2000 Outback- A/C compressor cycles off frequently.

[Stevo F]

At the start of the hot weather, I started up the air conditioning on the Outback I bought from my Dad last year and noticed that the A/C compressor would run for 30- 40 seconds, then cycle off for another 30 seconds, then repeat. I obtain an HVAC thermometer with a probe, that I inserted into the center dash AC vent. I found that when the compressor would run, it would get the air temperature down to about 48 degrees F, then the compressor kicks off and the temperature coming out of the ducts would rise to the upper 50's, then it would kick on again.

I had my mechanic hookup up his gauges to the A/C system and he found the refrigerant was 1/2 lb, low, so he added refrigerant and checked for leaks (he couldn't find any). I'm not sure when my father last had the A/C serviced (he doesn't recall). My mechanic said the compressor wasn't cycling so all seemed well.

When I drove it, I checked the air again, putting it on recirculate as you are supposed to with air conditioning, then it would cycle again 30- 40 seconds the same way, but when taking it off of recirculate, the compressor did stay on and kept the A/C temp at 53- 54 degrees, pretty cold, but not really as cold as it should be.

I rigged up the thermometer to measure the air temps as I drove the car 45 miles home from my Dad's (90 degrees and humid), and as I drove, if I kept the fan speed on 3 and didn't recirculate, keeping the temp around 53 degrees, the compressor never cycled, but if I dropped the fan speed to 2, or put it on recirculate, then air temp dropped to about 49 degrees and it started cycling on and off again.

So I have concluded that it seems like there is a switch that is switching off the compressor when the A/C temp drops (possibly to keep the evaporator from freezing up) but it seems to be shutting it off at too high of a temperature. Is there such a switch, and is there a way to test it see if it's functioning properly?

 

[mdconvert]

I'm not an expert by any means but trying to help. If there's a switch for "econ" or "econ mode", does turning that off help?

[el_freddo]

Seems about right to me. If the system is cooling properly it will shut off until gas temps rise again to trigger the AC pump on. 

Be glad you have good working AC on a 20+ year old vehicle! 

In saying all of that, I’m also no expert.

Cheers 

Bennie

[nvu]

It sounds like the low temp sensor is triggering.  Assuming the compressor is good and there's no blockage in your refrigerant system, next step is check if the evaporator coil clogged with debris. Maybe some leaves got in and is blocking airflow causing the thing to freeze over.

If it's making cold air consistently at max fan speed, likely just debris causing the evap to freeze over..

[Stevo F]

On 7/1/2024 at 2:38 PM, nvu said:

It sounds like the low temp sensor is triggering.  Assuming the compressor is good and there's no blockage in your refrigerant system, next step is check if the evaporator coil clogged with debris. Maybe some leaves got in and is blocking airflow causing the thing to freeze over.

If it's making cold air consistently at max fan speed, likely just debris causing the evap to freeze over..

On 7/1/2024 at 2:38 PM, nvu said:

It sounds like the low temp sensor is triggering.  Assuming the compressor is good and there's no blockage in your refrigerant system, next step is check if the evaporator coil clogged with debris. Maybe some leaves got in and is blocking airflow causing the thing to freeze over.

If it's making cold air consistently at max fan speed, likely just debris causing the evap to freeze over..

Thank you. Interestingly, If I drop the Dan speed the temp all starts dropping and that’s when the cycling starts. Has anybody tried the Subaru climate control cleaner that is sprayed through the drain hose into the evaporator to clean it out- does it work well?

Edited July 7 by Stevo F

[Stevo F]

On 7/1/2024 at 10:24 AM, el_freddo said:

Seems about right to me. If the system is cooling properly it will shut off until gas temps rise again to trigger the AC pump on. 

Be glad you have good working AC on a 20+ year old vehicle! 

In saying all of that, I’m also no expert.

Cheers 

Bennie

As a contrast, I checked my 2003 Forester which I would assume has a similar A/C system, and the A:C temp (on recirculate) got down to 44 degrees abs I ran it that way for at least 5 minutes with no cycling 

[Stevo F]

On 7/2/2024 at 10:43 PM, Stevo F said:

Has anybody tried the Subaru climate control cleaner that is sprayed through the drain hose into the evaporator to clean it out- does it work well?

[Rampage]

AC Compressor cycles when on recirculate.

On our 95 RHD Legacy Wagon the problem was caused by dirt, dust and small pieces of leaves collecting on the evaporator coil. They build up on the lower half blown there by the fan and held there by the moisture on the coil leaving the upper half clear. So, all the air goes through the upper half.
On the air output side of the evap coil is a thermistor located near the front upper corner. Sucking in the cooler air from inside the vehicle that air is made cooler and concentrated on the thermistor causing it to shut off power to the compressor. It does not shut off when using outside air because the air is warmer.

I had removed and cleaned the evap coil and the AC worked fine on recirculate.

It takes a lot of time to remove and clean the evap coil.