A/C & Heat Pump Repair FAQs-3a

Q&A to Diagnose & Fix Air Conditioners & Heat Pumps
that won't start, won't stop, or won't cool or won't heat

A/C or Heat Pump Not Cooling the Building FAQs

New Carrier A/C system provides cool air but our house isn't cool

We just spent $5200 for a new 5 ton Carrier AC for 1900 square foot house in Phoenix, AZ that was built in 1951. The first day the system cooled the house down with no problem. The second day the unit would not cool the house below 84 degrees which is unacceptable.

The licensed AC contractor has been out the past three days trying to get the system to cool the house down, and has even replaced various parts. Today they they checked the air coming out of the vent and it is 59 degrees, but it is still note the house down below 82 degrees and the motor runs continuously.

The AC contractor has given up and said he doesn't why the new unit won't cool the house and why it never cycles off. His solution is for us just to watch it!

The unit they replaced never had a problem cooling the house down and now I feel like for $5200 I should have an AC unit that will cool the house. What do you think is going on? On 2016-07-31 by Karen

Reply by (mod) -

Karen

First, in very hot Arizona weather when the A/C has been off for a time it could take hours to cool down the building again.

When there is a good temperature drop across the coil (as I think you have since you say it's 82 indoors but the cool air supply is at 59 degrees) the A/C system is probably working.

I'd call the installing company, speak with the service manager or owner, and politely, ask that they send an experienced, senior service technician to the home to determine what's wrong.

I'd expect the tech to confirm that the system is cooling properly, has a good temperature drop across the cooling coil, and that the duct system is not blocked, leaky, disconnected, etc.

Certainly one would expect an installing company to warrant their work including its performance to normal standards.

But we have no idea what's wrong: high heat gain, air leaks, duct defects, improper duct layout or design, improper sizing of the AC unit, improper refrigerant charge, a fan problem or what.

Also see LOST COOLING CAPACITY for more diagnosis and repair suggestions.

A/C runs, blows cool air, but never reaches the thermostat set temperature

Air conditioning turns on,blows cool air, but never reaches desired temp...what could be going on? We havent turned on the heat in 7 yes.

.usually run the air conditioning for about a week in the summer...we turned it on bout a week ago..worked fine.

Shut off during the day..ran it at night to sleep..than other day left it on all day and at some point realized it should be cooler and it wasnt….check settings, breakers...nothing wrong..what to do? On 2015-07-06 by Melissa

by (mod) - AC never reaches desired temperature

Melissa you need an on site service technician. Possible causes are a refrigerant leak, ice-blocked coil, crimped or damaged ductwork or other causes.

At ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

you'll find an article titled LOST COOLING CAPACITY

that can help you diagnose the problem.

by Melissa

Thank you..at least I have some direction to go..I will give my husband this info!

Air Conditioner / Heat Pump Won't Stop FAQs

Also see the diagnostic help at

BLOWER FAN WONT STOP - THERMOSTAT SWITCH

FURNACE or A/C BLOWER FAN WONT STOP - be sure that you check that article for help in diagnosing a furnace fan or blower that doesn't stop running.

My Air Conditioner won't turn OFF - what to do?

Reply:

Carla if your A/C won't turn off it could be that the thermostat is set to a temperature that the system cannot reach - due to lost cooling or due to a setting below the capability of the system.

If your A/C won't turn off even if you set the thermostat to a temperature that is above the current room temp, then the thermostat or an A/C control board or switch is bad and needs replacement - in that case you need a service call from a trained HVAC Technician.

See OPERATING TEMPERATURES HVAC and

also CONTROLS & SWITCHES, A/C - HEAT PUMP

Question: our A/C unit keeps on cooling and won't shut off

For some reason, our dual zone unit keeps cooling the downstairs zone to well below the set temperature -- when set at 79, very cold air is still blowing though the thermostat reads 71. Cold air still blows even with both thermostats turned to "OFF."

Not sure what is causing this, but I am sure it's gonna cost me $700/month if I can't get the air to shut off.

Any thoughts would be greatly appreciated! - EL 6/25/12

Reply: when the indoor air handler for air conditioning won't stop check:

EL,

• check first for crossed or bad thermostat wires

If your A/C won't turn off even if you set the thermostat to a temperature that is above the current room temp, then the thermostat or an A/C control board or switch is bad and needs replacement - in that case you need a service call from a trained HVAC Technician.

Here are more diagnosis and repair procedures:

For air conditioners that "won't stop running" or "won't shut off" you will then want to see these articles:

• COOL OFF HEAT, THERMOSTAT SWITCH
• FROST BUILD-UP on AIR CONDITIONER COILS
• FAN, COMPRESSOR / CONDENSER UNIT
• HEAT WON'T TURN OFF - Stop Unwanted Heat

If the outside compressor/condenser unit stops running but the indoor air handler blower fan won't turn off, see

• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH

Also see 

• OPERATING TEMPERATURES HVAC
• CONTROLS & SWITCHES, A/C - HEAT PUMP

When my A/C is off I still Feel Cold Air Coming out of the Vents

Why when my air is off is there still cold air coming through the vents. In between cycles On 2016-03-17 by candy

Reply by (mod) -

Candy:

Don't get confused between the outdoor compressor/condenser unit and the indoor air handler unit operation. If the outdoor compressor/condenser unit stops but you still feel air coming out of your supply registers it's probable that the indoor air handler blower fan is still running.

