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

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 06-20-2004, 03:10 PM
JamesStein's Avatar
Registered User
 
Join Date: Apr 2004
Location: Tallahassee, FL
Posts: 586
Symptoms of a bad monovalve?

Does this sound like the monovalve?


Car starts.. AC works great until the car is stopped for a short period of time. 30-60 minutes. Then the AC blows hot air for a variable amount of time. Usually 15 -30 minutes in traffic. It will cool down quicker if you get up to speed.

Am I on the right track here?
__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.
Reply With Quote
  #2  
Old 06-20-2004, 09:10 PM
vwbuge's Avatar
Registered User
 
Join Date: Sep 2001
Location: Johnstown, Pennsylvania
Posts: 2,101
I am not entirely sure that a bad monovalve has anything to do with the A/C.
__________________
'85 300SD (formerly california emissions)
'02 Jeep Grand Cherokee Limited
'04 VW Passat W8 (6spd manual) SOLD!!
'68/'69 Empi Imp body on '65 Beetle pan
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'72 Triumph T100R
'70 Yamaha R5 Rat Bike
Reply With Quote
  #3  
Old 06-20-2004, 10:25 PM
LarryBible
Guest
 
Posts: n/a
The monovalve has everything to do with the a/c. The refrigeration portion of the a/c system runs all the time. The temperature is regulated by the amount of heat that is added to the cooled air (I know, it sounds very inefficient.)

That said, what you describe does not sound like a problematic monovalve. The monovalve typically fails by leaking and flowing coolant to the heater all the time. The symptoms of that are sweat and then smelly clothes.

What your problem does sound like is an inoperative cabin temp sensor. This is typically not the sensor itself, but simply the tube that supplies air across the sensor.

Remove the glove box and you will see a pipe running horizontally behind the glove box that goes toward the temp sensor that is below the small grill in the center of the dash. See if there is a hose leading from the pipe to the sensor. It was originally a foam hose and disintegrates after a few years.

If the hose is gone, your first inclination will be to replace the hose with a piece of garden hose, heater hose, plastic hose or some other substitute. Don't do that! The foam hose conducted virtually NO temperature through the hose material. Being foam it insulated any heat that may travel through the material of the hose so that the air sample was accurate.

Go to Home Depot and get some foam pipe insulation. This is sold for insulating plumbing pipes in the winter to prevent freeze up. Cut a length of the foam hose and slip in place.

Good luck,
Reply With Quote
  #4  
Old 06-21-2004, 09:03 AM
Registered User
 
Join Date: Dec 2002
Location: RI shore
Posts: 2,937
When my monovalve failed, I had similar symptoms. Of course, in CT it doesn't get used much. What I remember very well was that in the winter I would get no heat until the engine was partly warmed up (about 60C) and I SHUT OFF THE ENGINE AND RESTARTED. Then I would have heat as long as the dash thermostat called for it. I hate to admit it, but I wqas so busy at the time that I lived with it for a whole year. Finally replaced the monovalve, no problems since.....Current to the valve CLOSES it when it is operating properly, but if it is failing, the valve may not close. You could try this....Disconnect the wire to the circulator (if you have one, so there is no chance of it deadheading) and clamp the hose between the monovalve and heater core with a flat clamp (I used a vise-grip type) to shut off the flow. See if that changes anything. Just make sure your hose is in good shape (nice and flexible, not hard or cracked) before you clamp it.
Reply With Quote
  #5  
Old 06-21-2004, 09:59 AM
JamesStein's Avatar
Registered User
 
Join Date: Apr 2004
Location: Tallahassee, FL
Posts: 586
I'm pretty sure the foam hose is intact. I'm at the office right now and can't verify. Both mine and my wifes cars are having AC issues and I'm not sure if I actually checked hers or mine.

I suppose I should stop trying to troubleshoot 2 identical systems with different problems at the same time.
__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.
Reply With Quote
  #6  
Old 06-21-2004, 02:16 PM
JamesStein's Avatar
Registered User
 
Join Date: Apr 2004
Location: Tallahassee, FL
Posts: 586
Just got a call from my wife. She says it appears to be related to acceleration as well.

The AC started cooling and she came up behind someone slowing down on a hill so she braked. Then climbing up the hill the AC cut out and never recovered.
__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.
Reply With Quote
  #7  
Old 06-21-2004, 03:39 PM
Registered User
 
Join Date: Dec 2002
Location: RI shore
Posts: 2,937
that may just be incidental. Check other things in the system before you go too far. At a fast idle (1500RPM) windows open MAX A/C on (temp switch MINIMIZED), blower on highest setting, see that A/C clutch goes on and stays on. Auxiliary fan should come on and off with temperature switch. Also, there is a pressure switch which will cut out the clutch if the pressure is marginal. You can check that with a jumper wire and a gauge if necessary to see if a problem is charge or the switch, etc, etc. At least the system is cycling on and off, so the troubleshooting shouldn,t be too bad. Good luck
Reply With Quote
  #8  
Old 06-23-2004, 11:59 PM
JamesStein's Avatar
Registered User
 
Join Date: Apr 2004
Location: Tallahassee, FL
Posts: 586
Well 2 things I've found..

#1 AC belt is stretched.. to the point that I cannot tighten it enough to even begin to make it tight. I am actually shocked that the compressor is even running its so loose. I've order a new belt to resolve that issue.

#2 in-car temp sensor is was missing some parts and not even connected properly. The hose was just haing free in the dash and the PO had replaced the foam section with some heater hose. I'll remedy that as soon as I can get to Lowes. Also the part that the hose actually connects to on the sensor is gone.. I'm hoping its just hanging at a low point on the wiring harness, but I really didn't feel like dropping the driver side kick panel. I just stole the one off my car for now since the AC in it is majorly wacked.

I imagine the biggest part of the problem is that belt.
__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.
Reply With Quote
Reply

Bookmarks

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 01:17 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page