into the belly of the beast.....

[560slsteve]

today i tried to chase down an AC leak on my '87 560SL. I had the freon leak detected in the engine compartment and couldnt find anything. so i dove under the dash to expose the dreaded evaporator. I also took the blower motor out and looked down the back side of the evaporator. found nothing on either side--no oily stains, etc. in fact, it looked really good and better than i expected.

so i figured it was the expansion valve---tried to disconnect it and a lot of gas under pressre was trying to get out. I got a tank and evacuauted the system, and then checked the strainer in the valve, which had some stuff in it but i dont think enuf to clog it.

so now i am at a loss---i am going to replace the evaporator valve and drier, pull a vaccuum and recharge with some dye and go from there. the system seems to cool for about 3 days when charged, and then gradually looses it cool.

would it be safe to assume that if the evaporator has a hole, the system shuld completely leak down to zero, and not have any residual pressure after a few weeks?

Is it possible that i have a bad compressor seal, and when the pressure is reduced it can hold the charge? cant see any oil residue anywhere near the compressor.

if the evaporator valve is bad, that would also restrict the flow of freon and reduce cooling?

just thrown from not being able to find any oil anywhere from a leak, when it ceases to cool in 3 days---that should be fairly noticeable i would think.

just brainstorming and looking for other opinions. it may not be a gas leak problem at all......

[wallster]

nice thread title!
The best way to find a leak in your ac unit is to perform a dye based air conditioning leakdown test that uses a colored dye to find freon leaks in your air conditioning system. Using this test, a colored dye is injected into the a/c system which will be visible under UV (ultra-violet) light at the point of a leak anywhere in the system. The test is performed under full pressure with the air conditioning system closed (sealed as if you were driving under normal conditions).
Here's what you need.

Good Luck!

wally

[560slsteve]

thanks wallster,

thats my next step hopefully this weekend after i get a few parts. just hoping to find some oil somewhere like i did on the coil last year when it began the saga of the intermittent cooling. i am sure the dye will be the best leak detector. i had really figured i would have seen some sort of oily residue also on the condensate drains if the evaporator was the culprit, but they looked good and dry, especially when it seemed to leak down in 3 days. i know there was plenty of oil coming out when i loosened the connections onthe evaporator valves initially.

i will keep you posted where or what it turns out to be. from what i got into today, anything in the engine compartment willl be much easier and i will never complain again...............

thanks

[Roncallo]

The dye method works but gets kind of restricted as to where you can use it especially without taking things apart, like the stuff under the dash. If you are loosing cool in three days you should be able to pick that up with an electronic leak detector.

A few tips on using the electronic leak detector.

1) Freon is heavier than air so probe on the lower side of hoses and components.
2) Low side has higher pressure with AC off so check this side with AC and engine off first.
3) High side has higher pressure with AC on so check with AC on. If nothing is found recheck just after turning off AC and engine. Sometimes the engine fan blows away the leak and the leak detector cannot find it. Preasure will still be high for a few minutes after turning off AC and engine.
4) Some leaks are more likely under low pressure. Preassure has a tendancy to cause seals to self seal. So you may want to do the oposite of the above as a second check.
5) Compressor seal is checked at the front of the clutch not the back of the clutch.
6) Electronic detector needs to be capable of R-134 if using R-134. It is a different detector than an R-12 detector.

Now you say you loosing cold air, are you sure you are loosing Freon. Are there bubbles in your sight glass. Have you put a pressure gauge on the system. What are the pressures when you fully charge the system and three days latter. Pressures should also be taken with Temperature and preferably Relative Humidity.

Preasures should be read with doors and windows open, AC on max RPM at @ 1500 to 2000. and theoretically a fan blowing on the condenser. Sight glass should also be observed at this time.

Also pressures for an R-12 charge will be different from an R-134 charge. The service manual only publishes R-12 data because R-134 was not available back then. Does anyone have a good source of numbers for a 560SL with R-134 charge.

Oh if you are replacing the evaporator you are really in the belly.

John Roncallo

[wallster]

Another way to remedy a bad a/c unit is the easiest and most effective 280 method. Simply roll down two windows and go eighty. Cools it down and no messy time consuming work.

wally

[B36TC]

You might also check the schrader valve where you fill the freon. I have seen these leak before on my Father's BMW. He almost went nuts trying to isolate the leak before he found the schrader leak.

[560slsteve]

thanks for the replys--i was rudely interupted by work--had to run a boat to charleston last week.

