and need replacement. If the fan motor is OK one or more allen screws set into the center bushing of the blower fan itself may need to be tightened to secure the blower fan to the motor shaft.
Condenser fan won't start
If the condenser unit fan won't start at all, check for power to the unit and to the fan motor and that all of the controls are calling for cooling (or heat pump operation); check for loose, disconnected wires; Check for a frozen fan motor (motor won't turn manually when power is off). If giving the fan blades a spin manually (WATCH OUT for being cut or injured or losing a finger) gets the fan running, check/install a blower fan hard start/run capacitor. See CAPACITORS for HARD STARTING MOTORS.
Condenser fan runs but only intermittently and has trouble starting
Check for loose wires or loose components on the fan unit control circuit board.
Condenser fan won't stop running
A blower fan may run for a brief while after the compressor motor has stopped but if the outdoor fan never stops check for a problem with the control board wiring or circuit. Also see Blower Fan No Start / No Stop
Condenser fan motor buzzes or hums
If the fan itself is balanced and undamaged and secured to the shaft and the fan motor buzzes or hums the motor may be damaged, overheated, have an internal bearing failure, or the motor may be hard starting. Check/install a blower fan hard start/run capacitor. See CAPACITORS for HARD STARTING MOTORS
Condenser fan motor runs backwards
Could be a bad start-run capacitor (CAPACITORS for HARD STARTING MOTORS) or a bad control board. A detailed case of diagnosing and fixing a condenser fan that was running backwards at speed changes is discussed below at Questions & Answers about compressor/condenser unit fans.
At PRESSURE READINGS, COMPRESSOR we discuss other backwards-running electric motors including some types of air conditioner or heat pump compressors and even well pumps. Also see BLOWER FAN OPERATION & TESTING.
Condenser fan runs but keeps tripping its thermal overload switch and thus keeps shutting off. Typically this is caused by an internal short in the motor windings. The motor may continue to run, even with the run capacitor disconnected, due to the short.
We list this sequence of condenser fan troubleshooting checkpoints roughly in the order that an experienced service technician will try them, putting easy, cheap, or more likely causes higher in the list. Contact us if you have suggestions.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Which air conditioner, heat pump, or furnace fan is located where?
In our simple air conditioning (or heat pump) system sketch shown at left, the light blue fan shown at left in the sketch (above the red compressor box) is the outdoor compressor/condenser fan discussed at FAN, COMPRESSOR/CONDENSER UNIT.
The dark blue fan shown at right in the sketch is the indoor air handler or blower compartment or cooling coil fan found inside the building. This fan blows building air across the evaporator coil (or cooling coil) to cool and dehumidify indoor building air. We discuss this fan at FAN, AIR HANDLER BLOWER UNIT.
In a warm air heating system that does not include air conditioning as well, the indoor fan is still located in the indoor air handler and is discussed at FAN, AIR HANDLER BLOWER UNIT.
Question: what is the purpose of the condenser fan?
What is the purpose of the compressor fan and its fan blades? - Mike
Mike the reason you see a fan on the compressor/condenser unit comes from the need to transfer heat from the refrigerant system into outdoor air. Refrigerant gas is pumped from the indoor cooling coil through the outdoor compressor motor. The compressor produces high-temperature high pressure refrigerant gas.
Question: where can I find a video on how to install a FASCO condenser fan?
where can i find a install video for a fasco 1/6HP FLP1.3 230V 1075RPM Center AC unit - Richard 10/16/11
Richard, Fasco provides replacement and OEM electric motors including for HVAC equipment. You can contact Fasco directly through their website at: fasco [dot] com - you'll find that the company will be glad to assist you with installation manuals, guides,
Question: which way should air flow through my outdoor A/C or heat pump condenser unit?
From TC: Instead of blowing air out of the top my fan is sucking air in from the top and blowing it out of the side of the outdoor unit. I have 3 units same brands and 2 of them are blowing and 1 is sucking. I did have to replace the capacitor but I marked the wirers and pput them back the same. is this a problem?
