a/c question
 

the a/c on my son's 85 has never worked - since he's spending a bit of time in it this summer he asked if we could look at it - it has a r134 fitting down on the compressor so we tried just re-charging it and the compressor spun up and it blew cold air..for 3 days - obviously a leak..right? - so I put a shot of UV dye and put some more refrigerant in hoping we could find the leak - again it ran for 3 days - I got out the ultraviolet light and started hunting along all the lines - cannot see any of the dye anywhere - I can see the dye in the sight glass on the dryer so I know it's in the system - the only place left I can think of are the connections under the dash - are these common spots for a leak? - can these connections be accessed if the glove box is removed? - thanks

On the early cars the blower evaporator is behind the passenger kick panel. You can see some of the pipes and wires if you remove the kick panel.

If you have to remove the unit here is a condensed DIY:
Evaporator unit removal on early 944 - Rennlist Discussion Forums

You tried the UV dye. If you cannot see the leak you may need an electronic sniffer.

If you pull the evaporator, replace ALL seals on every connection.

You may also try to just do a total vacuum. Get a vacuum pump and see if it holds vacuum.

and.......................

GL
J_AZ

thanks john - will try pulling glove box and kick panel - after all the dye and refrigerant would almost expect to see the dye dripping out on the floor

Did you check the compressor itself for leaks? The compressor body is segmented and there are three (if it is a Denso 10p15 compressor like on the "late" cars) body seals: at the nose cap, middle, and tail cap. There is also a carbon seal on the shaft that you may not be able to see dye leaking from because it is behind the pulley/clutch (where the shaft actually goes into the compressor). Mine was leaking there quite badly but I couldn't see it until I took the pulley off. If it is leaking there, it is actually pretty easy to replace the compressor seals.

Edit to add: It can also leak around the longitudinal bolts on the front of the compressor that hold it together and the ones on top (in the "up" direction when it is mounted on the car) can also be hard to see (I think there are 5). There is also probably a Schrader valve on the compressor near where the hoses connect.

My leak was in the evaporator (inside the blower case).
Open case to inspect.

If you get this far I suggest you inspect or replace the expansion valve in the
case.

GL
J_AZ

look for dye in the condensate drain.

High pressure switch tends to leak...a lot....check the dye find the leak...don't assume it is anything...

Pulling a vacuum on a system that is obviously leaking isn't good, because you will be pulling air into the system (and with that, moisture). I wouldn't recommend that.

The absolute best way to locate the leak is to get a pair of gauges and pump the system up with dry nitrogen if you can get access to it. I'd pump it to around 85psig, and if the leak doesn't show it's face at that point, a thick solution of soap on all of the joints and fittings and look for bubbles. Don't be temped to use compressed air... Again, moisture mixing with the oil is really bad.

I'm going to guess that you've never seen an a/c system that does not leak when pressurized, but does under vacuum. I agree with your ideology that introducing moisture into the system is not good, but sometimes it is necessary to find leaks. A whistling noise under vacuum can point you towards the leak. The reason you pull a vacuum is to boil off any moisture that has become introduced into the system.

While well aware of the chemical reaction when R-134a, oil and oxygen intermingle, I've never seen ill effects of using compressed air in lieu nitrogen to find leak in a system, and I have used both. Furthermore, I would increase PSI to at least 110, as this is where most systems lie in equilibrium. YYMV, but if your ambient temp is 90+ the pressure should be 110+/- 10 with the system equalized.

It isn't rocket science. He probably has a shaft seal leak that can not be seen or heard. If you've had enough experience with compressors and shaft seals, you will soon find some won't leak when the shaft is in a certain position, rotate it a tad and it will show its ugly face.

[QUOTE=mattdavis11;8160275]I'm going to guess that you've never seen an a/c system that does not leak when pressurized, but does under vacuum. I agree with your ideology that introducing moisture into the system is not good, but sometimes it is necessary to find leaks. A whistling noise under vacuum can point you towards the leak. The reason you pull a vacuum is to boil off any moisture that has become introduced into the system.

While well aware of the chemical reaction when R-134a, oil and oxygen intermingle, I've never seen ill effects of using compressed air in lieu nitrogen to find leak in a system, and I have used both. Furthermore, I would increase PSI to at least 110, as this is where most systems lie in equilibrium. YYMV, but if your ambient temp is 90+ the pressure should be 110+/- 10 with the system equalized./QUOTE]

You'd guess wrong.

