AC sytem starting to blow warmer air? - PeachParts Mercedes-Benz Forum

timreid · #1 07-27-2003, 01:22 PM

The AC system on my 400E is starting to blow warmer air. Ambient temp 85F
I checked the system by disconnecting/connecting pressure switch, and I saw a few bubbles just for a couple seconds. I took a pressure reading on the low side and it was 35psi, and fluctuated higher as the system cycled. The air coming out of center vent goes slowly down to 55F, but then goes to 63F,and back to 55F, the temperature control was set to max air and the windows open. Thanks for any ideas.
timreid, enjoy your drive

sixto · #2 07-27-2003, 06:05 PM

Is the air from the side vents slightly cooler than the air from the center vents? Is there a trickle of warm air from the defrost vents? Could be a leaky monovalve.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

timreid · #3 07-27-2003, 06:39 PM

sixto, I went to check, and air temp is the same for the side and center vents, however the temp now only goes down to 67-69F.
And there a trickle of the cool air coming from the defroster vent in either the normal or bi-level setting? Do you believe it is the monovalve.

timreid

#4 07-28-2003, 07:41 AM

First off, you really need to monitor both low AND high side pressure and watch the sight glass.

Secondly warm air does not necessarily indicate a problem with the refrigeration portion of the climate control system. The temp is regulated via coolant flow to the heater core. To isolate whether or not the coolant flow is the problem, temporarily block flow to the heater core somehow. If blocking coolant flow cools the vent temps then that is the portion that you need to troubleshoot.

Good luck,

csnow · #5 07-28-2003, 09:38 AM

I won't pretend to know for sure, but it seems that one might be able to limit the flow to the heater core by disconnecting the power to the mono valve? Of course, you can always crimp the hoses (carefully).