01 S80 a/c service mechanic said compressor cycling normal??

midimykeys · Post by **midimykeys** » 28 Jun 2014, 14:47

I took my S80 2.9 to get an a/c service. Previously I had tried to add/take out R134 to make the air in the cabin cooler. Only being able to add on the low side, I was certain I could not get an accurate amount in the system. After a few days with experimenting with R134 amounts, the compressor clutch started to engage and disengage every 15 seconds after the car a/c had been on for about 5 minutes (when the pressure had built up maybe). When disengaged, the air is cold, but it rises by about 5 degrees with a little humidity until it kicks in again. I gave up, so I took it to a local mechanic who evacuated the system, air, and oil. He said there was 2.8lbs of refrigerant in the system, and it should only have 2.17lbs. I was starting to freak out until he told me that I couldn't overfill the system because of high and low pressure sensors that were a part of the system. He refilled everything, and I drove away with pretty cold a/c. However, the compressor still cycles on and off every 15 seconds. I took it back, and he said that it should work itself out in a day or two, when the computer is used to the amounts of refrigerant. This seemed unlikely to me. Is there something else it could be? Did I ruin something overcharging it. It's bearable in the 95 degree heat, but I don't want the compressor or clutch to wear out because of incessant cycling.

Post by **jimmy57** » 28 Jun 2014, 15:55

You may have a dirty evaporator temp probe. The probe which sticks into side of evaporator case above and the right of accel pedal, can collect enough dirt and lint to offset the on-off temp points. Those probes also just fail.
That amount of cycling once fan speed comes down is not abnormal.
Unless you have a charging station that pumps refrigerant in then it is only added through low side.
You can certainly overcharge system to a point of harm but it does a high pressure sensor and would cut compressor off when pressure reaches 440psi. Pressure going over 400 but not high enough to kick off compressor can harm compressor so it is to be avoided.

midimykeys · Post by **midimykeys** » 29 Jun 2014, 01:31

Ok, I found the probe. How do I go about cleaning it? I have to try this before other, more expensive alternatives. I've searched and I can't seem to find anything relating to this in forums.

midimykeys · Post by **midimykeys** » 29 Jun 2014, 01:41

I cleaned it with compressed air, and re-inserted it. Still cycling.. 20 seconds on, 10 seconds off. I really don't want to kill the compressor or clutch.

midimykeys · Post by **midimykeys** » 29 Jun 2014, 01:43

Maybe I just need to try replacing the probe, but if you guys have anything else that would yield a cause for concern, I am ready for your expertise! Thanks.

Post by **jimmy57** » 29 Jun 2014, 11:01

It is normal. My 2004 V70 and the 99 S80 T6 I sold for my sister both sycled in that pattern once car was cooled down inside. Both have superb Texas a/c performance.

midimykeys · Post by **midimykeys** » 29 Jun 2014, 12:15

Did you ever notice the temperature rising a few degrees accompanied by a little humidity? It can't be right, because I've never been able to tell in other cars I've owned when the compressor was on or off, with the exception of hearing the sound if I was out of the cars.

Post by **jimmy57** » 29 Jun 2014, 14:12

In high humidity mine will fog briefly but I notice only a faint change in vent temps when it cycles off just before it comes back on.

midimykeys · Post by **midimykeys** » 30 Jun 2014, 12:19

Am I the only one to think the constant cycling is abnormal mixed with slight humidity and temp. change? Lee? <canyon-like echo> lol

Post by **jimmy57** » 30 Jun 2014, 12:39

Volvo put a lot of capacity into P2 a/c systems. Choosing expansion valve as control for refirgerant allowed for better idle cooling. As a result of the semi-overcapacity the system has a higher freeze risk for evaporator. Evpa temp sensing and cycling compressor to avert freezing is a normal function.
Do you turn down fan volume to reduce blower speed?
Have you checked and made sure the cabin filter is clean?

A new evap temp sensor might change it but it would be a gamble without a test to see if it is accurate. I will pull them out of case and let them sit for a few minutes and then check in VIDA to see what temp it shows and measure the temp where it is laying to see if the probe and my thermometer agree.