Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

LinkBack Thread Tools Display Modes
Old 04-21-2003, 03:31 AM
Registered User
Join Date: Jan 2003
Posts: 211
Air conditioning - always high and cold/high hot

1985 (CA) 300TDT wagon. AC was converted to 134. Coldness was just ok. But alway blew high/cold, no matter what temp dial said (MIN or whatever). Changed monovalve element AND checked connection to AUX water pump. Did not check to see if pump turns. Pin connector had been soaked with oil as was pump. cleaned pump, and pins - put back together. Now I get all heat (adjustable with dial) but no cold air. As before when all I had was cold (before monovalve repair) lots of air came out of defrost vents - top of dash. Now with heat - similar air pattern. Can I be certain that AUX pump works? Can crud (oil) on pin connectors cause high amp draw on ACC - frying it? Again with GREAT heat - is pump okay? Was the new heat a combo of monovalve AND cleaning pins? And maybe the ACC is still not okay? Thanks, Steve

Reply With Quote
Old 04-21-2003, 07:51 AM
Posts: n/a
If you have solid heat, the problem is more likely related to the monovalve than the aux pump. The monovalve failing causes heat all the time, not cold all the time.

Squeeze block the hose leading to the monovalve and see if you again make cold air. If so, pull the top off the monovalve and see if it is flooded. If you don't make cold air with it blocked, check the a/c charge.

Good luck,
Reply With Quote
Old 04-21-2003, 10:06 AM
gsxr's Avatar
Join Date: Aug 2001
Location: USA
Posts: 8,102
If you never get air out of the center vents, it's possible the vacuum pod diaphragm has failed. Or you may have other leaks in the ACC vacuum system, as the "default" position is air coming out the defrost vents (cold or hot).

If you can turn the heat off, your monovalve is probably OK. I'd suspect your pushbutton unit, as after 15+ years the 123 p/b units are failing more & more often - they get cranky at first, then get worse. The "aux" pump does NOTHING except keep hot coolant pushed through the heater core at idle - so forget looking at that unless you're complaining about lack of heat at long stop lights.

Is the A/C compressor turning on? If so, you probably have *some* charge in there. Wouldn't hurt to buy the R-134a recharge kit that includes a gauge, and pop that on the low side hose - the reading will tell you if your system is charged or not.

Good luck,
Boise, ID

Check out my website photos, documents, and movies!
Reply With Quote
Old 04-22-2003, 01:13 AM
Registered User
Join Date: Jan 2003
Posts: 211
You think the (new) monovalve insert is defective? I changed that on Saturday prior to the "No Heat" situation. Now it seems that I can get (very) hot air all the time (no matter what the temp dial says), and I get cool air only if I'm lucky. Question - will hot air "take over" if ac (charge) is low and compressor is not running? I have not checked this yet. Thanks again. I did say "cool" air.

Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 04:40 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page