Reply: most but not all A/C condenser units blow hot air in at their sides and out at their top.
TC, models of compressor/condenser units vary in which surfaces of the unit are air intake and air exhaust. As long as you don't block the intake and exhaust you'll be ok. But looking at your condenser unit design, typically you will see that outdoor air is drawn through the condensing coil first and then exhausted by the fan - the fan is usually "pulling" air through the coil not pushing it in that direction.
However, your fan motor could be running backwards. See "How can I diagnose and repair a condensing unit fan that is running backwards" Q&A below.
Question: How can I diagnose and repair a condensing unit fan that is running backwards
From Brent K: I have a Samsung Ductless 3 split A/C unit. The other day I noticed the condenser fan running backwards at a slow speed.
At the compressor/condenser unit, air should enter the cooling fins and drive out through the fan. When the condenser unit was first turned on the fan ran clockwise - in the right direction. But when the high speed kicked in the fan motor came to a stop then started to reverse direction. When the low speed kicked back in the fan motor came to a complete stop until the high speed kicked back in then it started turning in reverse again.
The cooling ability inside the house also diminished [as it would be if the compressor/condenser is having trouble cooling the refrigerant back to a liquid].
Basic fan motor diagnostics: I checked out the fan motor windings with an ohms meter. They didn't match what was published in the service manuel but there was an acceptable resistance level similar to other fan motors I have come across.
Next I looked at the run/start capacitor. The capacitor was a small black plastic block not one of those oval or round oil filled ones. I disconnected the leads after discharging the capacitor and checked it out with my multimeter set to capacitance. Sure enough the meter showed nil not the 4uf I was expecting. I called around to motor repair shops (HVAC shops sometimes give me a hard time and found a replacement 4uf 450VAC start/run capacitor for $11.00 CDN. Installed it and not the fan runs properly on low speed and high speed.
So my High School electrical training and 1 hour of diagnostic work saved me a bundle. If there had been a controller or refrigerant problem I would have called in a HVAC tech. - Brent K. 7/26/11
Question: AIr conditioner runs for a couple of hours then the condenser fan will suddenly stop
I have a nordyne model js3bd-030k that after been running for couple of hours the fan will suddenly stop even when you still feel the air circulating and out of the vents any body would know what is causing the fun to act this way any help will be greatly appreciated. thanks for any help
Mario, the air conditioner or heat pump diagnostics on this page apply to the outdoor fan found on the condensing unit. But as you are talking about stoppage of air coming out of your indoor supply registers, you will want to take a look at the diagnostic notes on the indoor air handler or blower fans (the indoor unit that circulates air in the building) - see BLOWER FAN OPERATION & TESTING.
Question: Compressor / Condenser fan stops working in hot weather - replacement motor also failed
I have an ongoing problem with my A/C unit. It is working until it gets very hot (over 100 degress here in Texas) and stop blow the cold air. I called a tech last year and he replaced the fan motor twice, once with a same model and next with a larger fan. Again this year I'm having the same problem. Any idea what could be teh soulation? - Abby
Abby I am having this problem and I can wait untill the late evening when the temp drops or the unit becomes shaded I can reset a swithch and it turns it back on and it will blow cool air untill the next day when it does the same again. I suspect it is the overheat switch because mine is always popped - Ernie
If a fan motor is replaced repeatedly I'd ask the service tech and service manager to do some further investigating as something else may be destroying the fan motor. Examples of other problems that can ruin the blower fan or condenser fan motor include:
Question: compressor condenser fan not working, compressor is humming, trips circuit breaker
come home to find the home hot and the condenser fan not working and the compressor making a humming noise. Took outside condensing fan off and got it freed up, oiled the bearings and it works, but the compressor is still not coming on. Whats Next? Thanks for your help. - Johnny
my A/c will run for 1/2 an hour them the home circuit breaker switch trips. A/C units seems to run properly until the CB trips. I've repeated this over several days 6 times. - George
Johnny, it sounds as if the problem is not the fan unit but the compressor motor itself is not starting. See COMPRESSOR & CONDENSING COIL, A/C where our diagnostics of that unit begin. A humming A/C compressor is unable to start; either the motor is ruined or you might just need a start/run capacitor.
