79 300D heater blowing cold air

[Island300D]

Hi all,
A while of searching revealed nothing too clear to me so I will start a thread and seek some advice. My beautiful 300D has the infamous climate system everyone hates and that never works. Fine, it defaults to only the defrost working, which here in the NW has worked fine for me for the past 5 years. But just this week, my defrost setting has stopped blowing hot air. The fan still works the same, but only cold air comes out.

Now I'm aware of basic heater functioning, so while on the road I immediately became fixated on my temperature gauge fearing I had somehow drained all my coolant on the road, but my temperature sat at the usual temp.

So something is preventing the hot coolant from getting to the radiator for the heater. My search revealed something about a monovalve, but it's not clear that my 79 has one. Any advice on the simple cheap way to get this working again? When I am rich someday I would like to spend the 1,000 on the solid state system that will run the whole HVAC as it should work, but for now, just getting defrost to work would be great! Thanks for any help.

[Doktor Bert]

Your 1979 does not have a Monovalve.

Check your #3 and #9 fuses in the fuse block, as they influence the climate control. Also, many W116's had an in-line (glass) fuse holder in the fuse box just for the auxillary water pump.

Check the hoses on both sides of the CC servo for heat. Also, listen to ascertain of the servo is running (parking) when you turn the switch off.

Report back....there is quite a diagnostic procedure for that system....and you can find the entire thing right here....Robert

[Island300D]

Thanks Doctor Bert, will do. Since the whole climate control system doesn't work, and only the defrost mode did, I didn't think there was anything electronic about the coolant flow through the system. I realize a work around here since I've given up hope on ever fixing the climate system would be to simply bypass the whole works and direct plumb the coolant hoses to the heater radiator, but first I will check the fuses you mention and see if there is an easier fix.

And by the way, the PO had spent like a grand to have the factory climate system redone right before I bought her a few years back, and it worked for a month or two before dying. Everything ever said about what a disastrous design it is does not come close, and yet the rest of the car is bullet proof. Go figure.

I'll report back when I check the things you mention. Thanks again.

[sjh]

Originally Posted by Doktor Bert

Your 1979 does not have a Monovalve.

Check your #3 and #9 fuses in the fuse block, as they influence the climate control. Also, many W116's had an in-line (glass) fuse holder in the fuse box just for the auxillary water pump.

Check the hoses on both sides of the CC servo for heat. Also, listen to ascertain of the servo is running (parking) when you turn the switch off.

Report back....there is quite a diagnostic procedure for that system....and you can find the entire thing right here....Robert

Is a '79 300D a w116?

You sure there is no monovalve?

My '81 300D had one.

heck, take a picture of your firewall in the vicinity of the battery.

.

[charmalu]

Since Chrysler developed this system MB decided to use. here is a manual
from the Chrysler Imperial club.

http://www.imperialclub.com/Repair/Lit/Master/281/index.htm

Charlie

[Doktor Bert]

Originally Posted by sjh

Is a '79 300D a w116?

You sure there is no monovalve?

My '81 300D had one.

heck, take a picture of your firewall in the vicinity of the battery.

.

I am confused....I know he posted '300D' which should be a 123, but he mentioned the evil servo, so maybe he can clarify????

I answered based on the assumption it was a W116...Sorry....Robert

[Doktor Bert]

Originally Posted by Island300D

Thanks Doctor Bert, will do. Since the whole climate control system doesn't work, and only the defrost mode did, I didn't think there was anything electronic about the coolant flow through the system. I realize a work around here since I've given up hope on ever fixing the climate system would be to simply bypass the whole works and direct plumb the coolant hoses to the heater radiator, but first I will check the fuses you mention and see if there is an easier fix.

And by the way, the PO had spent like a grand to have the factory climate system redone right before I bought her a few years back, and it worked for a month or two before dying. Everything ever said about what a disastrous design it is does not come close, and yet the rest of the car is bullet proof. Go figure.

I'll report back when I check the things you mention. Thanks again.

The system isn't as bad as you think. I've been using mine for over 10 years now and the only problem I have experienced was a frozen auxilliary water pump and a shorted A/C low pressure switch that would blow the #3 and #9 fuses anytime it was switched from full hot on the temp wheel to DEF or a cold temp wheel setting.

Other than that, all the sensors test within range, I replaced the notoriously rotten aspirator hose to the in car tem sender and run nothing but R-12.

My wife is driving the car for her Mary Kay business and leaves it running (locked) while making deliveries so the lipstick doesn't melt. It runs for 12 hours a day sometimes, most of it idling with the A/C on and it produces 44°F in the center vent all the time. I leave my pocket thermometer in the vent.

The auxilliary fan cycles on and off based on a signal from the switch in the top of the drier and the temp wheel will produce smooth transition between heat and cold.

I'm using one of the dreaded 'Mantis' CC servos, which actually worked better than the new one I got from George Murphy. Of course, George made it right when I sent it back without any questions, but the mantis is smoother and faster in transitional operation, so I kept it.

If you follow the diagnostic procedure, you will quickly find what is wrong with the system...Robert

[Island300D]

Hi all,
My 300D is a 78 and is a W123. The fuses are all fine for my system and here are a few pictures under my hood. You may notice that I have removed the belt for the AC since the climate system didn't work anyway.

I don't see anything monovalve like along the firewall of the engine, and all the guts to the climate system seem to be on the front passenger side. That is where hot coolant goes into, and doesn't come out. Something in there is not letting the coolant go through the heating radiator. Could that be the location of the monovalve on mine? Hope the photos got attached properly.

And, I had thought my car has the evil servo from Chrysler, but the link provided is to a 1971 system which is surely too old to have been used in my 78 W123. So what is my system anyway!!! Wish the damn thing worked.

Thanks for the help!

[Doktor Bert]

You have the Chysler-designed CCII servo, the same basic syatm as I have on my 1978 W116. This system will not have a Monovalve. The CCII system has been around since the late 1960s...Robert

[Island300D]

That's what I thought, and I guess that is the bad news. Glad you've had good luck with yours Robert. Probably less luck than good repair jobs. Robert, you mention following a diagnostic procedure, which I would like to do. Where is it? I don't think I saw it on a review of the manual posted above on this thread.

And again, I had read that our system was designed to default when otherwise broken to having the defrost work, since it is most critical, but even that has stopped working on mine. Though the blower blows.

With winter approaching here in the NW, it is critical I get the defrost working here by September or the car sits.

[Doktor Bert]

I worked on these a lot when I was with the MBZ dealer, because nobody else would touch them. They are not as mysterious as people think and a lot less complicated than GM's 'Comfortron' system was.