SL/R129: AC Compressor doesn't stop spinning...
Thread Starter
Newbie
Joined: Mar 2018
Posts: 7
Likes: 1
From: San Francisco
1992 300SL Manual 5-Sp, 1993 300TE 4-Matic, 1995 Mazda Miata, 2006 Land Rover LR3, 1994 Saab 9000 Ae
AC Compressor doesn't stop spinning...
1992 300SL with single-zone automatic climate control
I searched throughout the Mercedes forums and could not find anyone with similar symptoms with my AC system and compressor. Here are the symptoms...
-Climate control blows cold air, even when I had the "EC" button pushed or if I turn the climate control off by pressing the "0" button. The compressor stays engaged.
-When I turn the temp wheel on hot, the HVAC system blows warm air, but the compressor still spins and I'm sure it is still cooling, maybe freezing, the evaporator because as soon as I turn the temp dial down to the blue zone, the cold air blows out of the vents immediately.
-When I unplug the compressor (electric plug), the compressor does stop spinning.
-The compressor does disengage and stop spinning periodically for short bursts, but then engages again and stays on.
A month or so ago, I added a little bit of R134 to the system (already converted from R12) and it cooled the system down a to acceptable cooling levels and acceptable PSI for the ambient temp. The system functioned fine for a couple of months. I'm not sure if this is related to my issues. Does anyone have any ideas as to why my compressor remains engaged when it should not be?
Thanks in advance for the help!!
I searched throughout the Mercedes forums and could not find anyone with similar symptoms with my AC system and compressor. Here are the symptoms...
-Climate control blows cold air, even when I had the "EC" button pushed or if I turn the climate control off by pressing the "0" button. The compressor stays engaged.
-When I turn the temp wheel on hot, the HVAC system blows warm air, but the compressor still spins and I'm sure it is still cooling, maybe freezing, the evaporator because as soon as I turn the temp dial down to the blue zone, the cold air blows out of the vents immediately.
-When I unplug the compressor (electric plug), the compressor does stop spinning.
-The compressor does disengage and stop spinning periodically for short bursts, but then engages again and stays on.
A month or so ago, I added a little bit of R134 to the system (already converted from R12) and it cooled the system down a to acceptable cooling levels and acceptable PSI for the ambient temp. The system functioned fine for a couple of months. I'm not sure if this is related to my issues. Does anyone have any ideas as to why my compressor remains engaged when it should not be?
Thanks in advance for the help!!
Thread Starter
Newbie
Joined: Mar 2018
Posts: 7
Likes: 1
From: San Francisco
1992 300SL Manual 5-Sp, 1993 300TE 4-Matic, 1995 Mazda Miata, 2006 Land Rover LR3, 1994 Saab 9000 Ae
Problem Solved
Just thought I'd post a follow up in case anyone else has this issue...
I was able to get the compressor to stop engaging constantly when I evacuated and refilled by AC. The compressor now disengages when I press the "EC" button. I'm suspecting that I may have had too much refrigerant pressure in the system from when I filled it.
I was able to get the compressor to stop engaging constantly when I evacuated and refilled by AC. The compressor now disengages when I press the "EC" button. I'm suspecting that I may have had too much refrigerant pressure in the system from when I filled it.
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
On a '96 or earlier car the compressor engages in response to the evaporator temperature. In retrospect, your system was probably under-filled and unable to drive the evaporator temperature low enough to trigger disengagement of the compressor.
Thread Starter
Newbie
Joined: Mar 2018
Posts: 7
Likes: 1
From: San Francisco
1992 300SL Manual 5-Sp, 1993 300TE 4-Matic, 1995 Mazda Miata, 2006 Land Rover LR3, 1994 Saab 9000 Ae
Thanks for the input @bobterry99. Shouldn't the EC button on the climate control unit disengage the compressor regardless of the evap temp? My compressor would not disengage even when the EC button was pushed. i even tried a different CCU...
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
Your problem was wiring, a pair of faulty in-dash controllers, a stuck clutch, or a faulty ESCM module. If the system persists in working perfectly, then this is a bizarre coincidence.
