2000 V70XC Cycling Cooling Fan (AC Related)

Post by **FlyingVolvo** » 22 Aug 2014, 10:41

Edit: I think the compressor is A-ok. Culprit seems to be the cooling fan relay causing temperature and AC PSI spikes. No Low fan means the pressure and heat build until the high fan comes on (which is what I hear), then turns off to below the threshold. The process repeats itself. Thinking back, the problem is much more common in hot weather too. More heat = fast cycling.

From today's weather warning: "HEAT INDEX VALUES... UP TO 110 DEGREES DUE TO A COMBINATION OF HIGH TEMPERATURES RANGING FROM 95 TO 100 DEGREES AND MODERATE LEVELS OF HUMIDITY."

Yeah, time to do something about this. A little background first: This issue has been occurring for a little over two years now and I simply haven't had the time to address it.

What happens: I start the engine, turn on AC and idle, the compressor will turn on, along with the cooling fan (small momentary dip in RPM). The AC blows cold, no issues there. Anywhere from 5 to 15 seconds later, I can hear the cooling fan stop, the compressor (Edit: maybe not) stops, AC blows warm for a couple seconds and then re-engages like normal (blows cold, fan turns on, dip in RPMs. It will do this constantly until I shut off the engine or start driving. This all is very noticeable in the city with stop & go slow driving. On the highway, the AC seems to work continuously with no interruptions. All in all, this makes it very difficult to cool the car in slower driving (about 2/3 of my commute).

Video:Having something visual to show always helps I think. I hooked up a freon filling nozzle that has a built in pressure gauge. (Edit: I think the compressor is okay, it's just the fan) I'm pretty sure the compressor cycles on and off because as I hear the cooling fan stop, the pressure begins to fluctuate back towards it's "off" PSI.

Listen for the cooling fan. Do my pressures seem right? Ambient temp during this video is around 100 degrees F.

Any thoughts? Freon pressure problem? Switch problem? Compressor problem?

Thanks in advance!

Post by **jblackburn** » 22 Aug 2014, 11:26

Your low-side pressure seems very high (it should be under 40 PSI @ 95 deg), even with a hot interior, and I believe your system is super overcharged.

With no high-side gauge/port to check, I am thinking that the hot-side/high-pressure switch is causing the compressor to disengage. On the highway, you've got constant airflow through the condensor at the front of the car, and it's able to keep the high-side pressure under whatever you need it to be to keep the compressor engaged (probably somewhere in the 300's).

You may want to consider completely evacuating the system and then charging by weight of refrigerant (it's listed on the fender of the car).

Post by **FlyingVolvo** » 22 Aug 2014, 13:37

Working with Justin's idea, I released a ton of pressure. With the engine on, AC on (recirculate) the pressure now fluctuates between 35 and 45 PSI (it's about 100+ degrees ambient right now). The pressure fluctuation corresponds directly with the cooling fan cycling on and off. While that continued to happen, I yanked one of the sensor wires going into the AC line and I heard a distinct *click* as the compressor shutoff and the pressure spiked back to 125-150.

So I'm pretty sure the compressor has been working, but the cooling fan cycles on and off every 5 seconds now. I think the blast of warm air is from the sudden lack of airflow at the radiator/condenser. Also, apparently there is a high and low speed for the fan? I only ever hear it at one speed.

What sort of things should I be checking with the fan? And anything else for the AC system?

Post by **FlyingVolvo** » 22 Aug 2014, 17:29

Did I do the fan relay test correctly? The wire is grounded and I just tested it on both pins as seen below:

Is this normal?

If someone can confirm this, I think I'm narrowing in on it. Digging through many old posts, it seems like AC pressure controls when the fan comes on and off. My fan seems to only work on high, so when it goes to "low" it's actually off, allowing the AC pressure to build up. The high fan kicks in again, fixes the heat and pressure issue, then turns off again.