Anywho, i disassembled eveything up to the heater cores,and took the blower out and looked at the backside of the evaporator and eveyhting looked good. since i need the car next week of the 4th, i decided to stop, vacuum the system and go with the dye stuff to really narrow things down. i did put on a new expansion valve and drier. I am fairly sure the expansion valve was not opening at times, and there was a little stuff in the filter, but not that much for the age of the car.

after vacuuming, the thing held good vacuum for 45 minutes, then began to leak down. i charged the system , put in the UV dye, and ran it. it cooled well, and after looking with the black light in the back of the evap. with the balck light, i could see some flourescent green around the bottom, and tiny spots throughout the fins.....so i guess thats the verdict.

every place else looked fine--all the hose connections, everywhere around the compressor, etc.

so i guess after the 4th week i will take it back down--i am leaving the pass. seat out and some of the lower air ducting---i did change all the dash lights plus got the ododmeter gears replaced and working.

I think this time i will just remove everything and then take the dash off--looks like 3 bolts and that will expose everything and should be much easier.

i would appreciate any advise from anyone who has done this--plus--it looks like i have to remove the air grill from in front of the windshield to remove the heater hoses to get the heating coil out---then the evaporator shoulfd be fairly easy. i dont really understand how you remove those plastic press on things on the grill other than drilling them out somehow and replacing them--plus it loks like i have to remove the lower windshield trim.......

anyway, thanks for the advise you guys. i did get the mother of all vacuum pumps and a good set of gauges, so i guess i will have to learn all this stuff. i am pretty sure all is well if i can just keep the gas in the system. the freeze 12 stuff is really cold anyway, if it will just last.

now, before this started, the car began to miss at idle.....i changed the plugs, no dice, so i guess thats another thread....never seems to end.


thanks again. and i will be doing the windows down AC next week---not going to waste another can of gas until this thing is tight!!!!

[Roncallo]

Originally Posted by 560slsteve

thanks for the replys--i was rudely interupted by work--had to run a boat to charleston last week.

Anywho, i disassembled eveything up to the heater cores,and took the blower out and looked at the backside of the evaporator and eveyhting looked good. since i need the car next week of the 4th, i decided to stop, vacuum the system and go with the dye stuff to really narrow things down. i did put on a new expansion valve and drier. I am fairly sure the expansion valve was not opening at times, and there was a little stuff in the filter, but not that much for the age of the car.

after vacuuming, the thing held good vacuum for 45 minutes, then began to leak down. i charged the system , put in the UV dye, and ran it. it cooled well, and after looking with the black light in the back of the evap. with the balck light, i could see some flourescent green around the bottom, and tiny spots throughout the fins.....so i guess thats the verdict.

every place else looked fine--all the hose connections, everywhere around the compressor, etc.

so i guess after the 4th week i will take it back down--i am leaving the pass. seat out and some of the lower air ducting---i did change all the dash lights plus got the ododmeter gears replaced and working.

I think this time i will just remove everything and then take the dash off--looks like 3 bolts and that will expose everything and should be much easier.

i would appreciate any advise from anyone who has done this--plus--it looks like i have to remove the air grill from in front of the windshield to remove the heater hoses to get the heating coil out---then the evaporator shoulfd be fairly easy. i dont really understand how you remove those plastic press on things on the grill other than drilling them out somehow and replacing them--plus it loks like i have to remove the lower windshield trim.......

anyway, thanks for the advise you guys. i did get the mother of all vacuum pumps and a good set of gauges, so i guess i will have to learn all this stuff. i am pretty sure all is well if i can just keep the gas in the system. the freeze 12 stuff is really cold anyway, if it will just last.

now, before this started, the car began to miss at idle.....i changed the plugs, no dice, so i guess thats another thread....never seems to end.


thanks again. and i will be doing the windows down AC next week---not going to waste another can of gas until this thing is tight!!!!

Do a search on center vents. You will find alot of usefull information on taking the dash appart. Also be sure while you are doing all this work you should consider replacing at least the 2 vacume pods inside the heater box and repairing any cracks in the heater box if required. Also consider the 2 stage vacume pod for the defrost and center vent. These pods get old with age and start to fail. They are what I call $35.00 parts in a $1000.00 location.

For those front grills you have to remove the lower windshield trim piece, gently I broke a windshield removing a stuborn one. You have to drill out the plastic rivits and replace them. I'm not shure but you may be able to drive the center pin of the plastic rivet through about 1/2" and then you may be able to pull them out and pice them back together and use them over.

John Roncallo