RichS 1986928

Ok, there is a LOT of info on here about AC problems and I've
read a great deal of it.. but I want to run this by anyone willing
to help in an attempt to stop fixing things that aren't actually broken!

Here's the symptoms

3 year old compressor, low miles, R134A conversion.

AC is only cold when it's already cold outside But it is working.

Climate control only goes cold when all the way to the left, this
used to be a problem cause the car would get too cold and I had
to turn it on and off. Now the car doesn't get cold at all.

I've tested the vacuum lines, they all hold about 15lbs.
The connection going to the blue line is giving the blue line vacuum.

I've watched the (new) heater valve under the airbox close as soon as the
car starts, this happens if the AC is ON or OFF.

Today driving it at about 50mph I noticed that the air coming out of the
center vent is much stronger when going faster. But the blower is working.

The final clue is that there is a 'hissing' sound coming from the center console
when I turn on the AC.

Any help would be appreciated. I would LOVE to fix this problem..
black car = hot car...
Thanks.

SteveG

Well, . . . . operating from your premise that you have adequate R34 and the compressor is engaged, it would be good to know what pressures the A/C system is showing when running.

you seem to know you have a vacuum leak somewhere. That needs to be corrected for the general good. I believe you do need to ascertain you have vacuum to the control head, coming thru firewall and accessed by removing the carpet panel next to driver's knee (hose not the head).
the heater valve (diaphram inside) could still be leaking even tho you see it turn to close.

RichS 1986928

Compressor definitely engaging.
R34 'should' be decent. I've seen zero leaks and again it does blow
cold air, but only when it's a bit cooler outside.. But it blows
colder than the outside air.

I have 15lbs pressure coming through the firewall on the black source line.
Heater actuator under the air box is brand new. That's the only actuator that
I've replaced.

If I pump up a colored line with the mity vac they continue to increase and if I leave it at 15psi
they slowly decrease. Is this normal? Or should they hold the vacuum consistently?

Mrmerlin

do a search for fix your HVAC system this will lead you to a thread thats addresses the outside temp sensor from your description one of the sensors isnt working or connected and usually the outer sensor in the front of the left front wheel well is usually the culprit as the system will only give full cold if the sensor strem isnt functioning. Also recheck the console vacuum pots by removing the driver side console cover. Look for a Pirtles writup on this

RichS 1986928

Thanks, I've read both of these, I think you are definitely right about the 'full cold' problem.
However I haven't gotten to that problem yet because it isn't cold at all right now.

I tried diagnosing which AC actuator was bad by using a mityvac on the colored lines, following
the various write-ups. They seem to hold vacuum. The hissing must be a vacuum leak
though? I guess I'll check them again by plugging the hoses with the car running and see if
the hissing stops.

Dark Blue

I had similar problems in my '89 S4 and after much frustration it turned out to be the AC head unit. It was expensive to replace, but solved my strange AC symptoms.

Steve

RichS 1986928

Thanks Steve, I've got a friend out here with the same car so maybe I can persuade him to swap
for a bit to try that... Waddya say Matt?

I've gotta figure out the hissing and test the outside temp switch first though.

leperboy

You're assuming mine is good... Since I have never had my A/C working, I have no idea, but you're welcome to try a swap. I still have never even diagnosed my A/C.

I need to borrow your ABS relay sometime when I'm getting an ABS warning on start-up.

Matt

RichS 1986928

Thanks Matt, maybe I'll see you tonight and I can comisterate..

Ok, I rechecked every vacuum line and they all hold 20psi.

I pulled the passenger tray and can feel the re-circ vent opening and closing just
like it should.

I can see the center vent and it's opening and closing.

I still have that hissing noise.. what's that all about? I actually disconnected the black supply line
to all the vacuum and it was still there... a little quieter though. Maybe it's just like a whistle passing
by something?

Now I'm not getting cold air at all. I'm going to try one of the Autozone recharge kits.
Can anybody tell me where the low side port is to connect this thing too. I'm already
at R134A so hopefully it should work....

dr bob

Do you hear the hissing before you start the compressor?

If you can use your miti-vac to pull each of the actuators with minimal to no leakage, you are doing pretty well. Go to the 4-way fitting by the brake booster, and pull vacuum with your miti-vac there, on the line running to the HVAC system. It -should- be OK, since you report seeing the heater valve pilling closed on engine start.

