96 850 Turbo: is there are relationship between a bad cooling thermostat and AC functionality?

insession · Post by **insession** » 12 Feb 2022, 23:03

My 96 850 Turbo has had a cracked radiator for months, which I fixed with JB Weld, but after months now the fix is coming loose and this week I am having the radiator replaced.
Maybe coincidentally, a week ago the temp gauge started to react erratically, ie it goes up to say 80% too fast, and then drops back down to say 50% too fast as well. So while there's some apparent overheating, I measured the temp on the upper and lower radiator hoses, and while the bottom was ok at 30 degrees, the upper one was too hot at 90 degrees, which indicates to me that the (original) thermostat just went bad, and I am getting that replaced with the radiator.

Now then, it's winter in San Diego, and until today I've not used the AC - but it's 85 today and to my surprise it didn't kick in, yet a bit later did, and then again stayed off. Even with AC on full the compressor seems to engage only intermittently. I've done the famous shimmy ghetto repair on the compressor years ago - which fixed the widening gap - and have refilled the system with a couple of cans of refrigerant a year ago when the AC was no longer cold - which fixed it. Today pressure (with the car running and AC on full) at the lower/fill valve fluctuated, but leveled out around 40psi, in the green area of the gauge.

All this intro to provide context for my question: is there any relationship between a faulty main cooling thermostat and the AC system? I don't think so but wanted to ask all of you experts. And if there's no relationship -- any clues what may be ailing the AC system now? I've replaced a broken upper switch (close to the firewall) some years ago too, it seems to work.

Thanks fellows,

Peter

Post by **misha** » 13 Feb 2022, 07:13

Might be if car is equipped with ECC...since ECC module use the data from ECT.

insession · Post by **insession** » 13 Feb 2022, 09:36

Yes, I do have an ECC. Sounds like maybe the ECC prevents the AC from kicking in when it gets the signal that the engine coolant is too hot?

insession · Post by **insession** » 09 Mar 2022, 19:27

As misha suggsted, the ECC turned the AC compressor off when the car was overheating.

Since then, I've had the leaking radiator, malfunctioning main thermostat and the temp sensor right below that replaced. The car now runs cool as a cucumber

However, now my AC doesn't come on at all. Clutch is not engaging. Given that it worked well (on and off with cool/hot temps) a week ago, what could it now be? I bridged the high pressure sensor, no dice. Clutch is free, using stick to engage it no dice. Fuse #31 (AC) is ok.

I've read up on this online a bit, and have come up with the following possible culprits:

AC relay (behind glove box?)
Baro-sensor (should be by ECU box?) and acceleration sensor (on subframe bottom front)? Confess I've never heard of either

Cooling fan relay (under fan shroud)

Thanks guys and gals,

Peter

Post by **misha** » 10 Mar 2022, 02:41

Compressor will not engage below 2 degrees Celsius...when orange lamp with snow flake is on.

insession · Post by **insession** » 10 Mar 2022, 09:32

I live in San Diego, it's never cold enough for that here

Post by **misha** » 10 Mar 2022, 12:22

Then....it's just low on freon.

insession · Post by **insession** » 10 Mar 2022, 15:40

Thanks misha - my reason for doubting that is that it worked just fine after I filled it back up last year, and just fine (albeit on and off due to overheating) until a week ago...

insession · Post by **insession** » 10 Mar 2022, 15:41

Oh, and I forgot - a week ago when I was trying to find out why it was erratic, I checked the pressure on the fill valve, and it seemed ok, settling around 35 or so when under load...

Post by **misha** » 10 Mar 2022, 16:24

Ac is more complicated than that.
There is professional equipment to check pressures in the ac system and pressures are different in different ambient temperatures.

When it comes to AC i always service it in professional AC shop...every 2-3 years.