Climate Control Unit: Replace?

[Gil]

I've got a 300CD with a few vaccum problems, hard shifting, etc.

The vacuum valves in the doors, fuel door, 5 servos (behind the console) and starter switch were all replaced, and most of the problems are fixed.

However, I've still got:

Hard shifts. The brake booster line has a broken nipple leading to the tranny; replacement of this may take care of the hard shifts (or not?)

No heat to the floorboards. Checked the vaccum from the servos, and zip, nada, nothing in any setting coming out of the hoses or diaphragms. Since they're both (passenger and driver side vents) non operational, the CCU may be at fault, or so my dealer suggests (then again, why wouldn't he, at nearly $400 bucks installed!).

I've got very little patience for chasing down vaccum leaks, but installing a new CCU is so simple a monkey could do it.

Would replacing the CCU have any bearing at all on the floor vents? The electronics are quite primative, leading me to wonder how often this part fails. Is there anyone who rebuilds these Carter-era electronic wonders? I noticed there is a core charge from people who sell new units.

Also, I have the typical "no heat in the center vents" situation, though some in this forum say it's normal (MB designed) not to have heat come from those vents.

The fan and temp settings work ok. AC is out, but that's for another reason.

Occasionally, the little buttons used to jump ship when one was pressed, but I took care of that with some clips used inside the unit.

Basically, I'd hate to blow a serious chunk of change on one of these for no reason. Any ideas out there?

Thanks

Gil

[autozen]

Since you commented on the little buttons leaving their posts, I'm assuming you have the newer style system with the mono valve. The old Chrysler had more obedient buttons. It could be the ECU or the mono valve or the push button unit or a vacuum problem. You are going to have to do some diagnostics or spend a bundle on an Easter egg hunt. I don't know where to begin to help you on the computer. Perhaps one of the other techs has written up a procedure.

Good luck,
Peter

[AuctorEcclesiae]

Hello Gil:

I can definitely tell you that there is no heat that comes out of the center vents, and this is totally normal. These vents usually go closed in the winter time, or if you would like some fresh air while driving with the heat on, open the damper a tad.

Hope this is helpful.

Take care,
Michael.

[Gil]

I hadn't considered the mono valve possibility. I thought that since I had heat, the mono valve was ok. Maybe not?

Yes, it's a newer style (1984 300CD) CCU, though I never knew the older ones were made by CHrysler. Is that what you meant?

By ECU, what are you referring to? Same as the CCU?

Are CCU failures common?

Thanks for the suggestions, I'll be doing my own easter egg hunt this weekend.

Gil

[autozen]

Gil,
Take the 4 screws out of the top of the mono valve, pullout the slug, and check the diaphragm.If it's torn, buy a replacement kit.

Chrysler sold the earlier ACC system to MB. It was about the same quality as the cruise control system Ford sold them in the early 70s.

Sorry. Yes. Climate Control Unit is samy same as Electronic Control Unit. CCU=ECU Yes, they fail, but so do the other components I mentioned.

Peter

[Gil]

OK,

I blocked off the hoses and took off the top of the mono valve. After I got the slug out, I checked the diaphragm for cracks and such. Everything looked fine. The screen didn't have much crud in it either. In fact, the whole mono valve doesn't look all that old.

I never had trouble with heat to the cabin itself, just getting it to the floorboards.

Does the mono valve affect the interior distribution?

Anyway, it looks ok. I really hope it doesn't come back to the CCU replacement.

Thanks again. I'll entertain any other theories out there, too.

Gil

[kerry]

Checking the vacuum actuator for the footwell vents is pretty easy. Remove the trim panel under the driver's dash. The actuator for the footwell vents is just to the right of the accelerator behind the ductwork. Hook a Mityvac directly to the actuator and pull a vacuum. If it holds a vacuum, its ok. Then put the mityvac on the line going to the actuator, warm up the car, turn on the heat and see if vacuum is getting down there to the actuator. It there's no vacuum getting to the actuator it is either the switchover valve or the CC unit itself or a leak in the lines connecting those things.
My footwell vents weren't working and it was the rubber connecting hose right at the actuator itself. Fix took a couple of minutes once I traced it down.
While it could be an electrical problem, with all the vacuum lines in that system I'd put initial focus on a vacuum problem.