Steve J.

My system worked well with R-12 but would not hold a charge. I decided to reseal the system and convert to R-134a. I replaced every o-ring and flushed every line and replaced the drier. I added 8 oz. of polyoester 100 - half in the compressor and the other half distributed among the evaporators, condenser, drier and lines. I pulled a deep vacuum for 2 hours and checked for leaks then charged with R-134a. At about 30oz. the rear unit cooled some but the front vent temp was 110 even though the heater valve is tied closed. Where is this hot air coming from? The sight glass never began to clear - solid fizz even at 36+ oz. Low side was 50psi and high side was 300psi. The compressor is quiet. The lines were very hot. I am baffled and not sure what to do now. Please help! <img src="graemlins/crying.gif" border="0" alt="[crying]" />

joel roeder

hi. first off the sight glass means nothing with 134. you now need to pull out the freon and recharge to 80% of r12 value. then post your presures. next, there is a motor on the left side of heater box that operates the blend door for temp control. if this motor is stuck at full heat or the arm points up you are not getting the air to flow over the evaporator and into the car.your low side presure at proper charge should be 40 or less. if you can keep the high side presure under 325 it can work better if at 80% the presures still show hi then try reducing the amount of freon. make sure your condensor fan is working and the flow is not blocked.

Greg86andahalf

Steve,

First off, don't be too concerned about the sight glass. A proper amount of R134 will show as a fizz or bubles. If a sight glass is clear with R134, the system is over-charged.

The heater valve can leak hot water even if it's tied shut due to the plastic parts in the valve warping and not making a tight seal. It's a $10 replacement part. I'd replace it just to be sure. If your car is kept in a garage, try checking the a/c when the car is first started, before the coolant comes up to temp.

Check the recirc flap under the golve box. YOu may be bringing in hot engine air. Make sure the A/C is on vent and the temp slider is full left. The flap should be up. If it is not, your have a vacuum leak. You can run a temporary vacuum line from the splitter near the black/blue check valve by adding a "T" to the splitter and running a dedicated line to the line running to the recirc flap. This line is located under the shield that hides the wiper motor and expansion valve.

You may want to read Thom's post about checking vacuum lines. Check the comb flap line. (orange line on my 86).

Are the door vents just as warm? My inop. center flap caused the center vent to be 10+degrees warmer than the door vents. I cut the line, capped the source side, and all vents are cool.

300 high side seems high.

Check the airflow over the condenser I don't see what year car you have, but if it has a clutch fan, check the fan's condition. A quick way to check airflow through the condenser is to idle the car and hold a shop rag to the condenser on the grille side. The fan should hold the rag to the condenser. If the rag falls, there is not enough airflow.

Clean the condenser fins of all debris, pick out bugs and road stones carefully with a dental pick. Flush the condenser debris out from the radiator side with a garden hose.

Make sure the electric fan is coming on. At 300PSI, it should be running.

After all of that, hook up the gauges, run the car at 1500RPM, A/C on high, windows open. Monitor vent temp and pressure while applying a cooling splash of water accross the condenser. If vent temp and pressure falls, wer'e back to airflow as a problem.

You can also try monitoring the temps and pressures, and slowly removing a bit of the R134 charge. 30OZ sounds about right, but it is possible to charge through the optimim amount of freon, which makes vent temps and pressures go up. Not good. Also hard on compressor.

One more- I understand that you flushed the lines, but did you drain the mineral oil out of the compressor?

Some places to start,

Please let us know if any of this helps,

Greg

Jay Wellwood

300 psi is too high...sounds like the system is over charged.

The flaps for the aix mix is another issue for the front - check that they are properly aligned as well as the heater vale.

hth-

Steve J.

Thanks all. I am going back to square one. There is still a refrigerant leak somewhere and I will address the flap and possible heater valve problem. I had achieved optimum refrigerant charge volume with good low and high pressure side numbers (low 35-55, high 175-250) but no cold air. While charging and monitoring vent temps, I could hear the hiss of the rear expansion valve working (with some cool air) but no sound from the front one (and hot air). They were working fine with R-12. Condenser is clean and fans are working properly. I did not change expansion valves. Compressor was drained of old oil. All o-rings were black material, hard and flat - replaced with oiled green r-134a compatible o-rings. Hoses were rebuilt.