Virtually all 'not cold enough' complaints from 928 owners seem to come from not enough refrigerant left in the system. Most systems leak, and we don't realize that until it gets really low and it just doesn't get cold anymore. There's a case for using a set of gauges to see what's in there, and that would be my first step since I have those gauges. Meanwhile, you can also look in the little sight glass on the top of the receiver-drier, and see what's flowing there. Start the engine, and go look at that sight glass with a good flashlight. Then have someone push the AC button and get the compressor turning. Almost immediately, you should see foam and some liquid flowing, and the foamy flow should clear to an almost pure liquid stream. A few bubbles are normal, maybe a very light flow of bubbles in a stream of liquid. You can easily see this with the flashlight, especially if you wipe the little sight glass off first. A system that's grossly undercharged may still have enough pressure to set the pressure safety switch, but not enough refrigerant to compress, condense, and expand. Good news is that R-134a is cheap. Bad news is that you really do want to fix the leaks.

RichS 1986928

Thanks Dr. Bob, What I found.
1. No the hissing only comes after pressing the AC button.

2. I connected the mity vac to the Black AC supply line under the hood. It does
NOT hold pressure. I rechecked all of the colored lines going to the
actuators. They all hold pressure. So it appears this leak is in my
vacuum solenoid module itself. Anybody had any luck repairing that?
I looked on PET and it doesn't look like it's sold as a complete assembly.
I guess I'm going to have to pull it out of there and look for a leak.

3. I checked the sight glass, it starts out foamy and then clears up. There
are definitely still bubbles in there, I don't really know if there are too
many. I am going to try and put more R134A from Autozone in there and
see what happens.

Is there any way a do it yourselfer can find AC leaks or do I need to take
this to a shop?

thanks,
Rich

dr bob

If it starts out foamy, and then clears to just --some-- bubbles, there's enough refrigerant in there. Don't add any more. In the meanwhile, disconnect the supply line at the manifold in the console and plug it. Then miti-vac from the booster ened again and see if the line itself is intact. If it holds OK, then attach to the manifold itself where the line from the booster connection used to attach. If that doesn't hold, go do each of the individual actuators by disconnecting the line at the manifold and pulling on each with the miti-vac.

If you were hearing the hiss only when the AC button is pressed, it's quite likely that the comb flap actuator is the one that's leaking. That's the one that pulls the deflector flap in the center vent. Pull the grills out and you can look in there and see the comb flap. Hinges at the bottom, vacuum pulls it out of the way when you have the AC on so more air comes out the center vent. A fringe benefit of the comb flap actuator leak is that the heater valve will be starved for vacuum when you push the button, but will work fine when the AC is off. So your diagnosis of valve OK when starting the engine is still valid. Look at that valve as you have someone cycle the AC button, and you might see it slowly open some as your vacuum bleeds out.


So--- The dr's prognosis based on your description of symptoms is comb flap actuator leaking. There are a couple good repair descriptions around. I read and followed the one at John Pirtle's renn website, and it was fine. The diaphragm that leaks is replaceable without replacing the whole housing or the actuator arm, but you will need to disconnect the arm from the lever on the comb flap to do it. I think that Roger offers just the diaphragm as a replacement part, or buy the whole actuator from one of the Usual Suspects and scavenge the diaphragm.

RichS 1986928

Ok here's where I'm at after messing with it all morning.

as a recap, the compressor is practically new and I replaced the dryer when that was done.
No rear AC.

Vacuum, Everything checks. It appears there was a small leak where the coupler from the
black line goes into the solenoid manifold, I fixed that. All actuators are good. The comb flap
goes up immediately when I start the car... and doesn't come back down until I turn the car
off.. even if i try every position on the Climate Control Module.

Temp sensor under the headlight is good, I soldered the connections together to eliminate any problems
with that connector.

The hissing is still there.

It's there even when I dissconnet the black vacuum supply line and plug it with my finger! And
no it's not the supply line itself, I checked that. What the heck else can this hissing be?
It happens when I turn on the AC button. It persists after I shut the car off and I can hear it slowly
dissipate.. Is this leak in the AC system itself and not a vacuum leak at all? Where should I look for
this?

Also I hooked up a can of 134A, the gauge said 'low' So I put some in to the 'full' mark, it seems to
be holding, but the AC is only cool, not cold.

This is Driving me NUTS!

ew928

Random thoughts.

Is the recirculation flap (one on passenger side up under the glove box) closing all the way. Recirc closed with A/C on so system keeps chilling the same air instead of trying to cool ambient outside air.

Is the seal between engine compartment and HVAC air intake good?
It's the seal in front of the plastic self breaking cover that resides just in front of the windshield by the hood hinges. The seal keeps the hot hot hot engine compartment air from being ingested by the HVAC system. (Tip from Wally P.)

Is the hissing hissing? Can it be whirring?
Only asking cause the center dash interior air input fan is in the dash and it might be making noise. (Long shot). Not sure how to pull power from the fan to eliminate it as a noise maker.

RichS 1986928

any help is apprecitated.

Recirc flap is definitely working.
Hissing is definitely hissing, not mechanical.

Is the seal between engine compartment and HVAC air intake good?

where is this?? I attached a pic...