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1990 300TE
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63 Posts
Discussion Starter #1
A little recent history for my 1990TE. Last fall, had a slight coolant leak from water pump area. Took it to a fairly good indie, and he said that an additive may resolve issue. I agreed, and needless to say, it was a failure. New water pump, new radiator, new idler assembly and belt installed and cooling was great and no leaks. Unfortunately, no heat either. Removed plunger from monovalve and heat restored for winter, unregulated, but tolerable. Plunger installed this Spring and heat shut off, which is OK for summer use. Installed new monovalve recently, and still no heat. Have 12V between 2 terminals on monovalve plug with key on and in heat mode. While driving, I played with temp control knob stop to stop several times and heat came on. None next day, went to defrost, heat on, then off in reg mode and defrost mode. Think I should belooking at reman CCU? Also, noticed in auto EC mode, blower fan kicks on well before car actually warms up. Sorry about long post, but I need to get this resolved before really cold weather kicks in.
 

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Registered
1990 300TE
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63 Posts
Discussion Starter #2
Update

Been trying to get a handle on this. In defrost, it usually generates heat. If I switch to EC, it will put out heat until temp is reached, then will not cycle back on. Fan blows clod air. I can hear clicking sound from battery area, which I assume is the duovalve. Turn on defrost, it heats up again. New duovalve installed recently. Does this sound like a climate control unit issue? Is there something else I should look at? Any help much appreciated.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,376 Posts
Replace ALL fuses in the fuseblock with the updated copper core type first, including the strip fuse on the strut tower.

Also look at the vacuum connections at the yellow check valves next to the brake booster and make sure the valves work.

After that, start suspecting CCU. The clicking sound might be coming from the KLIMA relay or the OVP relay behind the battery.
 

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1990 300TE
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63 Posts
Discussion Starter #4
Thanks sbaert..I will order the new fuses and check the lines and valves over the weekend. Wierd problem, and the intermittent nature is frustrating
 
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