HVAC Compressor / Condenser Fan Diagnostic FAQs

Q&A on how to Diagnose & Fix the Condenser Unit Fan

Common Condenser Unit Fan Diagnostic Questions & Answers

What caused damagee to the fan blades on my condenser unit fan ?

My condenser fan is a trane fan 03652 or replacement fan 04690.

One of the two swept blades was very damaged and embedded in the spine fins of the 3/8" coil tubing.

The coil was not penetrated & maintains pressure. Upon testing the condenser motor, it runs and spins true.

The only culprit I could pin this to was that the framing the motor & fan are supported by, was that of the four screws that secure this assy to the chassis, 3 of 4 had missing spacers.

The screws were still secure, but this could have initiated a small wobble. This is speculative.

The four screws of the fan motor to support frame were still tight, as were the four bigger screws attaching the framing to chassis (minus spacers).

Am I barking up the wrong tree and should I be looking elsewhere? 2020-08-03 by Wayne

Mod reply:

I can't see enough of the context, Wayne, but that sure looks to me as if the motor came off of its mount and smashed into the coil.

Now that you've removed the whole motor assembly we can't see details that would explain what happened.

Perhaps you can recall the condition of the fan motor mounts when you began to disassemble your unit.

Is the problem with the fan motor or the compressor motor in my condenser unit?

I've a Lennox outside a/c unit.

The fan/motor and compressor are part of the unit.

The fan was not spinning and the A/C is not running. I've isolated the problem down to the fan/motor or the compressor, but don't know how to check or find out which it is. Any idea on how to check if the fan/motor is 'bad' or the compressor is 'bad'? - Fan or ... 7/23/11

Reply:

Fan or compressor: you could also have a bad control board, or relay switch in the compressor/condenser unit.

If the fan is bad and the compressor is OK you'll hear the compressor turn on at the start of a cooling cycle, though a bad fan and system overheating could later cause some compressors to turn themselves back off.

Similarly, if the compressor is bad your fan motor would still run. So I'm suspecting a control or switch problem.

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

Reply:

Johnny,

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.

New coleman control board keeps cutting off the fan

i bought a new coleman control board for my heat pump in the fan is only running for 3 min than cut off. 2016-09-14 by deena edwards

Reply:

Deena

One can but guess that as the control board is new and guessing that the fan relay is on the control board the trouble is elsewhere. I expect your service tech will check voltage, loose wiring, fan motor start/run cap, fan bearings.

Follow up:

I straight wired it in it runs good

Reply:

Good diagnostic - especially if nobody gets fried.

That suggests a bad fan control, relay, or control/relay wiring.

What is the purpose of the outdoor condenser unit fan?

What is the purpose of the compressor fan and its fan blades? - Mike

Reply:

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.

That gas then flows into the outdoor condensing coil - it looks sort of like a car radiator with finned tubing. As the hot gas flows through the condensing coil, the outdoor FAN blows outdoor air across the hot condensing coil

That cools the gases inside the coil back to a liquid state and at the same time is transferring heat into the outdoor air.

The liquid state refrigerant can then return to the cooling/evaporator coil back indoors in the air handler where it is used to cool indoor air.

The "magic" of an air conditioner or heat pump is that by INCREASING the temperature of the refrigerant gas to a high level outdoors we are able to move heat INTO outdoor air even when the outdoor air is warmer than the indoors of the building.

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

Reply:

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: air conditioning drags voltage

The Air conditioning drags voltage and almost turns off other appliances when compressor attempts to start up.

And if used on a generating set it seems to power off the generating set, though testing the compressor with a digital multimeter it seems it's still functional, or I suppose so
Please advice on what to do, thank you 2020-06-04 by Nsisong

Reply:

Nsis

Usually drawing high amps is a sign of a failing motor

What is causing humming at the condenser unit fan motor?

Changed compressor starter capacitor but not the dual run capacitor. Now the compressor comes on (freon line gets cold) however; the condenser fan is not running but humming.

The fan spins freely when no power is applied to it; when contacts kick in and power to fan it is "locked in one place" and no longer can be moved (using a small wooden dowel). I ohmed the 3 motor windings and they add up correctly.

Could this just be the run capacitor? Is this more likely the fan bearings? 2020-06-11 by Fred

Reply:

Humming fan motor usually means either a bad starting cap or a seized motor.

First see our advice at CAPACITORS for HARD STARTING MOTORS

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 "Steps to diagnose and repair a condensing unit fan that is running backwards" just below.

