hobiecat

Something else to check...... There are two vacuum controlled solenoids on the right side that control the
mixing flaps. Those can also fail..... Not sure how to test them, but you could at least check that they are getting vacuum?

Don't forget the other temperature sensor located under the hood. It's right at the entrance to the
fresh air intake on the passenger side. A failure there will also screw things up.

DarylJ

Reading all of the suggestions about flaps, fans, thermistors, etc. still leads me back to the same conclusion: If the heater control valve works, you shouldn't have that much heat in there to blow around, regardless of what else might be wrong with flaps and other inside items. Standard redneck practice when you have this issue is to put a (residential plumbing) valve in the line and shut it off when it's not cold out.

Mark944na86

I had at look at those, but they are for flaps that direct air out of of the various vents, rather than anything to do with temp control. So if one of those failed, the symptom would be that you couldn't change vent selection -- and that's working fine on my car. If it's a flap failure, it's going to be flap 3 and/or 4 with my symptoms, I think.
Good idea -- I'll see if I can locate that one and test it as well.

Yummybud924

I want to know too lol.

for me it blows hot all the time whether turned to cold or hot and when I shut the fan off it's still blowing hot air out the vents.

it gets freakin hot sometimes I have to open the windows even when it's raining or i'm sweating.

in the summer it sucks real bad as not only does the air conditioning not work it's blowing hot air in the summer heat lol.

passengers in my car always complain about why it's so hot.

Mark944na86

Warm, not hot.

I did a bit of extra testing while driving today. It was cool outside, so I left the aircon off, and just put the fans on "2". Warm air coming out of the vents.

How warm? I did a quick experiment -- turned the temp control **** from all the way full "cold" to full "hot".

Phew! Now that's hot air!

OK, so what I was getting was warm, not hot air. In other words, a mixture via flap 3 being partially open, but not fully open. So it's inaccurate to say I have a "constant full heat" condition. More like an incomplete heat shutoff condition.

To extend the experiement, I turned the temp **** all the way back to full "cold". Fortunately, the temp mixing flap complied, and surprisingly, to a cooler level than it was when I started. Not quite full cold, but closer.

Got to my destination, turned the engine off, after about 15-20 mins, started up again.

This time driving home I was getting full cold. Which is good, but not great, because obviously it's all a bit flakey.

But it does prove the temp mixer flap is not stuck, and the electric motor controllling it is working.

It's a bit of a mystery as to why it sometimes closes the flap completely, and other times leaves it partially open. Hmmmm...

Any thoughts?

hobiecat

If you turned the **** from full heat back to cold and you felt it get "cooler" than before, maybe the temperature switch (****) on the control unit is faulty.

See if you can find someone with a "working" control unit, swap it out and see what happens. That'll be considerably easier than tearing into the hvac unit to
get to that mixer flap/mechanism.

Mark944na86

Well, that's a good thought -- if the potentiometer track (I assume temp control is a pot) is dirty, and it's not reading the correct resistance for that position, then the system could simply be complying to a faulty directive. I could try some pot clean in there and see if that helps.

Alternatively, the temp mixing flap may just be a bit sticky from lack of use (truth is, I hardly ever have the temp on anything except full cold). Maybe giving it a bit of "exercise" will help free things up. I'd like to get some silicone in there to lube it, but might be tricky...

JohnKoaWood

1 thought, 1 suggestion

Thought: Things up here normaly don't get sticky from lack of use....

Suggestion: Here in the states we can get "electrical connector cleaner" hose out the control head with some of the same (aerosol can type stuff)... See if this cleans it out...

Mark944na86

I'm not quite sure what to make of that, but I'll take it at face value!

Yeah, it's called something fancy like that here too, I just call it pot cleaner 'cause I'm lazy. "Electrical contact cleaner" rings a bell. Main thing is it's a solvent that doesn't melt plastics, and doesn't leave a residue. Good stuff... I use it mainly to fix noisy pots on my electric guitars...

Mark944na86

Actually, looking at the photos, I bet those electric motors are servo motors... which makes a lot of sense for this application, actually.

Servos change and hold their position depending on a signal voltage input (reference votage). Change the voltage up and down, the servos motors changes it's position up and down. Makes it easy to build analog control circuits.

That should make it fairly straightforward debugging the system with a simple multimeter -- if you can get access to the servos. E.g., check for the reference voltage changing, does the motor change position? Yes, servo motor good/ no, servo bad, etc. Does changing the temp setting switch on the panel result in a change in measured reference voltage at the servo? Yes, switch & panel (probably) good/ no, bad switch & panel, etc.

Also makes it possible to check for inconsistent output from the same switch position...

theykallmekem

this has happened to my 89 n/a, but it blew hot air randomly from start up to driving, it really got like a sauna in there !!

in the end, it was just a bad heater control valve, cost like 30$. but since yours is fairly new .... >_>

Mark944na86

hmmm... did you do anything else except change the heater valve? According to eniac (see above), a bad one _shouldn't_ create a "heat always on" condition by itself...

theykallmekem

that is what the mechanic said when i asked him to check it out, and he just charged me an hours of labour, and the part (heat control valve). not sure what else he did, but im sure he did more if it shouldnt create that "heat always on" by itself... times like this i wish i did it my self >_>


btw it was an 86, stupid number pad lol

Mark944na86

Mechanics tend to mention what they've done, rather than not mention what they've done. If he just said he replaced the valve, I would be surprised if that wasn't the extent of it.

Interesting.

Mark944na86

Old thread, but just to report back -- I finally just replaced the Heater Control Valve, and that solved my "persistent warmth" problems. Eniac's advice is off-the-mark in this thread -- I suspect if he had no heater valve, and he wasn't getting heat, then it was something else that was preventing flow through his heater core. My heater control valve was operating under vacuum, but not sealing properly.

Simple fix, but I was thrown because (I believed) the heater control valve had been replaced fairly recently. Inspecting the part I replaced, I now no longer believe that to be true...

Just in case anyone else is dealing with this.