That can happen, for example, if someone used a switch at the thermostat or at the fan limit control in the air handler to put the blower fan into continuous ON mode.

Check that the indoor air handler blower fan is really OFF.

See

• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH

If it is and you feel a draft at the supply registers I suspect that there is an opening in the ductwork OR air is circulating by convection through the system, entering at an air return register. If the problem is serious, ask your HVAC company about an automatic duct damper.

Question: My central air conditioner won't turn off

My central unit will not turn off. The temp in the house is 92 degrees and I have set the thermostat to 78, but it will not cool the house and will not turn off. Do I need to add freon in the unit?

Also, I flushed the unit with bleach to clean the pipes out and the air conditioner cooled the house for about 4 to 5 hours only. After that it will not turn off or cool the house. What can I do before calling a technican? Thanks - Ossie 6/8/11

Reply:

I'm not clear where you used bleach but it doesn't sound like a good idea.

Before calling a technician check your air filters and check for duct work damage, leaks, crushing, etc. See the article linked to at the ARTICLE INDEX the bottom of this article and

titled LOST COOLING CAPACITY for detailed diagnostic help for an air conditioner that is not working.

Question: My central air conditioner never shuts off

help,help. i have no problems with the air being cool. the unit will just not shut off unless i shut it off - Anon 7/3/11

Reply:

An A/C unit that is providing adequately cooled air at the supply registers but still won't shut off is either never satisfying the room thermostat or there is a problem with the thermostat or the control board. Or there's another problem we haven't thought of. I'd first check to see if the thermostat shows that the room temperature is at or below the set temperature. It it is, I'd call a service tech.

If the room temperature never reaches the set temperature then either the set temperature is lower than your system can deliver, or there is a problem to find and fix, such as a blocked air flow (dirty air filter or fan).

A/C or Heat Pump Won't Run at Night

A/C will run during the day but not at night

Why is it that my AC runs just fine during the day, but will not run at night? It's very hot outside, even at night.

Every night I wake up soaked with sweat, and I have to run the floor fan on me, just to try and keep cool.

This same thing happened when I lived in an apartment. I've tried to lower the temp, but then the thing will just keep running and running until I have to get up and turn it back up.

And no, it's not hot flashes. My husband gets hot too...(: 2016-06-01 by Kare

Reply by (mod) -

Since it's usually cooler at night, even if you kept your thermostat at the same setting day and night, the A/C system would have to work less hard at night, so if the problem were an inability to keep up with the cooling load that ought to be happening in the daytime.

But it's possible that a control that tries to run a defrost cycle (after a hard day's cooling work) is malfunctioning and so the system shuts down at the end of that hard work daytime cycle.

Your A/C system needs service. I suspect a control board problem.

 

Heat Pump / Aux Heat Insufficient to Heat the Building

Weak airflow in heating mode isn't giving enough heat

I've just moved into a house where there seems to be very little air flow from the ducted heating.

Heating only occurs for a short period and then cool air seems to flow out. I had a service technician come out and he said the compressor is getting too hot a tripping out.

He said that maybe there is a problem with air flow or pressures.

To me it's obvious that there is at least an air flow problem so after he left I climbed into the roof and found that the ducting pipework does basically a 180 degree turn around a truss brace.

The ducting there almost seems to have collapsed in on itself. To me it seems clear that this is most likely be restricting the air flow. Would this in turn be causing the compressor to trip out? On 2011-08-17 by Craig

by (mod) -

Craig

Provided that the air flow is weak in both heating and cooling mode, you will want to first check your filter, air handler and duct system for blockages, leaks, mistakes.

For that, see

DIRTY AIR FILTER PROBLEMS

and

DUCT SYSTEM DESIGN SIZE & DEFECTS - home

Heat pump can't keep up, aux heat is on, compressor is stuck in "defrost" mode.

My heat pump compressor is running but won't keep up indoor temp so aux heat is on. Compressor seems to be cycling to 'defrost' mode very often although there is no ice buildup.

Temps have been within the range that system normally maintains indoor temp with out aux heating. Thoughts plese? - On 2016-01-25 by BC

Reply by (mod): bad relay or control board?

If the outdoor unit is stuck in defrost mode I suspect a control board or relay failure. It's time to call for service.

If your AUX heat is insufficient to keep your building warm it may be that it's not working properly. For example, electric backup heat often contains multiple electric heating elements, some of which could be "off".

It's also possible that the outdoor temperature is high enough that the heat pump should be able to provide some indoor heat so not all the AUX heat is switched "on", but because it's stuck in "defrost" mode it's not providing that heat.