George: as with Johnny's case, if your compressor unit is tripping the circuit breaker it's drawing excessive current. The motor may be running and may seem ok but drawing high amps. You need help from a service tech who will check for those conditions, or take a look at the same link we just suggested to Johnny, above. It sounds like a component is overheating; usually a tripping CB means a bad compressor motor or a control or problem causing the compressor (or another component) to draw high current.
Follow-up from Johnny:
put hard start on and it running again thanks for all your help - Johnny
Question: right motor for condenser fan
My compressor fan motor went bad. OEM was RPM 840/2SPD. The replacement was a 1075 RPM. Unit runs for about 30 minutes and shuts off. Could faster motor moving too many CFM be insufficiently cooling compressor and how?
Reply: swapping out a 2-speed motor for a 1-speed may leave control wiring incorrect at an indoor air handler - are you sure you're talking about a condenser unit fan?
Question: condenser unit fan startup troubleshooting - condenser fan starts slowly or stops completely
Ran into a very strange situation with my 3 ton HVAC heat pump. Capacitor, 240V relay both good. Windings on compressor and fan seem to be reasonable (Fan run winding 32.2 ohms, start winding 94.4, overall 125.9 ohms). Compressor run winding 1.3, start is 3.5 overall is 4.2 (expected sum of 4.8 ohm???).
When thermostat off, condenser fan runs. None of the windings are shorted to ground. When breaker is turned on, condenser fan starts up a little slower than normal then proceeds to full speed. When thermostat turned to cool, condenser fan quits and compressor turns on.
Pull one leg of compressor off and fan does not operate with thermostat on “off” or “cool” position. 24 volt ac to relay working correctly. Unit is 15 years old. Have you ever heard of similar situation ? - J.Y.
Reply: check the fan contactor, the circuit voltage and current draw when the compressor is starting; possible control board trouble?
I am sorry that I don't know an immediate fix to what you describe and no I haven't quite heard this sequence before. Some speculation and arm-waving might be of a little help though:
A condenser fan that won't stop running, won't start running, or acts weird, could also be due to a bad fan contactor switch - one that sticks on, off, or has burned contactors. And as we cited above, a fan motor that is overheating can be going off on thermal reset - those don't quite match your problem description however. But be sure that contactor switch is working ok and clean.
A slow condenser fan startup could be a bad start capacitor even though the one in place seems ok - it's cheap to try swapping in another cap, no? But you might want to look also for low voltage on the circuit. Shorts and lightning strikes and power surges can also sometimes cause symptoms like this (as can mis-wiring 240V or 3 phase circuits).
Regarding When thermostat turned to cool, condenser fan quits and compressor turns on. if you are seeing a big voltage drop ( is there hard starting compressor motor?) and if fan is fed off one leg of that circuit, I wonder if that might stop the fan. Does it ever re-start once the compressor gets going? Sometimes a motor will look good when tested "off" - with nothing spinning, but when parts move, a winding can open up or a connector fail.
My last arm-waving would be to wonder if the circuit board has been fouled-up.
Regarding: Pull one leg of compressor off and fan does not operate with thermostat on “off” or “cool” position. 24 volt ac to relay working correctly. - that makes sense if as often the case a 120V fan motor is being fed by one leg of the compressor 240V circuit.
I've posted this fan startup problem on the Compressor/Condenser Fan Diagnosis/Repair page - perhaps another reader will have some smarter troubleshooting advice for us. Keep me posted on what else you find - what we learn will help other readers.
