Older Air Conditioner / Heat Pump FAQs

Fix Air Conditioners & Heat Pumps Set #5

Other A/C Diagnosis & Repair FAQs

What if my indoor unit has a higher BTU rating than my compressor?

What if my indoor unit has higher BTU than my compressor? i suspect the installer has fixed the wrong unit - 011-08-06 by Alan

Reply by (mod) - check with the manufacturer after getting the actual BTUh numbers

Alan, if the numbers are close the system may be adequately balanced;

I'd write down the data tag information from both the compressor/condenser unit and the air handler unit, then give the manufacturer's customer support line a call to ask their opinion.

Let us know the specifics of what you read on the data tags and what the manufacturer says.

Storm Damge to A/C & Heat Pump Systems FAQs

Storm damage to outdoor compressor/condenser unit

I have a PAyne 3.5 ton unit on my house. It was replaced about 3 years ago. LAst year we had a severe electrical storm and immediately after I noticed that the unit runs all day and does not cool well. A service tech says that everything looks fine but he replaced the compressor anyway and the unit began to cool better.

This year it has done the same thing after a storm but the company will not replace the compressor because the gauges show it is working.

How can this be? On 2011-07-25 by Dennis

by (mod) - start with proper and clear diagnostic tests

Dennis,

A number of problems could cause an air conditioner to not cool so well - low refrigerant for example.

If your tech replaced the compressor he would have had a reason, such as damage from the electrical storm, since that is quite an expensive repair.

Or the first time it was under warranty and profited the contractor but the second time it's not under warranty.

But you and I can't know that the two cases are identical with so little diagnostic data.

First it would be appropriate to correctly diagnose the cause of poor cooling - it could be something trivial like a dirty air filter, or it could be moisture or dirt interfering with a thermostatic expansion valve, or if the electrical storm actually damaged the equpment, perhaps a control circuit board.

by Dennis - It was storm damage

Sorry, i guess i wasn't clear. My unit was running and cooling well before we had a storm.

After the storm it is still running and cooling, but not as well. All the normal checks and issues have been checked and the tech even says the refrigerant and pressures show normal, the filters are new, coils are clean and remember almost immediately after the storm brownout it lost cooling power.

Even though the tech says everything looks fine (pressures, voltages, filters, coolant, etc) it is just not putting out air as cold as it was, showing about a 13 degree drop between inlet and outlet temperatures. The compressor is cycling but it just acts like it is not cooling enough. Anyway, thanks for the help.

by (mod) - rotation speeds of cooling fans, amperage draw of the compressor, and system refrigerant pressures

Dennis, did the diagnostic steps confirm rotation speeds of cooling fans, amperage draw of the compressor, and system refrigerant pressures? A bad capacitor or control board that causes a fan to run backwards or slowly could perhaps be involved.

Confirm that pressure readings mean that a compressor motor is bad

I have two heat pumps on the property that i work at. Outside air temp. has been about 95 degrees, The high side pressure is about 190 to 200 psig & the low side is about 110 to 120 or higher.

I have already replaced the compressor on another unit doing tha same thing.

Before i replace these two i just wanted a second opinion that it is the compressor that is going bad. On 2011-07-14 by PatrickBumgarner

by (mod) - check the TEV and other causes for abnormal refrigerant pressures before replacing a compressor motor

Patrick: I wouldn't replace a compressor unit just based on those pressure readings, as other controls could be at fault such as a thermostatic expansion valve;

also at very high outdoor temps the compressor/condenser may just not be keeping up. A diagnosis of bad A/C compressor would look not just at its output pressure but also the amps it's drawing.

Finally, high pressure on the LOW side after the compressor has been running for a while would certainly make it worth looking at that refrigerant metering device.

Outside condenser unit only runs for 15 minutes unless I turn it off to cool down

My outside unit turns on and will run for about 15 minutes and then stops.