The oil is hydroscopic, and moisture is not condensable, so any moisture introduced by pulling air into the system that migrates itself in the oil creates acid and decreases the life and capacity of the system.

I mean, you're right, it's not rocket science. It's chemistry and thermodynamics. I'm trying to give advice to help someone who doesn't have any experience, not telling them how many rules they can bend or ignore without messing anything up, but hey, I guess that's what car forums are for! If he wanted it done right, he would have taken it to a shop were the people working there are held to some sort of standard work practice.

My apologies.

You do know what the boiling point of moisture is in a vacuum state, correct?
You know not to slug the compressor with oil and charge as a liquid on certain applications, right?
In a perfect world we do things differently, and it works just fine.SmileWavy

The last place I'd take my car to is a shop.

In my experience the best way to find a leak is probably to get a halogen leak detector. They aren't particularly expensive and if you plan to fix it yourself anyway, then surely less expensive than taking your car to a shop. I have one of these but even a cheap one would probably work just fine. One can beat his or her head against a wall trying to figure out where a leak is or just use a detector and find it directly.

P.S. A set of AC gages won't help locate a leak - or, unfortunately, in most cases even indicate whether there is a leak or not. If there is enough charge in the system for at least some of it to be liquid when the AC is off, then all the gage will do is tell you what the ambient temperature is.... and when running, the pressures depend on a whole bunch of things and again won't generally tell you how much charge there is. If the amount of refrigerant in the system is insufficient for there to be any in liquid phase then you probably already know that there is a leak.

At least we agree on something! ahaha

I hope that was said in jest. The only way I knew there was not a leak on a bus a/c system yesterday, was because I had gauges. I knew where all the parts reside, but most could not be seen. I did know that there was no leak because the system held a vacuum overnight. If there was leak, you are correct, gauges would not have helped to locate it. Thank goodness there wasn't one, there's 100 feet of hose on that Monaco.

ok - I don't have access to this car all the time so I've been slow to answer - looked at it the other day - pumped even more dye in - same result - took off the passenger panel and I can see two connections to the evaporator - both are clean and dye free - looked at the drain under car - no sign there either - so what I think i'm left with is a leak inside the evaporator case or a leak behind compressor pulley - a question - if the leak is behind comp. pulley would the refrigerant evaporate so fast as to leave all the dye as a "lump" behind the pulley so I can't see it - same with inside the evap. case - my son (physics major) says yes it would evaporate almost instantly so the dye could never actually flow out where we can see it - going to try pressurizing it with air and spray with soapy water next time I see car - in a few more weeks it will be moot as he heads back to school and the future of the car is up in the air - thanks

My bet is that you probably have a compressor shaft seal leak I just got a rebuilt compessor for $200. no core required from www jensen motor parts filled with 2#of r 12 lasted 2 weeks the short line from compessor to condensor started to leak $20 bucks from gravesjeg Aquick vacume 2# of r 12 and super cooling I've seen r 12 on criags list for cheap but with a set of gauges and a30 # of 134a you don't need to change your access ports just change the oil another great tool is a halide torch the flame changes color when it sucks in leaking refegerant it's cheap to buy

would have can of 134 with leak stopper help in this situation?

the can of refrigerant I was adding has leak stop, dye, oil, and I think seal conditioner - didn't help

A can of refrigerant with stop leak is the worst thing you could introduce into any a/c system. Take a look at the compressor, is it coated with oily grime? If so, you found your leak. Shaft seal.

ok - the compressor top was totally gunked up around the hose attachments - so I got a o-ring kit for this compressor - replaced the O-rings on the top and also the ones where the hoses attach - I don't know how much of a vacuum you need to test this but I got down to 17 inches of mercury and let it sit overnight - it held that much vacuum - put a can of r134 in and ran it - it was pretty cool so I put another half can in and the vent temps would range between 32 and 40 degrees - so it's fixed right? - not so fast..some green drips on the floor (remember the dye I couldn't find) - well its easy to see now coming out of a bolt (plug) next to the sight glass on the dryer - I looked at those connections 2 week ago and they were dry - what is this plug for and why does it have a hole drilled in it - that is actually where the leak is...that hole - anybody know what it does? - looks like all that refrigerant will be gone by morning - spent the better part of the day doing all this so i'm pretty annoyed right now - thanks

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