850 Aircon Servicing / Faultfinding

[850_olaf_nz]

Hey! I knew the A/C wasn't blowing cold when I bought the car. Took it to an A/C specialist today. He's done a bit of poking and prodding.

Here's the intitial help I need:

We found the "low side" check valve just behind the headlight on the RH side (looking forward). Couldn't find the "high side" check valve! Can somebody describe *where* the high-pressure check valve is for the A/C system on my 1997 850-T5, please?

It was "one sided" diagnosis. We pumped in some gas to the low side, and now the compressor starts up when we switch on the A/C. It switches off again within about 4 seconds, then switches on again 6-10secs later.... he notes a nice cold pipe going in through the firewall to the evaporator...

So going forward, the suggestion is:

1. Loacte the "high side" check valve!

2. full vacuum out of the system, and refill with 800grams of r134a.

3. Test.

.... if the system's not blowing cold, look in to what's going on in the cabin under the dash with the evaporator.

So, HELP - where's that damned valve hidden? And if you've struck these symptoms before, what was the exact fix?

Thanks in advance.

'olaf'

[850_olaf_nz]

Anyone?

I could really use that key info - where to find the high-side A/C check valve.

thanks in advance

Olaf

[AlvinL]

Any leaks?

The high side switch is just behind the right headlight and simply put, one 16 oz. (readily available in the States) is enough to stop the compressor from cycling. I can't quite remember, but I think it should be around 30 psi?

Bay13 - 850 S/V/C 70 Air Conditioning System

According to this, if you do a full evacuate, 1.6 lbs. (726 g) of R-134a should be put in.

[mbsl98]

I think the specific anwser to your high side valve location question is that there is no high side valve in the 850 system, just a single low pressure port behind the right headlight. When my 850 starts to cycle on and off every few seconds, it generally takes a full 12 Oz can to bring it up to pretty full presure (max 45 psi when running). It if has been allowed to leak further, then it can take two full 12 Oz cans to be maxed out (from an essentially empty system). This is not the techincally correct fill amount, but does work well. The system shuts down when the operating pressure drops to about 20 psi. Once it stops, the pressure builds back up if there is still some freon, and when it gets high enough, the pressure switch lets compressor start up again, and it runs untill pressure drops to cut-out. As teh remaining amount of freon drops further, the pressure while the compressopr is off is never enough to let the compressor cut back in. If you test the pressure of a fully charged system that is not turned on, the presure can be up around 100.

As far as leaks, the evaporator under the dash is the most talked about, and biggest pain, but there are a number of other common leak points to check before resorting to the evaporator fix. One big one is the drier cannister in front lower right of engine bay, accessed from under the car with the splash shield removed. I just had one of those replaced on our '98, although our '95 is still OK (very rusty, but not yet leaking). Any pinhole in the condenser that is out in front of the radiator can sleo leak, and this is just from road debris. Any number of the connectors can leak as well, and the fill valve itself is notorious for failing (some techs replace the schrader valve at every AV servicing as a result)

[850_olaf_nz]

ahhh! That'll be why the specialist couldn't find the high-side port last week. Many thanks for the detailed explanation.

This gives me something to work forward on.

regards

'olaf'