cwiert

I installed a brand new A/C compressor, new belt, charged up the system and had cold A/C for about 20 minutes. Then, while at the Burger King drive thru, I heard a suddon, "HISSSSSSSSSSSSSSSS" coming from behind my center vent. This hiss continued for a good 20 minutes and then it stopped, and then my cold A/C went bye bye. I couldn't see where the hiss exactly was coming from. I was looking from the inside of the car with the center grate removed, and from the engine bay side with that rubber bladder thingy removed. I can see a radiator like thing in there... I think that's the Evaporator.
Where do I go from here? How can I tell if I need a new Evaporator, or maybe a new expansion valve, or maybe one of the lines broke that lead to the Evaporator. Any write-ups on how to remove that stuff so i can get a better look at it?

dr bob

Electronic leak detector is best. You can try the UV dye in the oil method, but you have to have a -good- UV light source, work in the relative dark, and be able to see where the dye is leaking out.

The expansion valve feeds refrigerant into the evaporator, metering it so that the liquid flashes to vapor. When the system is undercharged, the refrigerant is no longer vapor as it gets to the valve. The sound you heard is most likely the refrigerant gas passing through the expansion valve, as the valve opens wider to get more cooling. Recommendation: Find the leak(s) and fix.

If your compressor replacement was because the old one went boom internally, the system needs to be flushed completely before the new compressor goes in. If there was/is -any- grey powder in the hoses, the system must be flushed before you install your next compressor.

If you didn't do it the first time, replace -every- o-ring in the system with the new material rings.

If you didn't do it the first time, remember to measure the oil in the system and only put in what's required.

Installing a compressor with oil in it, you'll need to rotate the compressor by hand to clear any oil accumulations from the cylinders before you turn it on with the engine spinning. The compressor may hydro-lock with the oil if you forget.

Good vacuum, big pump, lowest pressure, longest time, coldest system. They are all interdependent.

cwiert

thanks dr. bob!

Z928328

My car had the evaporator change last month after few attempts to regas & lose out like one day or within hrs & the shop find out its the front evaporator with the electronic leak detector.. The shop use an after-market evaporator(from China) - So far so good.-

http://i640.photobucket.com/albums/uu122/z928328/Dashout.jpg[/IMG]

http://i640.photobucket.com/albums/uu122/z928328/Newvsold.jpg[/IMG]

http://i640.photobucket.com/albums/uu122/z928328/Coolingcoil.jpg[/IMG]

cwiert

ok, i'm just rereading this again, and it seems like this may be good news. what you're saying is that my evaporator may be fine. What I failed to mention in my OP was that I did find a leak immediately after charging the system. There's a little glass window on top of the receiver drier. I saw liquid bubbling from around the edge of that window...so i knew there was a leak. And according to what you're saying, once the system leaked enough and became undercharged, that's when I heard the refrigerant gas passing through the expansion valve...HISS.

SO, if (a big "if") that is my only leak, then i should just need to replace the receiver drier and re vacuum, and re charge, right? maybe it's not so bad after all.

AO

I really hate to say this, but the bubbles in the receiver drier are normal.

You really need to check out Wally's HVAC write up on the 928 Specialists website (928GT.com then look for "Tips" on the left hand column).

cwiert

the bubbles weren't "in" the window, it was bubbling and leaking stuff out from around the window. that can't be normal, can it?

anyway, thanks for the reference. i'll check out that write up right now.

AO

Got it! You're right. Leaking stuff out of the window is not normal. However seeing bubbles through the glass is normal.

dr bob

The little window is a sight-glass, used in some systems to help estimate (broad-brush guesstimate....) the level of charge and/or NCG contamination in the system. The Good News is that the sight glass is in the receiver-drier, a part that should be replaced every time the system is opened for service.

Read Wally's excellent HVAC reference. Consider that the reason you (or the PO) are adding refrigerant is due to leaks. If you are the most fortunate 928 owner in the world, the leak you saw on an exposed, easy-to-replace, you needed to replace it anyway part like the drier, is the only place the system is leaking. If you are that most-fortunate owner, I bow down with hat off to you. Meanwhile, back at reality, there are a couple dozen other places for refrigerant to leak. You mentioned replacing the compressor, and I'll remind you that they -never- fail painlessly; there's virtually always debris from the parts that wore out, floating through the system, waiting to foul your new parts and trash your new compressor. CYA says have he system flushed well before resealing and recharging.

JHowell37

The leak is probably in a location that was disturbed when you changed the compressor. Are you saying you charged it and hopped right in the car and went to BK? I'm trying to figure out just how long there was refrigerant in it.

If you went from charging it to having it empty in 30-40 minutes time, then it's leaking fast enough that you should probably be able to hear it. Even more importantly, you should probably be able to feel where it's leaking out. The area around the leak should be cold.

If you put in a new compressor, you're supposed to change the receiver/drier. A new expansion valve wouldn't hurt either.

cwiert

a buddy of mine has a friend who has a shop with a new AC tester/vacuum/charger. i knew the compressor was seized so i replaced it. i didn't know i was supposed to replace the drier too. we installed the compressor and drove to the shop where we did a 15 minute vacuum and then the machine ran a "test for leaks" which the test failed. Since this was all free, my buddy said, well, lets just put some refrigerant in there and maybe we can see where the leak is. So we did, and I was getting cool air. We drove home, and i spotted the bubbles coming out of the side of the window in the drier. So my buddy said, "there's your leak." So I thought I just needed to replace that and I'd be good. I then drove to BK (15 minutes away), with the AC on, and while i was waiting at the drive-thru, i heard the loud hiss coming from the front vent. I turned the AC off, but the hiss continued. after about 20 minutes, the hiss stopped, the bubbles from the drier stopped, and if i turned on the AC, no cold air was to be found. I'd say 30-40 minutes is right. It leaked out that fast.
So all in all, Dr Bob is probably right that the leak I spotted in the drier probably isn't the only leak.

Bill51sdr

Agree with Dr. Bob, flush that system out before you go any further. You will need a new expansion valve in all probability now as well.

JHowell37

Do you have rear A/C?

Does the car use R-12 or R-134A?

If the old compressor had seized, without a doubt you need a new drier. You should also put in a new expansion valve. With the expansion valve off the car, flush out the evaporator. You might as well put in the extra effort to flush the condenser and the hoses/lines as well. When you put it all back together, use fresh o-rings. You can buy stuff to flush it at most auto parts stores. The stuff at the place near my house is water based and has a citrus scent. It doesn't leave any residue, but since it is water based it's going to leave water in the system. Once you get it back together, you'll need to leave it on the vacuum pump for much longer then 15 minutes to eliminate the moisture.

dr bob

The debris fiueld from a siezed compressor extends through the pressure hoses to the condenser, the drier, and on to the expansion valve. Those pieces all must be flushed or replaced. The evaporator is somewhat protected by the drier and the expansion valve, but at that point it's not big extra effort to flush that and the low-pressure return to the compressor. New drier and expansion valves.

"Seized" on the old compressor means that pistons ran dry until they welded themselves to their bores. In that process, fine grey aluminum dust (used to be the pistons...) is circulating through the system, gathering in low spots and wherever there's oil residue to cause it to park for a while. Your mission is to get ALL that old aluminum powder and contaminated oil flushed out.

Pull the compressor and carefully drain the oil in it onto a clean white rag, looking for any of the grey dust in the oil or in the suction lines to the compressor. That metal dust is death on the new compressor. You may be able to flush the compressor out on the bench, then put new clean oil in there and pray. Hard! Your friend's AC buddy should have flush stuff available, and guide you through all the rest of the love and care needed to have reliable cold AC.