84 300SD Climate Control Test Procedure?

[DieselGuy]

Hello,

Summer is starting to really bare down out here. The temperature has gotten up to 106 degrees these past few days. Last week the Automatic Climate Control in my '84 300SD refused to blow air out of the center vents. Air only came out of the side and defrost vents. I check vacuum to the ACC system and it was 1.5 in. mg. Well I was forced to dismantle the center dash and console as both under-dash panels. I checked the bank of switch-over valves marked 1 thru 6. As it turned out, the vacuum element that controls the defrost vent was leaking vacuum. So I went to the dealer and got a new element to the tune of $44.50. It's located to the left of the glove box, right next to the on/off swith of the glove box. It's pink with 2 diaphrams.

Now since everything is open and visible and easily testable, I'd like to know what is the test procedure for the ACC functionality? With this crazy summer heat now, I want to make sure the system is performing at peak efficiency before I button everything up.

Here are some things I have observed from my '84 300sd:

1: The flap directly behind the glove box (recirculation flap?) swings towards the engine compartment when the ACC is turned off. With the ACC in either the EC or normal mode, the flap swings towards the glove box but leaves a gap of 1".

2: Air comes out of the defroster vents in any cooling mode. Just a little air though. According to the manual, "just enough air" should come out only in heating mode. it should remain complete closed in any other mode(except defrost of course). I checked the switch-over valves going to this vacuum element and the valve labeled 1 closes the defrost vent approx. 80% of the way and the valve labeled 3 closes it the rest of the way until it's completely shut. No matter what mode, temp setting, or fan speed I can't get valve "3" to activate and close the defrost vent all the way.

3: Valve 3 also controls another vacuum element that opens a flap inside the air box. Since I can't get the valve to open, this flap remains shut. I did pull the valve and it functions when voltage is applied to it.

4: Pushbutton unit PCB was resoldered due to cracks on the joints. So I'm sure it's functioning correctly. Also the vacuum going to the ACC system is now holding 18 in. mg. since I replaced the faulty vacuum element.

Sorry for the long post... I just wanted to provide adequate info for the specific questions I have. I'd love to know how to test the system and figure out what actuator opens and when. Thanks in advance!

Nolan

[Jack500]

To properly perform all the ACC circuit tests, you need to get the ACC tech. manual from the dealer. It costs around $30 and gives the step by step procedures.

It sounds as though your recirculating air flap located to the rear of the glove box is malfunctioning. When the flap is fully forward toward the engine it is closed and does not allow outside air into the car. The two vacuum switches that control this flap are two stage like the one you replaced for the defrost. In the AC mode (button c in the middle of pushbutton) the flap should be about 3/16 on an inch from fully closed which is considered 80% recirculated air. The flap should move to 100% closed with the temp. dial set to minimum. In all other modes including economy mode (button d) the flap should be fully open toward the glove box. Hope this helps.