Follow-Up from J.Y. - fan startup trouble traced to defrost circuit
Good morning, sir. Apparently this issue is caused from the defrost circuitry. It makes absolutely no sense to me at this point; however, when I take the black wire from the fan motor that goes to the relay (defrost circuitry, not the 240 volt relay) and put on L1 (120 Volt AC) the fan operates normally. This really has me confused because I see no way for L1 to ever get to the fan. L2 goes to one side of the normally closed relay (defrost). The only place that I can see L1 goes is to the compressor from the load side of the 240 volt relay.
Apparently when the defrost mode is on when heating in the winter, the condenser fan stops and compressor is running while the condenser is defrosting. While this makes sense, I was unaware of this. Once I found out that the condenser fan shuts off during the defrost mode (thanks to HVAC friend), I check the output and found L2 (which is what you would expect since L2 is on the other side of the relay from the black fan wire).
I am going to have to study the diagram further to understand how this works. Currently while I am happy to get the AC going, I am clueless to how L1 can ever get to the fan motor. Pulling the compressor wire also has an effect that I don't understand.
To help others if they ever see this:
On some heat pumps that use a defrost cycle, during that period the compressor runs and the fan turns off (the idea is to warm up the compressor). That would be normal operation.
If it's a properly operating defrost cycle on a heat pump, the fan might remain off and the compressor on for about 10 minutes.
If the system is operating strangely (leaving the fan on forever, or never turning the fan on - and other fan operation problems like a bad motor, contactor, capacitor, wire, etc are ruled out) then I suspect a bad control board.
But I'm confused about putting 220V on the fan circuit. Isn't your fan motor a 120V unit?
Question: could an improper dual run (start/run) capacitor cause the evaporator coil to frost or ice up?
A tech replaced the dual run capacator on the outside unit of my heat pump system. The fan would not spin and he needed help over the phone to get the unit running again. Could an improper installation of the dual run capacator cause frost and icing? Previous to his visit I never had a problem with frost or icing. - Mike 5/24/12
Mike, maybe in some way I don't fully understand. The fan on the outdoor comprressor/condenser cools the outdoor half of the system and thus permits condensing high pressure high temperature refrigerant back to a liquid form. One would think that if the refrigerant didn't condense back to a gas it would not be properly metered into the indoor cooling coil and I'd guess that the result would be reduced cooling, not more cooling or excessive cooling and icing at the coil.
Question: how would I know if the condenser fan motor is bad?
How wolud i if the fan motor of the condenser bad. I checked running caps and its good fan blade are good. - Johnny 4/11/12
If with power off the fan motor does not spin easily the motor or fan bearings are seized; but a motor could spin but not start if an internal winding has shorted or has opened.
Check to see if voltage is present at the fan motor wires. If voltage is present and if none of these steps will turn the blower fan on, and if you are certain that the motor starting capacitor is good (see CAPACITORS for HARD STARTING MOTORS), then we suspect that the motor may be seized.
If the fan blades spin but wobble, or if you can move the fan shaft up and down or back and forth where it emerges from the fan motor, then the fan bearings may be bad, causing wobbling and even binding of the motor assembly.
If the fan spins freely, there is no loose fan motor shaft play, and no fan wobble, checking the capacitor or even swapping in a new one is one fo the first repairs a tech will try as it's so easy and cheap.
On some fan motors that don't use an automatic-reset internal thermal overload control, there may be a ELECTRIC MOTOR OVERLOAD RESET SWITCH that has tripped off.
See VOLTAGE MEASUREMENT EQUIPMENT for a description of tools used to detect the presence of live electrical wires & devices and for the measurement of actual volts or amps - a step that you'll need to take with the motor out of the unit for testing.
Blower Fan No Start / No Stop - describes weird blower behavior can also be diagnosed and fixed - this article provides a detailed list of things to check.
