a/c hisses, doesnt work - PeachParts Mercedes-Benz Forum

Grdenko · #1 11-11-2003, 08:07 PM

a couple days ago, my a/c worked great, now it makes a hissing sound from the center vent area and doesnt cool at all.

could this be a vacuum leak? how would the a/c act if it wasnt getting vacuum?

or am i just out of refridgerant?

thanks

The Warden · #2 11-11-2003, 08:15 PM

Does the blower work?

If not, could be a fuse.

Just a thought...good luck!

Grdenko · #3 11-11-2003, 08:20 PM

blower works, so does the heater, but it wont blow cold at all. i would think if it ran out of refridgerant it would gradually work less and less. but it was working fine not long ago.

#4 11-14-2003, 07:24 AM

The hissing very well could be a vacuum line broken or disconnected.

Turn on the a/c max for five minutes, then check the sight glass. If there are no bubbles in the sight glass, then the refrigeration portion is working fine. You should make sure the compressor clutch is engaging before checking the sight glass.

Good luck,

Zoonhollis · #5 11-14-2003, 11:24 AM

Also: make sure the connection on the top of the monovalve is good.

leathermang · #6 11-14-2003, 07:44 PM

If there is NO refrigerant the sight glass will NOT show bubbles... that is why the sight glass ALONE can only do so much in terms of trouble shooting...
Put some gauges on it and turn it on.... that will tell you a lot of things about your situation.

Grdenko · #7 11-19-2003, 07:16 PM

ok, the compressor is engaging, but i cant find the sight glass. any idea where it would be on my car.

the other night i also noticed that the lights for my a/c controls are not coming on. all of my other console and inst. lights are coming on though.

i checked all of the fuses after that, and theyre all good.

thanks for the help

ps:those guys in 'tech help' are a bunch of jerks. the first one told me to do a search (like i hadnt already) and the second guy told me my car wasnt worth the $250 it would cost to get a shop to find the leak! then he called my car a 300E! what an insult!

#8 11-20-2003, 04:05 AM

Quote:

and the second guy told me my car wasnt worth the $250 it would cost to get a shop to find the leak!

And this guys opinion isnt worth s#%t!!!

I dont care if youre driving a puke green gremlin, if you love your car its worth the world to you. All the blood, sweat and tears(and $$$) we put into keeping our older cars going obviusly show how much we care for them. Ive got a friend who put over 5k into what seemed to be a real junker, definatly more than its monetary value, but he has the most fun with his car than anyone i know. I cant believe someone who calls himself a car "tech" can have this opinion. Maybe his idea of caring for a car is plugging it in and waiting for the codes.

josh

Grdenko · #9 11-21-2003, 03:35 PM

thanks for the moral support.

im really starting to think that its not freon though.

i just noticed that at highway speeds, with the windows closed and the a/c off air from the outside is coming through all of the vents, alot of it, really fast. its like i have the a/c blower its so fast.

i tried turning the a/c on and putting on low fan and then i hit the recirc switch, but it still was coming from the outside just as fast, and i didnt hear the outside air flap close when i hit the switch.

as i understand it, the vacuum controls the opening and closing of all of the flaps to all of the vents in the a/c duct system.

i think that the outside air flap is open all of the way even when the a/c is turned on instead of its normal %80 closed, so the a/c cant cool all of that outside air enough to be effective. this hissing seemed to start when i was trying to fix some other vacuum problems in my car, so i may have pulled something loose.

that would not explain why the lights in the a/c controls would go out though, but it may explain the hissing. the empty freon theory would not explain why the lights went out either.

Does the a/c normally hiss when the freon is out?? somebody told me it did but that was the same guy that called my car a 300E!

i would really like to find out where the sight glass is, ill go through my service manuals a/c wiring and vacuum diagrams this weekend and find out where the sight glass is too.

i really hope that it ISNT the vacuum because that would mean that i have to take the dash off, or pay a shop to. ($$$)

does this vacuum theory make any sense?
does the a/c hiss when its out of freon?
what would cause the lights for the a/c controls to go out?

so many questions....

i really appreciate all the help so far
thanks

Rick Miley · #10 11-21-2003, 03:47 PM

Grdenko, ever since you started to mess with the EGR, your entire vacuum system has been seriously screwed up. The same vacuum system supplies the EGR, ARV, transmission, and climate control, but not the door locks in your model. I think all these troubles explain why that line you found plugged was like that in the first place.

The vacuum problem would not explain the lights, and it may or may not explain the hissing.

In the 1987 300E that I once owned, the sight glass was behind the driver's side headlight. Just follow the A/C lines until you find the receiver/drier (the cannister looking thing). It will be there.

Grdenko · #11 11-21-2003, 07:44 PM

i appreciate it, but this afternoon, after i got tired of guessing, i took it into my favorite shop and had it checked out, both the vacuum and the a/c.

nothing but bad news. they loaded it up with R12 and checked for leaks and it looks like my evaporator is shot. theyre going to load it up to 200 psi (normal pressure when the compressor is running) and check again to be sure. apparently the hight pressure makes it quite obvious.

so much for my nonsense 'theories'. although, we did find the vacuum leak that was keeping the flap from closing, but ill go into that more on my EGR thread.

thanks for all of your help and advice.

leathermang · #12 11-21-2003, 08:02 PM

That is the legit way to check a system... some people try using vacuum... but sometimes , since that backloads the seals, one will leak in vacuum... but not in use....

Rick Miley · #13 11-21-2003, 08:31 PM

After 2 compressors, a condenser, and finally a failed evaporator, I sold my 300E on ebay. Hope you have better luck with yours!

Grdenko · #14 11-21-2003, 10:23 PM

gee, thats reassuring!

thanks