I posted this in the Body/Interior forum, but I haven't gotten any responses... maybe I'll have better luck here.

I was having a problem w/ the vent setting in my '88 TA -- when it was warm out, the air would come out of the defroster vent rather than the vents near the middle of the dash. After posting in here about it, we determined that the heater controls were leaking -- more specifically, the selector valve on the back of the heater controls. My dad had a heater control unit from my sister's '86 IROC, so I just took the valves out of that and hooked them up to my unit. Now my vent works just fine -- but I don't have any heat! No matter what position the slider is in, it feels like it's set to full cold.

The cable from the temp slider is properly connected -- I even pulled down the pass side hush panel and I can see that the cable is properly attached at both ends and moves thru its travel just as it should. My coolant is full, and the hoses going in and coming out of the heater control valve under the hood are both hot. There is also vaccuum going into the heater control valve.

My heat worked just fine before I fixed the vent problem, so this is almost certainly related to that. The only other thing I can think of is the 2nd valve -- there's 2 vaccuum valves on the back of the unit. 1 controls whether vent, heater, or defroster is selected. I'm not sure what the other valve does, but I replaced it anyway (I figured if 1 failed, the other probably wouldn't be far behind). Does this other valve have anything to do w/ temp?

 

anybody?

 

The other one is for the heater control valve.

 

replacing the valves might not fix it because you might have a leak on the tubes themselves where they connect to those valves. that will cause air to only exit the defrost (which is a default ) or cause the heater control valve not to function... visual appearance may look alright, but they get dry and after time lose the ability to seal.

 

Well I guess I haven't fixed anything yet... over the weekend, I had the same problem w/ the vent not coming on as I did before. On the other hand, I got my heat to work... sometimes. I've found that unplugging the vaccuum line to the heater control valve and plugging the line gives me the most reliable vent/heat control.

So... is this a vaccuum leak somewhere in the system? If both sets of lines are leaking where they connect to the heater controls, could that account for these symptoms? Why do I have heat more often when the heater control valve is unplugged then when it's plugged in? Grr... I hate intermittent problems... u never know if u've actually fixed anything until the next time it goes out

 

Some heater control valves are "negative"; that is, they're open with no vacuum, and they close off when vacuum is applied. If that's the case with your switch, but the valve you have is "positive" (opens with vacuum) then you'll have heater core flow only when the door is completely closed. The valve in the control head, and the water valve under the hood, need to have the same discipline.

You can just look through the catalog at the parts store and figure out which logic you need, according to whether you have vacuum when the control is set to full cold or when it's calling for heat.

 

Yeah, that's what I figured... except that even the heater control valve unplugged, I sometimes have heat and sometimes don't. There must be more than 1 thing that determines if u get heat or not.

 

I've been thinking about this and it makes sense. But before I pull my dash apart again, do u think it would work to put some belt dressing on the rubber fitting that connects the vaccuum tubes to the valves on the heater controls? I was thinking that might soften the rubber enough to allow it to seal.

If that doesn't work, I suppose I'll have to replace the vaccuum lines in the dash... any idea what needs to be done to do that?

 

Before doing anything with the dash, I'd suggest starting the car, and checking to see if you have vacuum on the line that goes to the heater core (the white one) when the slider is at full cold, or when it's halfway up, or both, or neither.

 

I've already done that... it seems to have vaccuum at all settings from cold to hot.

 

OK... then you must have a "negative" valve (no heat = valve closed, vacuum all the time keeping it closed = valve closes with vacuum); and the little valve on the AC control head must be defective as well, since it's supposed to have vacuum either when calling for heat or when not calling for heat, but not both.

 

it's been tried before (not always successful) to use vaseline on those tubes by applying it with a q-tip to the inside of those tubes... if you go to replace that "tube harness", you'll be doing some work on your dash to get to all of it. i have to do mine eventually. anyhow, the way i fixed mine (for now) was to separate all those vacuum lines from that junction on that switch and re-attach them individually and secure with a small zip-tie. sounds ghetto, i know, but can't be seen and is functional for now. another option would be to buy one of those replacement vacuum harnesses and splice it into the existing tubes instead of tearing half the dash apart. what i mean by splicing it, is using those vacuum tube splices. that way you can put a new connector up on the switch and use your existing vacuum tubes. just make sure you mark everything before you take it all apart.

KAM

 

Yeah I heard about the Vaseline trick, and that it wasn't always successful. That's why I was trying to think of something else that might soften the rubber and make a more permanent fix. But I don't know if the rubber of a belt is similar enough to the rubber of the vaccuum fittings for the belt dressing to be effective. I guess the only way to know is to try it...

That's also a good idea about the zip ties. I may end up doing that if the belt dressing doesn't work.