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Old 08-03-2005, 06:21 PM
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Join Date: Jul 2005
Posts: 20
A/C problems

i recharged my AC in my 1985 300D and when i get in the car to turn the AC on, all it does is blow out hot air, ill switch the controls and i can hear the compressor turning on and off but i only feel hot hot air blowing out. is it the monovalve? and if it is, where can i get that monovalve rebuild kit? thanks a bunch

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Old 08-03-2005, 06:25 PM
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Join Date: Jul 2004
Location: PHX and SLC, Middle East, Asia
Posts: 302
get the rebuild kit here or another parts supplier. Yes, that sounds like the monovalve. You can confim it by clamping shut the supply to the heater core on the passenger side rear of the engine, then running the ac for a while.
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Old 08-03-2005, 06:50 PM
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Before you buy a monovalve o/h kit, make sure that the monovalve is getting electrical power. It is closed electrically; it will open to the maximum heat position if power is not present. The connector on the valve itself is often the culprit.
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Old 08-03-2005, 09:45 PM
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Don't pinch off the hose, you will ruin it.

Let the car cool off then remove the four screws atop the monovalve and lift it up. If it is flooded above the diaphragm it will have to be rebuilt. You can get the kit by clicking on fastlane above or if in a hurry at your local dealer.

Good luck,
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Old 08-04-2005, 09:17 PM
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when i removed the four screws and lifted the monovalve, coolant started to spill out underneath where the monovalve goes in, i only pulled the monovalve a coule millimeters and then pushed it back down to stop the coolant from spilling. does this means it is flooded and i have to rebuild the monovalve? do i just pull it out and let it drain? thanks
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Old 08-05-2005, 01:26 AM
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anyone? this is new car to me and im not used to it so please help?
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Old 08-05-2005, 02:10 AM
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Join Date: Sep 2004
Posts: 9,087
Thumbs up

If it's the original one from '85, it's probably had it.
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.
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Old 08-05-2005, 09:03 AM
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When you remove the plate on top of the monovalve it should be dry ABOVE the rubber diaphragm. If it is not then the diaphragm is leaking and must be replaced.

Good luck,
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Old 08-06-2005, 07:28 PM
Join Date: Jan 2005
Location: Silver Spring, Maryland, and Larkspur, Colorado
Posts: 123

Just want to chime in with dittos to Larry's advice. You may also want to SEARCH on my name FRANKNBENZ. I had a similar problem, suspected the monovalve, turned out to be oxydation on the monovalve electrical posts-to-the-plug connection. I defer to other, more expereienced members, but I would:
1. Pull the monovalve by removing the four screws. Inspect the diaphram for holes and whether it can still hang ten, fully seated on the rim.
2. Check the length of travel of the axel extension. Without damagingthe basket screen, gently pull it about 10 mm or so. You should see the diaphram stretch and can check for holes, etc.
3. Ensure the little C clip is still on the end of this assembly.
4. If all this stuff checks out, do the two electrical terminals. I used a spray can (with one of those tiny diameter long red straws) and shot the terminals, waited, then gently cleaned them. Dittos with the INSIDE contacts on the connector plug.

Hey, no panic. These members bailed me out more than they know. Chill, the fix is pretty simple and cheap. If you need them, I can open one of mine up and take some photos to send along. Good luck. Welome to the club.


85 300D 270,000
85 300D 210,000
94 E320 170,000

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