Air Conditioner & Heat Pump Troubleshooting FAQs

Lost cooling capacity
Weak cooling

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.

Our A/C unit has lost cooling capacity

I checked all of the basic things, changed filters, replaced thermostat, etc. We changed the compressor last year. The shut off valve seems to be okay. And, we replaced the attic fan last month. What could be the issue? - Anon

I live in an apartment complex and this weekend the air conditioner stop blowing cool air. I called maintenance and they came over to repair the problem.

He removed some plastic tube and drained water from it and said that was the problem. Two hours later it stops blowing cool air again.

Needless to say, I called them back over and he informed me that I would have to drain that tube (line) ever time it goes out or call them. Is this correct? Should I have to drain a tube (line) for my air conditioner to work properly? - WB

Reply by (mod) -

Anon: At DIAGNOSTIC GUIDE A/C or HEAT PUMP we list A/C problems that could be the issue - I'm afraid that if you've read through and been through all of those diagnostics and did not see something obvious such as a dirty filter or lost electrical power, then it's time to call in an expert HVAC technician to diagnose the problem and then to describe the repairs s/he recommends.

WB: I can only guess with so little info, but if your A/C system has a condensate pan that uses a condensate pan overflow safety switch, then that could be shutting your system down.

If the condensate pan stops draining - say from a clogged drain - the switch senses water accumulating in the pan and will turn off the system to avoid flooding the building.

Or it could be a different problem. It's time for your maintenance people to bring in someone who is qualified on air conditioning diagnosis and repair.

Why won't our Lennox cool our house below 82F?

We have a Lennox central air system and my house never cools lower then 82 even though are thermostat is set on 75!

Just had it refilled still no change what could be wrong Thank you mom of 4;) On 2011-06-09 2 by Tracy

by (mod) - Air Conditioner Can't Get the Temperature Down? Was the refrigerant leak fixed? Is the airflow blocked?

Tracy: if your A/C unit seems to run normally, and if the air coming out of the supply registers has good force and low temperature, then the unit may just be undersized for the home.

Be sure your air filter is clean (or replace it) and that there are no crimped ducts or closed air supply registers.

I take "just had it filled" to mean that someone has added refrigerant; but we don't know if anyone found and fixed the refrigerant leak. A/C systems don't "consume" refrigerant. If refrigerant level is low then there's a leak to be found and fixed.

Then ask your service technician to check the air temperature drop across the cooling coil; if that temperature drop is too low and the air flow rate across the coil is normal then there's a refrigerant leak or refrigerant metering or control problem to be found and fixed.

Upstairs A/C works but downstairs air isn't cool

I have a duplex that has both levels sharing one central air unit. The upper level is working perfect. The lower levels air is blowing fine but the air isnt cool at all. by AC

Reply by (mod) - no cool air on some floors

AC
I'd double check that ALL of the air conditioning is provided really by a single system and that your thermostat is set on COOL not FAN.

A/C keeps running but doesn't cool down enough indoors

I have the A/C thermometer inside set at 78 degrees. The temperature in the house is at 82 The unit continues to run but doesn't seem to cool enough to reduce the inside temp. I worry that it's running much too long. Help! Marty

Reply by (mod) -

Long running without cooling adequately could be due to many of the possible explanations we list in the article above;

Check the output air temperature at the cooling coil to be sure it's actually cooling, and if so, check for air flow restrictions like a dirty filter. If the system used to cool the building adequately under the same weather conditions, we tend not to suspect that it was under-sized and we look for an operating problem.

Mobile home wall unit not cool enough

Is there a general expected temp required for a wall unit? Mobile home has a wall unit but it seems that the output temp is only cool not cold. How can I determine if unit is working properly? On 2011-10-03 by Gary Johnson

Reply by (mod) -

Gary, see OPERATING TEMPERATURES HVAC

Outside compressor/condenser not running and no cool air inside

The AC unit runs but no cool air and no fan running outside, the unit is very hot to the touch.

My Main central Air unit outside is very hot and the fan is not running but still running, The smaller unit is still running fine. I have two because my house is very big 3600 SqFt. Do I need to get a new Central air unit? On 2011-08-26 by Thomas

by (mod) - Lost Cooling Capacity

Thomas I can't say you need a new unit before there has been an accurate diagnosis of the problem. When the outside compressor/condenser is not running you won't get cool air inside; but the problem could be a simple as a switch or control relay, or as serious and costly as a bad compressor.

Hot to touch sounds like a compressor motor that is not starting but I'm just guessing from so little info.

Under the LOST COOLING CAPACITY article (Found in INDEX to RELATED ARTICLES at our Continue reading suggestions at the end of this article) you'll see a link to

Compressor Diagnosis: Diagnose & Repair

I'd take a look at that info as well as calling an HVACR service company. Keep us posted.

A/C Runs but Cooling Capacity Isn't Enough FAQs

insufficient cooling

About a week ago we started noticing insufficient cooling of our 1000sq ft condo unit by our heat pump. We replaced a very dirty AC unit filter, and ran various checks as you recommended above. Later that same day, the temperature began steadily rising in our unit...the air was blowing but no cool air out of the vents at all.

We got opinions from two AC repair companies, both of whom said the compressor needed to be replaced.

Luckily, the part was under warranty (the unit is only appx 3 yrs old and we are the first to live in it). It took a good 48 hours or so for the place to become cool again after the work was complete.

And now, a week later, it still does not seem to be as cool as it should be.

Overnight, the temp drops as we want, but the AC seems to run all day. Tonight, for example, the thermostat has been set on 75 for the past 6 hours, the AC has not gone off in those 6 hours, and the thermostat still reads 79 degrees.

A thermometer in the vent reads 68 degrees. We are in central Texas, and the temperatures have been over 100 for 70+ days (110 today actually)...but I'm not sure that I should totally write this off as the reason for insufficient cooling. Am I just being paranoid, or should I assume there is still a problem? On 2011-08-28 by Sarah -

by (mod) - new compressor is not cooling as well as the old system

Sarah:

If your new compressor is not cooling as well as the old system did and the capacity was properly matched, I wonder if the refrigerant charge was correct?

A check of the air temperature drop ACROSS THE COOLING COIL should find between 15 and 22 degF.

If you're seeing that temperature drop at the coil the A/C system is operating normally in all other respects (no dirty blower fan, good airflow, etc), then it seems possible that the too-hot conditions in the home could be due to weather, house heat gain, and adequacy of the whole A/C system to start with

Switching Between Cooling & Heating Mode FAQs

Moved to SWITCH BETWEEN COOL & HEAT MODE FAQs

A/C Heat Pump Compressor / Condenser Unit Repair vs Replacement FAQs

Moved to REPAIR vs REPLACE COMPRESSOR / CONDENSER UNIT FAQs

Air Handler Blower Unit Repair vs Replace FAQs

Moved to REPAIR vs REPLACE AIR HANDLER BLOWER UNIT FAQs

Thermostatic Expansion Valve TEV TXV FAQs

Moved to THERMOSTATIC EXPANSION VALVE FAQs

A/C or Heat Pump Won't Start, Won't Run

Moved to

COMPRESSOR/CONDENSER WON'T START or WON'T RUN FAQs