BobbyT

My AC isn't holding refrigerant. Cooling was poor, pressures were low, so I added one can of R134 a week ago, which brought pressures within range (17/275, vent temp 51 @ 93F @ 2000 RPM).

Today cooling is poor again, so I checked pressures and found 2/150 @ 73F. I added yet another can of R134 with UV dye (I already have some dye in the system), which resulted in 16/270 @ 82F, vent 51F.

So, the system works well enough, it just won't hold refrigerant. Even with the dye in the system and using a UV light, I can't find any evidence of leaks. The drain under the car is dripping water only, no oil or dye.

My wrench says "all the 993s puke the evaporator sooner or later", and he seems eager to replace it. If the evaporator was leaking, wouldn't there be some dye or oil showing up on the garage floor?

I've been told there is a little catch pan that is barely visible looking down past the expansion valve with a mirror, but I don't see any wetness or dye down there, either.

There is no sign of leakage at the compressor or anywhere in the engine bay.

I think my next step will be to take out the LF fender liner and check the receiver/dryer and condenser for leaks.

Are there any other "usual suspects", or something I'm overlooking?

I'm reluctant to tear into the evaporator until I see the source of the leak...

TMc993

In my experience, if the system holds pressure for a few days, the leak is usually so small that the dye doesn't pool up. Instead, you get a telltale trace of dye at the location of the leak(s) and it isn't always readily apparent. While your mechanic is correct that 993 evaporators often leak, I would want to know that was definitely the problem, and the only problem, before I authorized what is surely to be an expensive repair.

BobbyT

Hi Terry,

That's helpful. And yes, I want to see some evidence of the leaks before doing any repairs. I replaced the AC compressor on one of my cars long ago, only to find while I was doing the work that the culprit was a 50 cent O-ring.

P-daddy

How would you know if the evaporator is or isnt the problem until you authorize the work to be done. By then you're several hours $$ into the job.

ble2011

I was told my compresser is leaking when I took it in to be recharged. It's going on 2 summers now and still working great. Not sure if dye would work for mine as well.

JM993

Did you check the valves on the compressor? I had a similar experience troubleshooting a 993 and it was the last place I looked. When I took the cap off, the inside was green! If it's not the issue, you will need to follow the lines from the rear to the front of the car. This means removing the wheel arch liners and rocker panel. so you can inspect the lines and the condensor. I wouldn't dig into the evaporator unless I knew was bad.

Hope this helps

NC TRACKRAT

+1 to what JM993 said. Our '95 has had a history of losing its charge over time. We just evacuated and re-charged, then used a highly sensitive electronic "sniffer". Lo and behold, the only leak found was at one of the compressor valves...an easy fix. (These are supposedly proprietary Porsche parts-No commercial equivalents). BTW, as has been stated before, our systems require an exact amount of refrigerant to be at optimum. Too little or too much has a detrimental effect.

TMc993

P-daddy,

I have had a similar situation in my 993. When I described it to my shop, they proposed that they evacuate the system, recharge it with a dyed refrigerant, then drive it with the AC on for a while to see if there were leaks. They found a leak in the evaporator. No other leaks in the system. I decided to "ride" it for a while, but I at least I knew where the problem was.

The key was careful testing and diagnosis of the problem before requesting authorization on the repair work. My shop always does a precise diagnosis before requesting authorization on repairs (Which is what I did not see in the OP's original post).

Hope this helps...

BobbyT

NC TRACKRAT,

Was the compressor valve you mention one of the service port connections, i.e. for the low and high pressure lines to connect to the test gauges?

luckyJ

sorry, what does it mean if the low side pressure valve cover is green?

BobbyT

When dye in introduced into the system, this is done via the low-pressure valve, so there will be some dye visible inside the cap and in the valve inlet as well. The dye I use is yellow, but it might appear light green to some. This is normal, it doesn't indicate a leak.

JM993

Yup, that's it. Hopefully that's your problem. Easy fix.

luckyJ

whew...ok, thanks for clearing that up....I've noticed a hissing sound coming from the right front dashboard area when using the AC....it comes and goes....every 20 sec or so when I'm stopped in traffic....is this normal?

ToreB

Evap leaks are common in the 993. It is difficult to spot any dye, it should be coming out of the drain hose underneath the car. I had my car refilled three times before I could spot any dye, most of it stays in the evap/air box housing, and the leak has to be large for it to drip out of the hose. Here's a thread with pics.

Some A/C shops can use a electronic sniffer to find leaks, tell them to sniff into the resirc flap opening under the dashboard to spot any evap failures.
Cheers,
Tore

911PERVY

Fill with 200 bar of nitrogen and sniff it