jaguare22

Hello, thanks for helping a newbie! 1998 CLK320 the A/C is NOT cold and given Kentucky Summers, that ain't good A/C worked fine last two summers and winter defrosts seemed ok too.

I read other posts how to pull the sensor reading (thanks for that) and are:
Sensor 1 (Inside Temp): 92
Sensor 2 (Outside Temp): 73
Sensor 3 (Left Heater Core Temp): 151
Sensor 4 (Right Heater Core Temp): 91
Sensor 5 (Evaporator Temp): 187
Sensor 6 (Engine Coolant Temp): 186
Sensor 7 (Refrigerant Pressure): 5
Sensor 8 (Refrigerant Temp): 99

So OK, the left and right Heater Core Temps are a little wonky, but it seems it really needs a charge based on #7 and #5. I hook up a fresh can of R134a and the can gauge says it is pretty full already, but it still takes just a little bit (can gets a little cold too) then suddenly pegs the gauge red. I disconnect & reconnect, make sure A/C is on and blowing and turning (yep, I know it is a variable system) and sure enough it says 100 psi, in the red zone.

I rerun the diagnostics and the #7 is now at 7 (up from 5), but still warm air. This confirms it took a little.

Just to be sure for #3&#4, I clean the DouValve, but it looks good inside, and afterwards I see no significant temp change left to right.

I have re-run the diagnostics on startup, after a 45 minute drive, etc, and they are always about the same, plus or minus some outside temp changes.

so oh great wise benz folks, I assume I have a high side blockage. Any clue where to start? I'm really sweating this one (pun intended).

MarcusF

Compared to mine, the refrigerant pressure looks low. If I start the car with the AC on, and don't touch the gas, I see 15. I see 7 while driving and 11 or 12 while waiting at lights.

Assuming the condenser isn't covered in crud, I'd check the expansion valve. The valve may be stuck. If so, on the high side expect less than 200 PSI if the valve is stuck open or 400+ and climbing until the pressure switch stops the compressor if stuck closed. Here's a link to how to do an AC tuneup, which includes how cleaning the condenser coils.

jaguare22

Thanks Marcus! So it turns out, the problem was more basic. The A/C clutch wire was only hanging on by two strands right at the compressor connector So when I watched it I could see the clutch working, but under any load it was dropping out. I found it by checking the system multiple days, and eventually I noticed it was NOT always turning. I went to check power at the connector to confirm the senors and such were working and it fell apart in my hand! Fixed the wire 4 days ago and it has been blowing cold ever since.

thanks to all!

exhaustgases

That is strange with such low pressure. And if the day comes, word of advice, don't just add refrigerant, fix the leak first.