ACC or Vacuum Pods?
 

Hello Everyone. If you've any insight on this condition please help me out. It just snowed 14 inches here and I need some heat!:eek2:

My 1984 300D has recently developed an issue in the climate control reality. Everything is fine with it when I first start the car. But about 5-10 minutes later all the vents close. Defrost is the same, and the only setting that reopens them is AC with the temp set to cold. But soon after I switch the temp back to warm the vents close up again. Most of the time turning off the car for a few minutes will reset the vent flaps to open. However upon restart if the car is warm the vents will close sooner than before. :dizzy2:

What the hell is going on? Do you have any clues? My searching has been fruitless and now the weather demands a solution.

Thanks for your time.

Jeff

Sounds like a burned circuit on the ACC board. Mine was acting odd like that a while back. I could here is clicking inside.

Try pulling the ACC unit out and then pull the circuit board out and look for any burned spot. You should be able to resolder any spots that are burned.

How is the vacuum at the pods?

There is a thread on here that has all sorts of diagrams in the DIY Links. There are also vacuum switchover valves that are electrically operated that divert vacuum to open or close flaps. IIRC they get thier electric signal from the ccu based on what button is pushed.

What type of troubleshooting have you done so far?

so far my troubleshooting has been limited to testing out the various functions of the ACC to find the various results. This is my only car and an overloaded schedule has kept me from tearing into yet.

There is no constant clicking, although there may have been a click when the vents close - i heard one once but couldn't tell you for sure if it happens everytime or not.

Today I'll pull the ACC and check the solders all around.

Thanks for your input.

JEff

Here is the link to the diagrams. They are in B/W but are very helpful.

http://www.peachparts.com/shopforum/diesel-discussion/105297-vacuum-diagrams.html?highlight=vacuum+diagram

which vents are u talking about. Side vents and legroom vents should be working in EC heat mode, none in the center and a little in the windshield.

I cannt believe the defrost vent closes. The design of the defrost is such that if vacuum is lost it will go to full open. I assume the fan continues to run? I'm thinking the CCU is faulty or the MONO valve is failed internally.

yes, all the vents close. defrost, sides, under the seats, by the feet. All trickle a little bit of heat and you can hear the fan going full bore.

why they are open at first and then close is particularly peculiar to me.

thanks for all the responses. I have recently gone through the ACC checking all solders and there were a few to resolder. I'm not sure yet if that will make a difference but I'll find out tomorrow when I go for a highway drive.

And thanks for the vacuum diagram link especially.

Jeff

main air flap and/or its components not working(pod or switchover valve).

solder work did not change a thing.
luckily the sun is out.

thanks for the vacuum diagrams - i'll be using them shortly.

i'm looking at these vacuum diagrams and wondering - how much am i going to have to tear into the dash to reach the main flap pod and switchover valve, or all of them for that matter.

unlikely cure
 

sometime last night, as the question of what the hell was going on with my heater was bouncing around the back of my mind, a strange thought/feeling came to me, and i wondered "I wonder if I'm low on coolant?"

So this morning I went out and checked - sure enough I was considerably low. Though the car showed no overheating signs or anything like that, apparently I've a leak of some sort.

Then I started her up and let her warm, and after driving up and down some hills to get the air out I discovered that Viola- I have air coming out of the vents.

Low coolant = vents close? WTF?

Regardless, thanks for your time. I hope this outcome helps someone out there sooner or later.

try disconnecting the aux water pump and see if problem goes away.aux pump could be seized and overloading the CC cicuit:)

damnedest thing, later the same day i'd filled the coolant and magically had working vents again my brushes on my alternator wore out:mad: . i replaced the voltage regulator the next day and . . . the vent flap commenced to closing again:confused: .

i'll check out the aux water pump theory next