I'd posted earlier about this recently purchased car being flat towed behind a motor home. It's been a good memory teaser working on this thing. How quickly we forget!

I knew when I bought it I couldn't get heat out of it with the dash controls, so started tearing the dash apart yesterday.

This is one with the heater/ac control lever showing actual temperature numbers rather than hot-cold. There also appears to be a sensor on the lower dash passenger side.

The normal heat, defrost, ac vacuum functions work as they should except the heater hose mounted water valve does not move in any setting. It appears this valve should be normally open and be pulled closed when the ac is activated. Manually activating the valve makes no apparent difference. Guessing the valve is bad, as I recall that being a common problem, but that still doesn't explain why I can't get heat to blow out of the dash itself.

The heater core appears to not be plugged. The hoses on core inlet/outlet pipes heat up consistent with each other and heat up well.

I can get an electric signal to the ac compressor. Besides the fan controls and light, there are another 6 wires plugged into the control unit.

I assume this was some form of climate control system and would automatically control heat or a/c functions to maintain temp set point.

I've found a diagram for the vacuum tubes but hadn't been able to locate any trouble shooting documents for the unit itself.

Anyone have any experience with these please? I once again find myself feeling pretty stupid. Thanks in advance.

Pull the heater hoses, flush the core with a garden hose, that will tell you if you core is plugged. Relying on temp at the nipples isn't always accurate.

I used to have an 87 Diplomat but I don't remember much about the HVAC system, never had issues beyond an evaporator leak. And when the freon blows out the vent in use that was an easy one to figure out.

And when you flush the core, back-flush it (flush backwards to normal in & out). I was getting very little heat from my Durango and did this. I couldn't believe how much crap came out. And heat was like a new car after that.


Tim

Mine is an 1987, so I don't know what differences there might be. It is indeed a climate control system. The valve in the heater hose should be vacuum controlled - with the car warmed up is the hose on the back side of that valve warm?

The air door is actuated by a servo motor and not vacuum. You should hear that motor actuate as you slide the temperature control back and forth. If not, it could be a multitude of things. For me it was just the plug connection on the motor though. There was absolutely no tension anymore on the pins. To fix it I just pulled the servo motor box apart, scuffed up the pins and laid a bead of solder on them to build it up a tad. After that the plug fit snugly again and the air door started working. Good news is you can get the servo motor out without removing the air box.

If the air door not moving is your issue, let me know. I've got pictures detailing the fix I can post.

Thanks for the input! I disconnected the heater hoses and took a garden hose to the core tubes. Flows well in both directions and virtually no gunk came out of it.

Confirmed the water control valve is normally open. Put a hand vacuum pump on it and it does activate as it should. When up to temp the hoses are hot on both sides of this valve, which I guess they should be since it's normally open. No gunk apparent in the valve either.

I've heard no indication of a servo motor activating. I was wondering if there was more to this than the vacuum diaphragms since there were extra wires coming out of the control. Could you get me pointed in the right direction to find this motor please?

Thanks again guys!

For the life of me I can't find those damn pictures, nor the thread on Dippy.org. I'll keep looking - got my kids' birthday party today so stuff is crazy.

The dash pad has to come off and with it the glove box. With that removed you should have a narrow opening to see the top of the air box. The servo is bolted to the top using a single 9/32" bolt. Try messing around with the connection and see if it's lose. If I put tension on mine and actuated the switch it would work until I let go of it. The servo case itself comes apart easy enough and you lay a bead of solder on the pins to build them back up.

I'll check back later. Good luck!

Sorry for the delay, I finally found that old thread with the photos.

Check the temp slider first before digging through the dash. If it checks out with the values below then it's time to start digging. You can bench test the servo after pulling it out. I forget what pins are what though.

Hope your birthday party went well. No problem with delay here as my weekend was pretty much shot helping my kids with respective house projects. Been that way most of the summer.

Hope to get to the 5th Ave tomorrow. Gonna need heat pretty soon around here.

Looking at the pictures you were kind enough to post, can I assume the servo motor has already been removed in the first shot and the air door pivots on a vertical axis?

Thanks again. This helps a great deal.

No problem!

Yes to both. Sorry, I don't have a photo of the servo motor itself mounted to the top of the box. It's a single bolt on the top that holds it in place.

Attached is a top down of the air box removed from the car from when I replaced the core. This should give you a good frame of reference of where to find the servo once you have the dash pad removed.

It sounds like the servo that Mark is talking about. Sometimes you can get them unstuck by moving the control from full hot to full cold. does the vents the air comes out change when you presss the different buttons?
It can also be the vacuum lines in the dash for the controls have gotten britle and no longer do what they are supposed to anymore but I think usually when that happens it defaults to defrost.
You know chances are good it's not the heater core because like you said in your first post both the inlet and outlet hoses get hot.

Thanks again for the input, suggestions and photos.

I worked on the car again. I was starting to think there was something different about an 88 model until I realized there was a black plastic 'sock' stuffed in above the heater box, and below the felt type insulation that's visible in the previously posted pictures. Being black, it hid things pretty well.

I had the car running and blower going while working so I would know quickly if anything changed. The plastic was really stuffed in place, all around the motor housing. As I pulled it out (to get better access) the heat started blowing.

I played with the motor connector to see if I could get it to act up again, but no change; nice heat keeps blowing. All vacuum controls work properly and the connector plug for the vacuum tubes is in very good shape. Moving the temp lever does appear to cause some modulation on the amount of heat.

I'm going to use the car with the dash partially disassembled for a couple days to see if anything changes. Can't say it's fixed, but I feel much better about the situation now.

I really appreciate the guidance!

what was this "sock" touching/blocking, that you now have heat ? what does this thing look like ?

Here's the piece I was describing. It was stuffed on top of and all around the motor housing. There's foam inside of it.

I don't know if it was pure coincidence or if this thing was causing some stress on the assembly.

I wasn't sure if someone had been into this thing before me or not. One of the mounting tabs on the hvac control was broken off (no loose pieces found), otherwise if it had been apart, someone put it back together with reasonable care.

Tried again today and things are still working!

would it be hard to stuff back in place to see if the heat quit ? i know it's better to quit while you are ahead, but it does make me wonder. sounds like maybe that thing was deforming the case somewhat, causing the air door[s] to jam up ?

I'm glad it's working! I totally forgot about that piece of insulation being stuffed around the assembly. It's been a few years since I had this apart.

Before you button it back up, if you haven't already, apply a downward force on the connector and slide the temperate control to the other side. If it works then do it again with an upward force. If that checks out then I guess just chalk it up to gremlins.

I don't think I put that insulation back in either.