Question: new condenser fan motor, cap, but compressor hums
Condenser fan motor, new, all capacitors, new, Works fine cools house for 1/2 hour then new fan motor shuts off and compresses hums, wait 1/2 hour and it does it all over again. help - Mike Nichols 5/2/12
my unit outside will not come on but it does inside what can be wrong - Larry 5/21/12
Mike it sounds as if you are describing a bad compressor motor, especially if you are dead certain the start/run caps are OK. See COMPRESSOR & CONDENSING COIL, A/C where we list diagnostic articles.
Larry: same advice as for Mike. If you are sure the controls are calling for the equipment to run and voltage is present, start by checking the diagnostic articles in the order listed at LOST COOLING CAPACITY.
Question: buzzing in the outside compressor/condenser unit
fan want run on aircndiction out side unit it just make a buzz sound - Joe Russell 5/23/12
Joe: could be a bad fan relay or start capacitor; Does the compressor try to start?
Question: confusion between indoor blower assembly fan and outdoor compressor/condenser fan
The blower will come on in the air handler in heat mode and in manual ,but not in auto ,what gives - Clyde 5/23/12
Clyde this page is about outdoor compressor-condenser units. Your question describes a problem with the indoor cooling coil and air handler assembly - at Related Topics above click on BLOWER FAN OPERATION & TESTING to read about that component and its troubleshooting. Could be a thermostat or relay problem.
Question: heat pump is not blowing cool air - the condenser fan won't keep running
have a heat pump not blowing cool air. The condensor fan will run for about 1 minute then shut off and not start again for a few mins. Once it starts up the same thing every time. This unit says it should be at 300 psig for both high and low pressure but when i put the gauges on it im only getting 155 on both sides. what could be causing this. I suspect that the unit has a low charge and is causing the fan to trip or the compressor may not be pumping, im not sure. all i know is that when my gauges are on it they do not change in pressure when i engage the contactor - Cox HVAC 5/26/12
Your system compressor is not continuing to run, nor is the fan. Check the start/run cap and the control board as well as the relay.
Question: the hvac tech left wires sticking up out of my fan unit
I just had a new fan motor installed....$569.98! Also is it standard procedure to have wires sticking up from the top,,,,? These were told to me to be so he could reverse the motor if need be? - Vicky Cummins 6/18/12
Vicky, no not in my opinion. It is a poor and dangerous practice to leave live electrical wires protruding out of any appliance - it's a shock and electrocution hazard. Perhaps the tech intended this as a temporary measure to be sure s/he could correct a wiring error. But electrical wires should not be left exposed.
Question: my compressor condenser is making a high squealing noise and the fan won't go on
I read all the above but I think I'm still confused. Last summer, I came home to hear my outdoor compressor unit making a high squeeling noise. I turned the AC off for the day and the noise never reappeared. Yesterday afternoon (temps in high 90's for several days)I lost air conditioning again. The outdoor compressor was making noise but the motor and fan were not running and it felt very hot to the touch. I turned off the AC and left it off till this morning. When I turned it on, I then went outside to check compressor. Fan wasn't turning so I took a stick and manually turned the fan blades. It then started up and continued to run for about an hour until the fan stopped turning again. I again turned the AC off for about an hour then turned it back on and the same result, fan would run for about an hour then stop spinning. Here's an observation: when the unit is off, I can take a stick and spin the blades freely in either direction. If you can help me I would appreciate it. Thanks - Don 6/21/12
We have a separate article on diagnosing compressor noises. I found it by searching InspectApedia for "squealing compressor" - the article is titled "HVAC Noise Diagnosis & Cure: How to Evaluate Air Conditioner / Heat Pump Compressor, Air Handler, Ductwork Noises", and you can find it by clicking on NOISE AIR CONDITIONER / HEAT PUMP in the links listed at Related Topics .
