w126 monovalve question
 

Will a malfunctioning monovalve on a 420sel cause the a/c to be less efficient?

YES, but fresh air bleeding into the system will do the same thing. Also the W126 chassis has a flap in the heater box that blocks air-flow thru the heater core when the system is in the A/C mode. Again vacuum leaks will allow this to stay open as well!

MB Doc,

Thanks for the reply. The reason I specified the monovalve is the heater does not blow hot at all. I was wondering if I can wait until winter or Should I fix the monovalve now, since it does effect the a/c I guess now is the answer.

MB doc,
I have a similar problem with my 350SD. The A/C takes about 5 min. to kick on once the car is started and it shuts off frequently. When the A/C actually is blowing it makes a noise that sounds like the engine is nocking but it stops when I shut off the A/C. What could this be and if it is a vacuum leak what is the best way to find and fix it.
Thanks for the help!!!!!!

sdbenz:

Low charge (hopefully) or bad compressor. A good compressor will vibrate some, but definite knocking noises are internal damage or a bad clutch (note that a leaking compressor shaft seal will cause the rubber in the clutch to fail -- operation is then erratic and noisy as the friction plate is loose).

On the W126 monovalve, pull it and check. It's up by the firewall in the heater hose, four small screws holding down a plastic cover. Pull the valve out (solenoid winding comes off). If the rubber boot is swollen or cracked, replace. If there is any sign of corrosion, you probably have had coolant leaking into the solenoid, and you may need to replace the coil as well.

A leaking monovalve will result in poor cooling as there is heat in the heater core all the time, reguardless of flap position. I would also test for vac leaks -- not closing the recirc flaps will make the car slow to cool off.

Peter

What is the easiest way to test for a vacuum leak?
Thanks

Use a hand vacuum pump and attach it to the vacuum circuit you want to test. Pump up a vacuum and see if it holds it.