I let it cool down for a while and it will work again but only for 15 minutes. I live in georgia and its been 100+ degrees here for a week or more. any info would be great On 2011-07-13 by mike

Reply by (mod) - "test" for an overheating compressor/condenser unit by wetting down that outside component with a garden hose,

Mike:

people "test" for an overheating compressor/condenser unit by wetting down that outside component with a garden hose, on the premise that the system is designed to be exposed to rainfall without damage. But if the unit is overheating I'd check for

- blockage of air flow by location too close to a building wall or fence or shrubs
- dirt or debris inside the condenser unit
- dust and debris on the condenser coil fins (big payback from keeping the coil clean)

and last and worst
- a failing, overheating compressor motor that is drawing high amps.

TN-Goose: specifying voltage levels and wiring for individual control circuit boards is, sorry to say, beyond my competence and scope of such a general discussion. Other than checking for normal voltage levels (120V or 240V or 24V depending on the component), more detailed control circuit analysis surely depends on the air conditioner model.

In my experience, (and what Hilliard taught at A/C school) most electrical problems on A/C systems are in compressors, relays, and overloads.

by dee

mike- sounds like compressor overload, most units can be replaced- the overload is generaly under 50 bucks.

by (mod) - electric motor overload switch that automatically shuts off the system

Thanks Dee.

Mike: Dee is referring to an electric motor overload switch that automatically shuts off the system - more often found on fan motors at the compressor/condenser unit or in the air handler blower compartment on that fan.

On many A/C compressors and some other electric motors such as well pumps, there is an internal overload switch that will reset itself automatically once the unit cools down.

A bad overload switch (if there is a replaceable unit) may be worth a try but more often in my experience if a motor keeps tripping on overload there is a more basic problem at work causing that overheating.

How to troubleshoot a contactor relay.

I was wrong about contactor. I used another (my father -in-law had identical replacement) and still had problem. I realized I should not have been checking the voltage to ground. I should have connected from one top connector to the other top connector (which both went to wire into the house).

That was 0 V -- so no connection -- due to a failing sensor that opened the loop.

I bypassed both sensors and when the "cool" turned on there was a 24V circuit and the contactor engaged.

The two sensors are hooked together with wires.

So I took them a part and tested each directly, both with my continuity checker and with by jumping (alligator clip connector) directly to the contactor. (I never disconnect the brown/common side of contactor).

The TEV sensor works. The other sensor (yellow wires) does not work. It is a sensor on the larger diameter refrigerant suction line.

Well I don't know if is a sensor problem or if the wires are bad or if the sensor is good and simply is doing its job. I am still trying to find information on this sensor. On 2011-07-09 by TN-Goose -

I googled and learned how to troubleshoot the contactor. However, it's still very strange why the condenser fan would run at about half-speed while the indoor thermostat is switched OFF. I checked the contactor while the fan is running and it is not closed (it clearly has a gap between the spring-loaded contact and the bottom portion, so the circuit is open).

However, the fan kicks into full speed when the indoor thermostat is switched ON (contactor plunger activates and closes the circuit), but a split-second later, the breaker would trip and shut-off the condenser/compressor unit. Maybe it's compressor seizing up, but what could be the reason for the fan to stay running at half-speed?

By the way, I disconnected the yellow control wire from the coil terminal, but the fan still ran at about half-speed. I guess that was expected since the indoor thermostat was switched OFF to begin with.

Didn't do anything weird; electrical connections are the same as it was before the troubles began. While the fan was running at about half-speed (with the indoor thermostat still switched OFF), I checked the voltage across the contactor with my multimeter.

One probe tip on the supply-power terminal, and the other on the terminal where the fan & compressor wires are connected. It read 126 VAC, however, the contactor was not closed (still floating up)!!! Somehow, power is being sent to the fan as if the contactor is closed. Also, I checked the resistance between the contactor's coil terminals, and it read 37.5 ohms.

Somewhere I read that if the resistance is significantly higher than 20 ohms across the coil terminals, the the contactor is OPEN and it should be replaced.

If the contactor is OPEN, how is it transmitting power to the fan?

Any thoughts on what could be the problem? Could it be related to wire damage in the coil of the contactor?

by (mod) -

Sounds more and more like a shorted wire or control board or control switch; be sure to check the voltage levels.