AC not very cold
 

Just had my ac serviced but, although blowing cool it is not cold. Shop says there may be a flap not opening fully as as freon is ok. Any ideas where that flap is and how I can prop it open. Not wanting to keep pumping money into this as I want to sell it. Car is 1985 380SL.

Generally MB uses the heater to increase temps while the AC is on. If both of your heater hoses are hot when the AC is on, the heater valve may be leaking or what controls it not working.

Also, in my opinion, the AC in 1980's German cars was not very effective even when new.
I know many people with '80's Mercedes' and Porsche's who have thrown thousands at their cars trying to make them blow as cold as an '80's GM car. Ain't gonna happen.
A buyer who is familiar with this vintage of Benz will understand. Someone who is not is going to be disappointed.

Well, I have to disagree. I am the original owner of a 1981 300SD and the AC has always been great; has worked just as I suspect the MB engineers made it with the R4 condenser. While I understand that folks who have converted to R134a have been disappointed, I have always had great cooling from the original, as designed, system with R12 (what we used to call freon).

Agree tyl. I had my '83 converted to R134. It cools o.k if you start the ac before the car gets too hot in the interior. Takes a long time to catch up from hot. The conversion was done correctly replacing compressor, expansion valve, dryer, hoses and o-rings.

I am told that replacing the condenser with a good cross-flow version will fix it completely. Klima has one for $245. Thinking about it.

After a run, feel the heater hoses. If both are hot you have hot water flow fighting the AC.

On all my cars regardless of brand, I add a ball valve to positively shut off heater water flow. On a car without a heater valve, you end up having a hot heater core in the passenger compartment not to mention air leaking around the diverter doors.

I use a 3/8" pipe thread valve and a 6" long piece of pipe cut in half. The OD of 3/8" pipe is slightly larger than 5/8 and slightly smaller than 3/4" so it works with both common sizes of heater hose.

The W123 (my '83) has a heater valve, the monovalve. It is designed to regulate by switching on/off allowing the heater to regulate the ac temperature. Worked pretty good with the original R4. Works o.k. but less good with the R134 system.

My ex-560SL still had the original R4 system that worked fine after 25 years.

These systems were designed to operate with r12 not r134a which requires larger condenser surface area and operates at higher pressures.

The switch to using r134a in their r12 systems appears to fully correlate to the rash of shortened compressor life and diminished cooling experienced by folks who made that switch. Don't ask me how i know.

The cure is simple: Use r12 or, more economical and environmentally responsible, a hydrocarbon blend such as offered by Duracool or Envirosafe which matches r12 performance.

WDBCB20; Look at Post 5 again. I replaced EVERYTHING except the condenser. I understand that replacing the existing condenser with a cross-flow is the final and ultimate step. Maybe this Winter although the system as presently configured works albeit with a struggle.

Yes, I looked at that post in astonishment why you would:
1. Tear out a perfectly good condenser
2. Replace it at a cost of $275 + labor (unless DIY)
3. Install a new drier + labor and draw a vacuum again

Only to still end up with a system straining a compressor not designed for r134 lukewarmly (pun intended) endorsed by Klima as follows:

"This product is a non-OEM system modification which has not been evaluated or approved by the vehicle manufacturer. Product is installed at your own risk. Legal Disclaimer: This product is intended for off-road use only. "

.

Older condensers are fin and tube, this isn't as efficient as a cross flow where the tubes are flat and each tube had 5 ish internal passages. ( Think single tube depth engine radiator Vs multi depth. )

Leaving a fin and tube unit in the car will actually lead to higher system pressures because of poor heat flow. A patch for a fin and tube would be to jumper / add a pressure switch to the aux electric fan for better air flow.

To repeat; I HAVE changed the compressor to an R134-compatible version. The reason for spending the money/effort on the condenser is as stated above by 97 SL.

Is it possible for you to post a pic or two of your bypass setup? Curious to see it in the engine compartment.