Question: cooling output starts and stops and no air is blowing out of our compressor/condenser unit
Our AC isn't providing consistent cool air. At start up, we get cool air for about 15 minutes, and then just regular air. This problem started when the temperature hit the upper 90's.
Al if your compressor fan is not running that is certainly a problem and the place to start. Check the diagnostic suggestions outlined in the article above.
Question: our compressor fan motor began to overheat
I have a heat pump, Its been running fine in 100 degree weather. Just recently the fan motor began to overheat and go off on overload. I replaced the fan motor and am still having the same issue. When the new fan first started, I thought "yeah", but i began to smell a heater smell coming from the top of the condensing unit. I'm not sure if the crankcase heater is on or not. What could be causing this? - Ethel 6/25/12
I'm not sure, Ethel, but you've made some excellent guesses. A fan motor that has a bad start/run capacitor may have trouble starting and may overheat the motor, as well as the other ideas you suggested. And a motor not properly mounted, or with a bearing that is binding, can also overheat. I think a savvy tech might also check for abnormal voltage level if everything else checks out ok.
Also check that the fan bearings are not binding, causing the motor to overheat.
Question: low side pressure was 120 and my high side pressure was 228 after a couple of minutes the compressor kicked on after 20 minutes the readings were 450 high side 78 low side
My compressor was running all morning outside temp was 114 around 3:30 my compressor stopped running at around 6:30 I installed my gauges the low side was 120 and my high side was 228 after a couple of minutes the compressor kicked on after 20 minutes the readings were 450 high side 78 low side my house began blowing cold air the unit is only 7 years old it's an American standard 3 ton do I have a freon problem or should I start testing start caps or what - Glenn in Las Vegas Nevada - 7/10/12
Glenn, also check for a bad refrigerant metering device; the compressor could have trouble starting against high head pressure; if leaving the system off until pressures equalizes fixes the "start" problem then I'd check or replace the start/run cap and then if problems persist, look for a bad or icing-up TEV. Incidentally I do NOT recommend just installing refrigeration test gauges right onto equipment without using a purge step in the same process, using the proper refrigerant gas; else you risk contaminating the system.
Question: erratic running compressor fan
I have an erratic running fan on my outdoor unit, fan not running, so replace ( Dual Cap) now fan ran like new or not at all, but the compressor motor still comes on. I checked the Dual start cap, and it check out ok once, but would fail the same test later. So I replace the capacitor (exact - OEM) and the compressor motor still came on, but not the fan. However, (the strange part) while thinking what was next, I lightly tapped on the top of the circuit board, in the area of the Fan relay ,and there others side by side, ( not for any reason ) just pondering. Then the fan started up and ran like new.
However, when the unit shut down, and restarts the fan may run great or not. When it does not, I go outside and lightly tap the top of the circuit board in location of the fan relay, the fan starts full speed, and I have cool air. This would make a little sense if it were a (mechanical relay), but its solid-state- no contacts there???? Go figure, maybe I need to troubleshoot the entire concert board, however everything is plug and play now days, and it is very unlikely I could get a component if I where to find it. I know a bit verbose, but I feel it could be so many things, so any suggestions would be appreciated.
Brian you've done some excellent diagnostics. Your description suggests that either there is a loose wire or an actual loose component on the circuit board in the compressor/condenser unit. Not only is having to tap on it not a reasonable way to live with air conditioning, it could be dangerous, risking a shock. If you can't see and fix a loose wire or connection to the board or to other wires nearby, I'd consider replacing the circuit board. In the article above where we list types of compressor/condenser fan problems we include this topic.
Question: compressor fan won't run unless I whack it with a stick
(June 12, 2012) Donn said:
My house A/C turns on OK. The outside fan will not rotate unless I stick a paint mixer stick between the vent holes and give the fan blades a shove. Then it cools fine. Is the fan worn out and has it become unable to start itself?
Donn: you describe a classic case of a bad start/run capacitor. See CAPACITORS for HARD STARTING MOTORS
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