another heater problem

[nicnet]

Hi all

Toyota Supra MkIII - 1988
White. Non-turbo.
~150k miles


I have a problem with the cabin heater.
Symptoms are:
-start car, engine warms up
-heater works fine for some time (e.g. 10 mins)
-air flow suddenly goes cool (but not cold, as in outside air cold)
-heat then comes and goes, cycling from hot to cool

also noticed:
-it often goes cool first time, when starting to drive fast (like entering motorway/freeway)
-when going from cool to hot and hot to cool, I think I can hear a vent opening/closing, inside the heating system.

The problem is not the the VSV valve- I've bypassed that as discussed elsewhere on the message board.
Although I have occasionaly heard gurgling sound in dash board, I don't think it's air trapped in heater matrix.
I have burped it a couple of times (as discussed elsewhere on the message board).
Also heat comes and goes, through the vents.
But entry/exit pipes carrying warm coolant to the matrix are both hot, so flow through the matrix seems to be good.

I think it might be one of the sensors, opening and closing a vent somewhere in the air system.
Any suggestions please?

This is quite a problem for me - this car is located in Finland, and with winter coming, it's starting to feel seriously cold.
On a related but different subject, I've read opinions saying that Supra is not a car for winter driving. I have to disagree.
Here in Finland, winter tyres are mandatory for 3 or 4 months of the year.
And with studs, I've never really had a problem, despite it being rear wheel drive.
My other car is front wheel drive Citroen Belingo (the family car - opposite end of the scale from the Supra).
It's not that much easier to drive on ice/snow then the Supra.


Nic

[abhattan]

Sounds like you still have air trapped in the system. I know you might have burpped the system already, but in these cars it can take you a while before you get all of the air out. Unless you have a coolant refill system (Snap-On), It will take a long time.

[ddmcse]

it does sound like the VSV are you sure you by passed right ?

a very low level of fluid in the radiator would produce this but i doubt this is the case

[nicnet]

for sure it's not the VSV problem - I can see the valve is constantly open, yet the air temperature coming from the vent fluctuates from hot to cool and back.

I will try burping again (have done it twice now for 20 mins), but I don't think this is the problem. If collant was having trouble flowing through the heater matrix, then surely it wouldn't go suddenly from cool to hot to cool, but rather a gradualy change in temp as flow through the matrix became slower, then quicker (for whatever reasons).

And what about the perceived change noise and change in flow rate of the air, as it changes from hot to cool and back - as I said, it sounds to me like a damper issue - perhaps the Air Mix Control Damper. You can see it on top diagram in page AC13 of TSRM:
http://www.cygnusx1.net/Supra/Librar...aspx?S=AC&P=13

I wonder how to get to that damper - perhaps keep it forced open to see if heat stays constant? (will also burp again).

Nic

[supramacist]

Burping takes hours dude.
The more incline under the nose the easier it is.

I'm wondering why no one has mentioned the heater core.
I had one go out on me and it did the temp shifting till it shucked.
Wich wasn't long after that.

You can just type n/a for non-turbo.

[nicnet]

Burping was done on a really good incline, but not for hours (20 mins max), so it could be a possibility to try again.

I'm working on the theory that it's not the heater core - mainly on the basis that I can't face taking the whole dashboard out. Naive? Perhaps.

Got another working theory, suggested in a thread over on http://toyotaownersclub.com/
Could be worn out solder joints on the heater control panel.
Took it out this evening, and re-soldered all the joints (some of them were looking a bit sad).
Put it back in, and heating was working ok, at least for the short time I tried it.
That proves nothing yet though - I need to take it out for a longer run tomorrow.

If not working ,then I'll try a longer burp (excuse me!), and also look at this air mix control servo, as I still think that's a possibility.
If still no joy, then yes, I'll have to really consider the heater core itself.

[supramacist]

Some guys spend countless hours burping the system.

Then some of us just make it routine maintenance.

Some guys say up to 5. 10. 15. hours.

Kicking the engine over, moves the air bubble around.

It's nothing to burp. Just set it up on ramps and check on it every 15 minutes and when it looks lower. Fill it up with a 50/50 mix of coolant and distilled water.

[nicnet]

Good news is that the problem is fixed:

>>> Could be worn out solder joints on the heater control panel.


It seems that this was exactly the problem. I resoldered all the joints on the unit (I suppose there's 30-50 of them), took about 10 mins.

Now the heating is steady and hot.
Also removing and putting back that unit has made the lights on the heater controls work - perhaps the leds were loose.

[supramacist]

Cool Good to know.

My heating unit acts funny the buttons like like to stay pressed down.

[dannydavi]

good job. that is good to know. my heater is not working right now.. dont think it's the same problem, but good to know for future, thanks. My problem started after i was fucking around with things dont know what i did, working fine one day and not the next, i think it was when i was messing around with my intake manifold... any suggestion, whats this "bypass the vsv" i am hearing about?