Yes it is supposed to be on all the time with the A/C.

 

Are you absolutely sure about that? Today I spent about 2 hours trying to troubleshoot this with a guy at the office. Conclusions:
- a/c relay behind the glove compartment is fine.
- a/c clutch is fine
- pressostat is fine
- pressostat electrical connector is fine

The fan is NOT always on. It seems to be responding only to engine temp, and not to the A/C.

We were able to reproduce several times a scenario where:
- the relay was coupled
- the car was idling at 1200 rpms instead of the normal 900. This isto compensate for the a/c compressor.
- engine fan is OFF
- compressor is OFF.

Since the car is idling at 1200 I understand that the ECU is receiving all the correct signals from the ECC and the pressure sensors, but for some reason the compressor is not working. After a while (compressor cools off????) the compressor engages and we get cold air. However the a/c fan is still not turning on. I will check the wiring diagrams to try to understand the problem.

I am trying not to take it back to the guy who did all the work on the A/C because he told me the first time that he had worked on the relay wiring and we found the relay in original shape, so he probably ripped me off for the first visit which was 50 USD.

 

Yes I am sure the fan is supposed to be on.

 

I took the car to a shop to have the A/C high and low pressure lines measured. We only found a service valve on the low pressure line. Where is the high pressure service valve?

 

There is no service port for the high pressure.

 

So how do I measure the pressure on the high pressure side to know if there is a pressure problem? Do the shop need to have the special Volvo a/c machines or can it be done with a generic one?

 

They need a really good scanner that can read REAL TIME for everything in the ECM.

 

I guess it's time for a trip to the Volvo rapership to get this correctly diagnosed.

 

I had the same problem in my 1996 850 R and bought the recharge kit with gauge cost$33.00 and whatI needed to do is drive it for awhile pull over hook up the r134a kit and keep charging till it stayed cool olny took about 45 min total to get the ac perfect mater of fact had to turnit down on the way home it was so cold.


rick

 

How do you bypass the sensor on the back of the compressor? What does it look like?

 

The sensor plugs inline you would unplung the sensor and plug the wires together.

 

After two years of no A/C in the 850, my wife will not even travel with me in the Volvo during summer. I asked the A/C guy if I could do the work with him and he accepted, so I spent 3 hours at his shop on Friday and 2 hours yesterday.

The problem was either low freon (leaking evap) or electrical problem with the cooling fan. Compressor clutch had been fixed and pressostat replaced during 2007.

First we checked the fan relay. The circuit takes 12V directly from the battery and it has two floating ground pins, which are used to select low and high fan speed. We manually grounded each pin to the manifold, the relay worked fine and the fan spun at low and high speed. We left it spinning for a while to see if the relay would detach, but it was fine. That rules out problems with the fan relay.

The ECU is not sending the ground signal for some reason. Probably the high pressure switch is bad, but since I am not willing to spend USD 300 for a new switch just to try it out we did the following mod. The A/C guy pulled a wire from the low pressure switch output. He added an auxiliary relay beside the big cooling fan relay. Instead of using the ground signal from the ECU to couple the fan relay, we have taken the positive signal from the pressostat, passed it through the aux relay, and connected that output to the fan relay low speed ground input. The fan is spinning at low speed whenever the compressor is on.

We checked the high pressure switch wiring and there was some getto connection there from a previous owner. Luckily the A/C guy is now part of the Bosch franchise, so he has original Bosch plugs which we installed to replace the getto cables and broken plugs (no metal release tab). Same thing for the pressostat. We replaced the plug on the wiring side. All the connections were soldered, not just taped together.

We then vaccumed the freon, filled it with nitrogen and did a high pressure leak test. He has a probe that senses freon and nitrogen, and he used that to see if the system was leaking. Everything is fine apparently.

Goodbye nitrogen, hello R134a, pressure is ok and so is the fan. A laser gun measured 5.3C at the vent, so the air is cold enough. He also cleared any DTCs and the service light for free. All this for USD 130.

The compressor is still disengaging at stop lights after about an hour of driving. In movement the A/C works fine now. It used to cycle very quickly before.

Is pressure too high on the high side? Maybe low speed fan is not fast enough to help the condensor?

I´d appreciate Tech´s input on this.

Thanks
Axel

 

I would have to say that Yes it is very possible that the Low fan speed is not enough to keep the system working properly.
If you can try to have it just swap the wire and make it run at High fan speed when the A/C is on.

 

Would it be ok to leave it in high speed? I suppose it would not damage the fan, but it would definitely eat more current from the battery and the noise in the cabin would be noticeable.

What do you think, Tech?

 

OEM they are setup to run on high speed when the A/C is on.

 

Great info, I didn´t know that. I supposed they started out in low and when the pressure got higher the ECU switched the fan to high to get more air through the condenser.

At least that´s what I would have coded if it were my software.

 

I think it just always runs on high speed.

 

My A/C is already modded, so I can´t test how it works OEM. Maybe someone else can run some tests and post results here.

 

Mine runs on high speed with the A/C on. It always kicks on high when I turn the A/C on.

 

I´ll change my mod from low speed to high speed tomorrow. Let´s see if that helps. Thanks Tech