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Old 10-16-2003, 09:13 PM
300sd2000 300sd2000 is offline
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Join Date: Sep 2000
Posts: 97
by in-large the problem with heat tends to be with the monovalve. I just replaced the sleeve about 2yr ago and I think once before that....

I was having the same symptoms before, that is of inappropiate heat.

Replaced with the monovalve repair kit and everything is working fine again...I think they just wear out fairly fast. Couldn't really tell anything was wrong with the old one visibly, but the repair kit is fairly cheap so I just decided to replace it.

I have the aux water pump disconnected anyway, but it didn't really solve the problem for me...The monovalve was the culprit in this case.

If you haven't done the monovalve repair kit, its certainly worth a try and its easy to replace and much cheaper than the PBU etc.

Make sure you are getting a 12v signal (connect multimeter to connector on monovalve) and make sure you are getting 12 v when the A/C is on and cold air is supposed to be blowing...if you aren't you've probably got a bad PBU. If you are getting 12v, probably bad monovalve.

Even if you aren't getting a 12v signal and suspect the PBU is bad and don't want to spend the money, you could run a wire over from the fusebox over to the monovalve and splice it in...this is what I did before I replaced the PBU a long time ago (when I couldn't afford the PBU) and it actually worked (except couldn't automatically get heat anymore). In the winter, disconnect the connector and you always get heat.

After I bought a replacement PBU, I removed the temporary "splice" and everything is back to normal.
1) 84 300SD 285K+ Miles (Ver Calif)
2) 84 300SD 175K+ Miles (Ver Federal)
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