New CCU, no power to monovalve, heat only
 

I've got an 83 300TD wagon, and I recently installed a ProgRama CCU (after re-soldering my old one with zero success). Everything was wonderful after that for about a month. Heat worked, as did the cold. But now suddenly there's no power at the monovalve connections, only hot air comes out of the vents, and sometimes the blower won't come on. I'm assuming I've got at least a few esoteric problems happening here, but I ruled out the blower brushes as it worked great until now. I was really hoping the spendy rebuilt CCU would do the trick! Any thoughts are mighty appreciated. Oh, and yes, all the fuses are new and un-burned.

I saw on this forum that the programa requires you to check the monovalve or otherwise the warranty is void.

So I would check your monovalve and see if that didnt fail. Then I would check your temperature sensors to see they are operating. Some of the devices maybe drawing too much and fired some circuitry. Did you amp draw of the blower motor and the recirualtion pump?

When I had my '81 the wires in the monovalve connector came loose. Try opening the connector and resoldering the wires. Also remove the CCU and check the wire from the monvalve to the CCU it is on the right side CCU connector. Take a continuity tester and check the wire.

Also check the wiring to the aux water pump If it is bad, it will draw enough current to blow out the CCU. Do a search on splicing a fuse into this circuit as a safeguard

Yes. Put a 1 amp fuse into the black lead wire going to the Auxilliary water pump to protect your CCU.

thanks everyone, this forum is great! Going to look at things tomorrow, will report back with any findings.

X2 on the monovalve plug, little squeeze on the connector tubes and all was well again. Just be very careful messing with the monovalve connector, if you short the 12V to ground, bye bye CCU

OK, it seems that the blower motor is drawing too much juice, which is (maybe?) making the #8 fuse get really hot, and perhaps has fried both my old CCU and the new one (?). The fuse gets hot only when blower is on high fan setting. The aux water pump appears to be functioning properly, and there actually is power to the monovalve. I found a strange sticker on the blower housing, a local electrical auto parts supplier's warranty seal. I called them and they claimed that they have not sold parts for 83's for many years, which is potentially strange because the sticker looks brand-new and holographic. Maybe the stickers have been that way since the Reagan administration, I have no idea. Anyway, I suspect the blower to be some kind of aftermarket thing, if that is possible, or at least defective, and I'm getting another from a parts yard tomorrow, and another ProgRama CCU as well. First I'll replace the blower and see if the #8 fuse gets hot on either fan setting, then check monovalve and aux water pump function. If all that is cool, then the new CCU goes in. We shall see what happens.

An update:

I got a junkyard fan. Although it looks like an earlier version, it came out of a 123. It spun easily, but caused the fuse to get hot anyway. So I pulled my original fan apart and replaced the brushes and oiled the bearing, put it back in the car. The fuse still gets hot to the touch on the high fan setting only. The air flow thru the vents is considerably weaker than it was pre-fan-rebuild.

I put a one amp fuse in the black wire leading to the aux water pump to protect the new CCU.

I've read elsewhere on the forum that the MB blower fuse shunt kit is meant for w124's, and that it should not be used on 123's. Does anyone have experience with this on a 123? And would it be a good idea to put one in, or just spring ofr a brand new fan?