94 E320 some heat, most times... - PeachParts Mercedes-Benz Forum

wolf_walker · #1 09-18-2017, 10:27 AM

It finally got cool enough I noticed our E320 seems to have some heat, but not full, from the dash vents most of the time regardless of the temp wheel position. I've caught it behaving normally a few times, and the air outlet seems to change normally depending on the temp wheel position, it just stays a bit warm on full cold. Which might be part of my marginal AC performance all summer

. Any diag to be done on this thing or just start replacing likely suspects? It seems to work as it should otherwise, I replaced the sample motor last spring.

Diseasel300 · #2 09-18-2017, 10:56 AM

Start by testing the A/C performance. See if the return lines to the compressor are cold and sweaty with the temp wheel set to full cold. If not, you know you likely have A/C problems.

Next suspect is the monovalve (or duo valve depending on your model). They can fail where they stay open. My SDL did this and it was miserable... New cartridge solved my issue. The cartridge looked fine, but the shaft had gotten rough. Just enough that it wouldn't pull closed...

wolf_walker · #3 09-18-2017, 11:02 AM

AC performance is so-so at best, it does cool but not very well, it's not low on freon, the pressures are right and I've tried running them lower and higher, PO had the compressor replaced twice in a short time which makes me think there is a restriction or the expansion valve is bad or the parts store compressor is bad or some such, but it does cool and seems to regulate temp as it should when it's cool enough to not need full-ac.

My first guess was the monovalve too, is there such a thing as a rebuild kit for them? It seems to work at least some since it's able to go from little heat to lot of heat, is there a blend door that might not be closing?

JimFreeh · #4 09-18-2017, 12:00 PM

When on full cold, the coolant flow should be off.

Any heat coming out of the vents when on full cold indicates flow.

Flow occurs when the monovalve fails to close.
Failure to close is either bad monovalve or no signal to the valve.
Default is full flow, so signal has to be present for monvalve to close.

Way to check:

Check for 12V at the valve, feel hoses to see if there is heat, which indicates flow, in the hoses.

Re A/C performance:

W124s are not fantastic A/C performers from the factory......Since your car had R134a originally, it has a better chance with the improved condenser and fual fan setup.

If you've already had several compressors replaced, there is reason to suspect that the problem lies elsewhere. Unfortunately, that means a thorough rehash is necessary.

If the compressor is providing a good high/low pressure, then I'd evacuate the system, then back flush as much as you can, to see if there is something blocking the evap or condenser tubes. Then replace the expansion valve (next to the brake booster) with a new one, button back up, evacuate, then replace the freon.

Jim

wolf_walker · #5 09-18-2017, 12:04 PM

Thanks Jim, my thoughts exactly on the AC, I think I'll get away with putting it off till spring if fall does it's thing on time here. 10/4 on the monovalve, is it possible to rebuild those things if they are leaking coolant by internally?

Diseasel300 · #6 09-18-2017, 01:49 PM

There is a cartridge available from the forum sponsor. Cost of the cartridge kit is something like $35. Worth a try before getting too carried away with the A/C system. If the heat is stuck on, the A/C performance is going to be crap!

wolf_walker · #7 09-18-2017, 02:42 PM

Unless I'm blind all the kits for these are for the pre-93 one. The valve is 93-95 e class looks like.