Sorry...Another a/c question about ECV
 

Have an '89 Carrera that keeps losing R134. Just had the system evacuated and recharged. Static low pressure was down to 40# after a year. No leaks detected by two different shops using dye and sniffers.

The last shop said my dynamic hi pressure was about 400#, the low side was about 40#. They think the ECV is bad and hi side pressure should be closer to 300# or so. They had to remove some R134 to bring pressures down to normal range. Vent temp today was about 60 deg. at 90 deg. OAT.

Don't know if the second shop is on the right track or not. What do you think? Bad ECV and probably leakage from some non-barrier hoses?

I know it's a slippery slope. Don't want to chase this into the ground with a shop that may not be on the right track.

ECV? is this system different than most cars? i assume they are talking about the expansion valve? the expanion valves i have seen go bad usually have a much lower hi side and a higher low side.

did they check the vents for an evap leak? that is a very common part to leak. how long did the last charge last?

condensor air flow is a big problem with these cars when servicing the AC. i usually put a box fan on the rear decklid to blow air across the rear condensor, and a fan at the front of the car.
if the airflow is not good, the pressures will be hi, especially the hi side.

when they removed some 134, did the temps get any better? and again, poor condensor airflow will raise the vent temps. what are the temps while driving with the fan on hi and recirculate?

do you a front and rear condensor?

More Info
 

Thanks for the response. Here are answers to some of your questions.

1. I don't know if they checked the vents for leaks. They were OK on the last refill.
2. A charge will last maybe 3 months before the air loses cold. Starts out about 44 deg. and goes to over 60 deg. in that time period.
3. They didn't use a box fan over the rear condenser. The temp right after refill wouldn't get lower than about 58 deg even when driving on highway with it on full
4. Yes, it has a fr/rr condenser
5. I don't know if temps got cooler after removing R134. They did it to lower hi side pressure.

The first shop got the temps to 44 but I don't know if the pressures were high. They didn't make note of it like the second shop.

I'm just not sure the shop is aware of the peculiarities of the older cars. Don't want to chase one part after another. Every part change means another evac/recharge.

That would explain your high pressure. There needs to be good airflow across the rear condensor either by closing the rear decklid or by using an external fan like a box fan setup T77911S described.

Thanks
 

Thanks guys. That's why it's important to know these cars and how they behave. I'll have the shop put back the proper amount of R134 and hopefully bring the vent temps down to around 44 deg. again.

I'm still faced with the problem of gradually losing refrigerant over a three or four month period. Nobody has identified a leak with a sniffer or dye so far. Maybe it's just the non-barrier hoses leaking.

This morning the OAT was around 72 deg. here and my vent temps got down to 44 deg. I think I'll hold off on replacing the EV until someone can more definitively identify a leak. At around $160 for an evac/recharge things get expensive quickly.

If 'they' have put dye in the system and it shows no leaks(assuming they took the time to check all the connections), you may have a non barrier hose leak. As fast as your's is leaking out, I'd be checking for a leak somewhere that 'they' haven't found. The leak needs to be adressed before condemning parts. Also, has a high/low pressure cutout swith been installed? This is an EPA requirement when retrofitting A/C, but almost no one does it.. It will save your compressor if your system pressure gets too high or too low and it's an easy install. If 'they' don't know about it, pm me and I can send you a part # or send you one at my cost plus shipping..

air moving over the condensor is basic AC knowledge.

they should have "sniffed" the vents to determine if the evap is leaking, again, a major source of failure for leaks. if that needs to be replaced, replace the expansin valve too.

i may be wrong, but 58 may be about right on a really hot day. thats about what my volvo would blow, and they are known for poor AC systems.

if you have a front condensor fan, make sure it works.

3 months is not very long, even for hose leakage. i would image at one time it was holding a charge longer than that.

you can get one of those recharge kits from advance that has an idiot gage on it and dump a can in every 3-4 months or it may be time to replace the evap.

It's entirely possible that the high pressure "broached" the o-rings temporarily. I suggest, again, that you have the shop add a hi/lo pressure switch to open the compressor clutch circuit if the refrigerant pressure gets too high or to low, lack of refrigernat.

PM to Neel
 

Neel- I sent you a PM but I'm having "cookie" problems with this site. please let me know if you received it.

To the rest of you guys, thanks for the info. I need to bring the car back next week to have them check it again for dye leaks. I'll have them re-sniff the vents but I think they did it the first time since they were sniffing around the EV in the smugglers box.

If they aren't familiar with air-cooled 911s they could be missing a lot of potential leak areas. Front condensor, receiver/dryer in wheel well, not to mention that there is something like 25 feet of AC hose in the system and much of that length runs under the car where it is somewhat exposed to impact from road debris. Also check the compressor shaft seal. If there's a leak there you will see a 'stripe' of oil underneath the decklid just above the compressor.

The shop may not be intricately familiar with the air cooled cars but they did check hoses, both condensers, the dryer, the compressor and the evaporator area. There are no moist areas anyone has found, no dye leaks found, and no positive sniffer results.

They probably did miss something but I don't know where. I think it's time to bring it to a true air cooled specialist. Hate to drive 90 miles into the Bay Area but that's probably what it's going to take to find this.

"..stripe of oil.."

Stripe of debris from drive belt close to the same area on the lid is normal.

if they did not find anything and it is leaking out in 3 months, the evap is leaking.