I've recently fixed some vacuum issues on my 1987 S4 Auto with my AC. Been doing ok since then, but I ran into a few issues over the weekend I thought I'd breeze by for some advice. Since I did the vacuum fixes, I've pretty consistently been getting temps about 30 degrees cooler than the outside temp. Usually in the 45-60 range when it is 75-90 outside. But on Saturday on a pretty long drive, the AC just wasn't doing it anymore. It was hot out and sunny. And we were sort of stuck in traffic. I was getting about 70-75 degrees out of the vent. I want to say it wasn't really more than the low to mid-90's outside at the time.

At first I was thinking there was a leak in the AC system and the freon must just be getting low. And maybe that is the case. Either way, I'm still going to run it in and have the guy who last filled it up do a check up on the level. But the next day it was more overcast and not as hot and the AC was running fine and ice cold again. I had to pretty much turn it way down even. So now I'm thinking maybe it wasn't the freon level.

Anyone have any suggestions? I was looking around and I was thinking maybe it is an issue with the interior temperature sensor to the right of the center comb vent. But I've not heard that much about it.

 

With the temp slider fully to the left the temperature loop is disabled and you are in maximum cooling mode. At this time you are getting all the colling you can get regardless of the temp sensors. If it wan't cutting it here its an issues with to AC loop (most commonly insufficient charge, or compressor issues).. or its the heater getting hot when it shouldn't due to a water valve issue.

There may also be distribution flap issues though this doesn't cause warming really - just lack of full face flow.

If you get poor temperature control when the temp slider is in the middle 3/4 of its range then it may be a sensor loop issue - but max heating & max cooling must work correctly to really deduce this...

Alan

 

Ah, that is good info to know. Yeah, the slider was all the way to the left. I've already replaced the heater control valve, so I don't think that is an issue. The compressor was swapped out by the PO, so I guess all signs are pointing to insufficient charge. I'd been thinking of going through the whole system and replacing all the O rings to make sure everything done. Does anyone have a good write up of that process? I believe there are 14 total O rings that need to be replaced.

I also had topped off the regular coolant the other day when it was a bit low. I surprised that it actually was quite a bit low. And I just used anti-freeze, no distilled water. The engine seemed to be running a bit hot after that, but I wouldn't think that would cause this issue. I'll probably do a complete coolant flush in another month or so anyway to make sure everything is set there.

 

Oh, and yes, I'll do my best to identify a leak, assuming the charge is lower than it should be. I assume it will be one of the O rings, but will check the whole system as best I can to make sure it is a line or something else.

 

You're not alone here. I know my R12 charge is good and if the ambient is above 90 F and sunny, it just blows cool. Below 90 F, and it's so cold I have to turn it down. Now above 90 F my car will run just a hair below the last white line. Below 90 F my car runs between the middle and last white line. Overcast skies and sunny skies make a difference too. I also have a clear UV tint on the windshield, which seems to have helped somewhat. I have just assumed that with the higher engine temp that is the way it is. Let us know what you find out.

 

Well, glad it wasn't just me. This was also the first long trip I've taken with the AC working, so I actually ran the AC pretty much the whole time. And it wasn't just a little hot, it was pretty hot. I'm used to seeing it between the two top white lines, maybe a bit closer to the top. It was getting above the top white line. Maybe even halfway between the top white and the bottom of the orange line thingie (not actually on the orange line at the very top). So I was quite concerned. NEver seen that before.

But as long as we are talking about oddities, how about this one: I noticed the speedo goes down when I turn on the AC switch. Yep. Seriously. I have a Escort Passport 9500 and finally got it set up with the smartcord hardwired in,s o this is really the first trip I've taken with a radar detector in the 928 too. It's integrated in with my iPhone and the app tells you how fast you are going. I've used it plenty of times with our other two cars and the speed the app said was always pretty close to the actual speed. In the 928, it was saying I was going about 5mph faster than my speedo said. Then I noticed that if I turned off the AC, the speedo needle would jump just a little bit and it wouldn't be exactly right, but more like 2-3mph off.

 

Well check the cooling fans too - if you lose a fan one on an S4+ the other fan will run at full speed all the time - you may still see some ovetrheating and the AC performance will go to hell because half the condenser isn't seing much airflow - except at high speed...

Both fans should always be doing the same thing off, 1/2 speed or full speed if they are doing different you have a fan/controller problem.

Alan

 

I assume this is just the fans by the radiator, right? And I should test it by just running the car and watching them?

 

I thought I'd give an update. I brought in the 928 to my mechanic to have him check the freon level. To do this he had to pull out the freon and then refill. He pulled out 2.20 lbs. of freon, which is actually over what I figured should be in there. They must have went off the spec for filling the old R12. Per someone's thread, I believe it should have been 80% of 1040 grams (the amount for my 1987, front only AC 928), which figured to roughly 1.85 lbs. That is what we refilled it to this time.

The last time we filled it was in late June, so that seems to indicate to me I should be good on leaks. Or at least if there is one, it's so small that I don't have to worry about it. Good news!

But when I drove it afterwards, it was blowing out just below 60 degrees. Outside temp was in the 80-90 degree range. It showed 90-100 when I first went going but then when I left the thermometer in the shade later it was more like 80. Either way, not ideal but probably nothing too bad that I had to worry about it.

And the dual fans in the front seemed to be working fine from the few minutes I watched it.

Not sure what the next step is or if that is just as good as it is going to get.