Weissach

If the system is "over charged" it will cut off the compressor, it's that simple. It has happened to me many times, when I have gotten a little to freon happy. Good Luck <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" />

Steve J.

System would hold vacuum but not pressure. I will pressurize with nitrogen tonight and use water/soap to locate leak. If unsuccessful, I will try UV leak detection. Leak detection with propane torch and R-22 charge was recommended but I can't find R-22. Once the leaks are fixed I will try to diagnose other problems. I don't want to resort to "leak-stop" yet.

Dozman

The reason R22 was suggested to be used, is that combined with nitrogen after your through with the leak detection process, you can vent the charge to the atmosphere legally! If your not going to use a 'D-Tek' or similar device that actually detects refrigerants, it's ok to just use dry nitrogen and check with bubbles. Just don't bring the pressure too high up.
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

John D.
'85 928 Auto, Black

Greg86andahalf

Steve,

Using stop-leak will kill your system. Maybe not today, but someday, and bigtime.

Greg

Steve J.

FOUND IT! The condenser has a hole from rubbing against the power steering fluid cooling loop. Everyone go out and check your sharks! This explains the symptoms - would hold vacuum but not pressure, was intermittant, and would leak down to about 10psi and then hold. So the leak was like a one way valve and a regulator! Once the system was pressurized (35-40psi) I could hear it hissing from several feet away. Also, oily and dirty around the leak. Now what? Pull the condenser? Can it be repaired like a radiator? Greg - I agree about LeakStop - once you use it, there's no turning back. <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

Steve J.

Oops, I meant to post a photo...

Greg86andahalf

Good for you Steve!!

You did the right thing by finding the source of the problem and not just masking it with stop-leak.

As far as repairing the condenser goes, I would assume it can be brazed, but you should go to griffiths.com and ask "griff" the question. You should also run the original problem of hot air in the front vents by him too.

You can go to aircondition.com discusion board and ask "chick" about the condenser repair, he will admit knowing little about the 928 HVAC, but he will know the condenser repair procedure, if there is one.

If the condenser is repaired, it will need a major flushing. At least three times through with flush, followed by nitrogen. It's often said that the condenser can never be too clean.

It would be prudent to replace the drier again.


Also, remember to replace the oil related to the condenser (and drier, if you replace it)

From reading your posts, you seem to be quite on the ball with A/C stuff, sorry if I'm telling you things you already know. <img src="graemlins/sleep.gif" border="0" alt="[sleep]" />

Looks like your well on your way to cooler air!

Greg

Greg86andahalf

Steve,

In my efforts to learn more, I posted the condenser repair question to the guru's at aircondition.com. Here is one response I got.

"Greg,
Better off to replace the coil. That pin hole just may be an indication of some formation of acid in th oil and this one pin hole is just the begining. But if you want the use that aluminum brazeing kit by Keep it Kool. It takes very little heat and is very easy to use. Remember to take all fire safety precautions.
Vegas"

Steve,

I think you know the source of the leak (not acid) because there is a direct rubbing going on which probably caused the leak.

Here are a couple of links to the keepitcool.com site. I have read some success stories by people who have done small repairs to aluminum A/C lines, fittings, etc using these kits. The key appears to be not getting things too hot.
If I was going to do it, I would remove the condenser for ease of work plus the benefit of being able to do a better flush job by being able to turn the condenser and get the flush and debris out.

With that in mind, if a home kit may work, than a pro metal shop should also be able to do this for you if you choose.

<a href="http://www.keep-it-kool.com/braze/braze_1.html" target="_blank">Keep it cool.com / brazing</a>

<a href="http://www.keep-it-kool.com/store/store1.html" target="_blank">Keep it coll.com brazing store</a>

HTH
Greg

Steve J.

Greg-
This looks like an easy fix for a DYI aluminum brazing kit. I need something to practice on first so I don't muck it up. Maybe an aluminum can. I was concerned that the PS fluid cooling loop also had a hole but it is steel and was only shined up a bit at the spot. I will take it to the AC shop that rebuilt my hoses to get a repair quote.

Dozman

Steve,

If they can't fix the leak let me know. I have a condensor out of an '85 shark. Let it go for cheap.

John D.
'85 928 Auto, Black