Steps to 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.

The controller card [circuit board] checked out OK

with 220V on the pin for low speed and when the condenser coils heated up the high speed kicked in and the high speed pin had 220V there. Good I thought the controller is working.

Next I looked at the run/start capacitor - found a bad motor 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

How do I choose the right replacement motor for a condenser unit 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?

LD Neal

OEM was RPM 840/2SPD looks like a two-speed fan motor; if you replaced it with a single speed unit, and IF the original wiring was using two speeds, the new fan would indeed be acting differently.

But you are describing the condensing unit fan. More air providing more cooling at the condensing coil would be an improvement in system efficiency and I'm not aware of a case where it would be a cause of insufficient cooling.

Unless ... it's not wired properly; if the fan is not running when it should, the result would be lower system efficiency and even risks compressor damage.

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

Reply:

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.

Usually an iced evaporator coil (cooling coil) results from

• slower air flow across the indoor coil because of a dirty air filter or fan unit or an indoor blower fan that is not working properly
• a problem with the refrigerant metering device (TEV)
• low but not zero refrigerant in the system

In the link at the ARTICLE INDEX the bottom of this article under COOLING COIL or EVAPORATOR COIL see the

article FROST BUILD-UP on AIR CONDITIONER COILS

 

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

Reply:

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.

AC unit stopped putting out cold air - is there a reset switch?

After returning from vacation where we turned off the ac, (and water)when we turned the ac back on one of the two units, stopped putting out cold air. after going thru this awesome website, i may have found the problem.

The condenser fan outside does not come on, so i used a stick to make it run, and it did ! thought i fixed it. but the fan speed was slow compared to the other unit and the air coming out was not warm like the other unit - and then within a few minutes the fan turned off again.

The fan motor is a Emerson - Part # 37L7401 - if it has a reset switch then i will try to figure out how to get to it ( i am not very handy - not sure how to remove the cover to get to the fan) - do you know if this motor has a reset switch ? The other thing i learned from the website, is that the problem could be the capacitor, not sure how to replace that, but will cross that bridge if neccessary.

If you could please give your opinion on what is the most likely fix for this problem i would greatly appreciate it. thank you. Again this website is awesome ! (July 15, 2012) Sean said:

Reply:

Sean if the fan spins freely with power off but won't start and run on it's own the first thing most techs will do is swap in a new start/run capacitor. It's worth a try. If you're not familiar with electrical wiring, as it can be dangerous, even fatal, I'd hire a professional.

 

Cold weather problems at the compressor/condenser

The temp outside today is 0, and though I hear the fan in the furnace running, and air is coming out of the registers but there is no heat. I check on the heat pump and there is ice all around the base (from concrete onto bottom of pump). Perhaps the fan blade is frozen?

Should I pour hot water on it? Does it, as you have stated in one of your responses, have a defrost cycle and I should check in a quarter hour if it is running again?
(Nov 27, 2012) Rob Munn

Reply:

Rob,
At such low outside temperature I'd expect your heat pump system to have switched to backup heat mode. Is your backup heat not working?

 

Question: compressor/condenser trips circuit breaker

My 4 ton Bryant unit does both AC and heating.

One of the two side by side breakers indoor often trips - I think the tripped one controls the outdoor unit because the fan for indoor air circulating still runs. I reset the tripped breaker, and it goes for another day or two, then trips again. What kind of problem is that?

Reply:

Gary,
Breaker trips in response to an overcurrent. A shorting wire, relay, or control can cause the problem, but more common is a failing compressor motor that is hard starting, thus drawing high current a startup. Ask for help from a service tech. S/he might try a hard start capacitor kit to see if that buys some time.

Fan blades actually ripped off their mount

What would cause the fan blades to actually rip of their mount two ripped off and the unit was vibrating a lot. It has done some damage on the inside walls will this have to be replaced too. - (Mar 2, 2014) Bill

Reply:

Bill:

A loose fan mount or a bad fan bearing could do what you describe.

Also check the voltage level

 

Compressor outside your home supposed to run when you turn the heat on?

Does the compressor outside your home supposed to run when you turn the heat on - (Nov 10, 2015) Cc said:

Reply:

Yes, if it is a heat pump and if the outdoor temperature is not too low.

Not If your compressor condenser unit is only supporting air conditioning.

Not if the outdoor temperature is so low that your heat pump cannot operate. Then you will be on back up heat.