A/C or Heat Pump Runs but Doesn't Provide Cool Air FAQs

My A/C Unit Blows Warm Air, I'm doing some of the repair and it's not going well

My A/C unit is blowing warm air. The repairman added a pound of freon and recommended I add a stop leak additive to the system. I added it but the air still wasn't as cool as it should be. He came back out, said I had "low head pressure" and may need new TXV if adding more freon didn't help.

It didn't, so I called him out to replace the txv and he found the A-coil was extremely dirty. He cleaned it as well as he could with my vacuum and said He could cut it out, acid bathe it and reinstall for around $550 or I could try cleaning it myself with coil cleaner

I opted to try it myself. After he left, I noticed the condensor fan outside only runs for about 15 minutes then shuts off. I have to turn off the system and let it set for 30 minutes or so before trying again but it still shuts down.

With the thermostat set to 73 degrees, it's running closer to 80 (I had to buy a window unit to survive our 100 degree days). Any ideas? On 2015-07-20 by A/C issues-blowing warm air

Reply by (mod) -

A/C

I'm nervous about the prospect of the "stop leak" product clogging up the thermostatic expansion valve (TXV). Of course if it does clog up the valve then that's nice for the service company.

Watch out: if you're not trained on HVAC repair and if you don't have the proper charging equipment, there's risk that you contaminate the system and cause damage.

Followup by A/C - system was barely cooling - added refrigerant

Last summer, the system wasn't cooling. The repairman added 2 lbs of refrigerant and everything was okay. This summer, again, the system wasn't cooling. Serviceman came out, added a pound of refrigerant and said I should put in the AC Leak freeze because it shouldn't have lost a pound. I added it but am still having issues.

When I say "With the thermostat set to 73 degrees, it's running closer to 80..." I mean the thermostat registers 80 degrees. Sorry for the confusion. The coil is getting mildly cool as well as the outside line.

The system is barely cooling and the outside (condensor) fan runs for about 15 minutes then shuts off. It used to run as long as the inside blower was running. I'm not sure what else to try but I'm getting tired of paying the service guy $100+ every week with no change.

Reply by (mod) -

Now AC, continuing the diagnostic suggestion:

You say your system runs but is not producing cool air - "With the thermostat set to 73 degrees, it's running closer to 80 (I had to buy a window unit to survive our 100 degree days)."

If you mean that air delivered from the supply registers is at 80F then the system is not cooling. If the compressor is working and the refrigerant charge is correct you should feel cool or cold suction lines at the compressor and you should be able to measure a temperature drop across the evaporator (cooling) coil at the air handler.

If the cooling coil is not getting cold then most likely there is a problem with the charge or the refrigerant metering device.

See REFRIGERANT LEAK SEALANT USE

for a discussion of using leak sealants

Adding 2 lbs of refrigerant means your system was probably close to empty.

Even on a large system holding 5-8 pounds of refrigerant, that's still a pretty big leak. A pound a year is a big refrigerant leak for any A/C or heat pump system.

Normally a refrigeration system loses ZERO refrigerant. The charge is permanent unless there is a leak.

A dirty evaporator (cooling) coil will also reduce the cooling out put of a system because it blocks air flow. You may find the cooling coil also ices over because of the reduced air flow across it.

To distinguish between low refrigerant and a dirty coil (or dirty air filter or other duct defect) for the homeowner is relatively simple. If the air flow at your supply registers is weak I suspect one of the latter issues. If the air flow is strong but the air is not cool I suspect low refrigerant or a TEV that's not metering refrigerant properly.

At AIR CONDITIONER TEMPERATURE MEASUREMENT  we describe how to measure A/C temperatures for diagnostic purposes.

At AIR CONDITIONER TEMPERATURES we give typical A/C system temperatures you should find.

If your A/C system can't get the indoor temp below 80, unless you've got windows and doors open or some unusual heat gain situation, your A/C system is not working.

Watch out: If your system is leaking refrigerant as it seems to be from your description, especially where the leak is a significant one, you need to have a the leak point found and fixed. Don't just keep adding refrigerant: that's pouring your money as well as environmental contaminants into the atmosphere.

Followup by ac

The specs for my unit says unit charge is 7 pounds 3 ounces. The filter was slightly dirty but the coil was definitely clogged.

Once it was vacuumed off (still needs some cleaning) the air flow out of the vents increased quite a bit but it is still not cool air and doesn't explain the condensor fan stopping. The cooling coil is definitely not icing over-it barely gets cool and no windows or doors open.

Reply by (mod) -

The condensor fan runs or not under control of the compressor/condenser control board and switches. If the compressor is not running the condenser fan will stop. If the compressor fan is running without the fan then indeed a repair is needed.

If your system outdoor and indoor units run and blows out of supply vents but is only warm then no coolant is entering the cooling coil. That's a charge or a refrigerant metering device problem (most likely).

A service tech will check high and low side pressures and may need to adjust, clean or replace the thermostatic expansion valve if the charge is proper.