Air Conditioning Time - PeachParts Mercedes-Benz Forum

Litton · #1 04-26-2004, 06:04 PM

Well, it's getting that time of the year again (at least in Tucson) to start wanting to use the old AC. Now mine has never been used since I bought the car and I know it wasn't blowing cold so today I took it to the shop for a checkup. Took 2 cans of R12 and and some dye to look for leaks.

Still not blowing real cold and the shop says it looks like the expansion valve is sticking closed. One of the pressures is too low. Apparently they do that some times from lack of use. There is a high tech fix....a swift rap alongside the head to get it's attention, but we it seems to be in hiding. I assume it's tucked away down behind the panels and stuff.

Any other thoughts.

Tomguy · #2 04-26-2004, 06:10 PM

Would this be the piece with the glass window on it to look for bubbles? (I don't know AC too well), if so it's in front of the rad (evaporator?) on the lower left side.

Litton · #3 04-26-2004, 07:23 PM

Nope, that's the filter dryer. The giz-a-dichi will have a capillary tube and a blub that is near the condensor or evaporator (the thing that gets cold) and the body is conected to the line from the compressor side that makes cold. It has a tiny valve in it that causes a pressure drop in the freon line and turns it into a gas.....or something like that. Anyway this bulb thing senses the temperature of the thing that gets cold and causes the valve to to open or close thereby telling how much freon liquid to convert to freon gas and suck up heat.

Or something like that.

cth350 · #4 04-26-2004, 07:54 PM

There is an electric gizmo that has a capilary tube. It's the switch on the dash with the green "swoosh". Under that switch is a little access plate that will let you get back there. -CTH

Tom Drew · #5 04-26-2004, 08:02 PM

Your expansion valve on the 280SE 4.5 is located inside the AC evaporator box under the passenger side dash up against the firewall. Not fun to get to.... I just removed it on my car along with 95% of the dashboard to access & remove the heater box to repair a non-functioning blower motor. I though I knew what pain was - I was wrong!
You do have to discharge the AC system and do a fair amount of dash disassembly to get the evaporator box out from under the dash to open it up to access the expansion valve. The procedure is outlined in the "Passenger Cars Starting 1968 Series 108 - 109 - 111 - 113" Service Manual.
If I ever meet the guy who designed this HVAC system....

Litton · #6 04-26-2004, 08:17 PM

Oh My, all that just to hit it with a wrench? No straight shot where one could use a long extension like a pool cue?

I really only need to beat it not amuputate.

Tom Drew · #7 04-26-2004, 09:56 PM

Unfortunately, no, if you need to physically hit the expansion valve to solve the problem. The valve and evaporator coil are completely encased in a hard plastic box, with only two openings for entry and exit air, which are connected to ductwork inside the car. And after you've spent the time to remove the evaporator box you will want to install a new valve anyway, because believe me you will not want to go through the removal process a second time.
Maybe someone else with AC experience knows of another way to "shock" the expansion valve into operation.
As a side note, some of the earlier 108's had the expansion valve located right on the firewall, but those of us with the 4.5L cars will have to put up with this situation. Just be glad you don't have to replace your heater blower motor! Then we can really talk. Good luck!