Randomtask2

iTrader: (1)

Ok hello again everybody. I don't know why my firebird will not cooperate. One thing i am not is a parts changer. I Love diagnosis. So my thermostat housing gasket was leaking upon the purchase of this car. So I decided to replace the thermostat and gasket. Decided on the reusable mr gasket thermostat housing gasket. and a napa thermostat. Then figured while i got the cooling system semi drained. Might as well. Do the heater control valve. Water pump is working just fine. flowing nicely. I was blown away that didn't fix it. So i replaced the last part I know fails in these. The heater core. Now the heat only worked slightly, in this car upon me purchasing it for about 2 days. So with fresh coolant. No air pockets anywhere. new thermostat and it opens like clockwork at 180 degrees, new heater control valve. And now as of today new heater core. And still no heat. At this point I am completely speechless on what to do next. So if anyone has any information. Please i could really use it. Thanks for reading this guys.

DynoDave43

iTrader: (11)

Well, if all else is good, I think I'd have to wonder about the control head.

If it's vacuum powered, do you have a hand vacuum pump that you can use to actuate the valve with the car warmed up and running?

Randomtask2

iTrader: (1)

Oh sorry I completely forgot to mention. It has vacuum going to it. And it is sucking just fine.This is why im completely stumped. About the most basic thing. lol

Randomtask2

iTrader: (1)

But no I dont have a vacuum pump. I will look into this. Its a good recommendation.

Randomtask2

iTrader: (1)

Ok, so the vacuum is working on that line going to the heater control valve. But it is very weak. So i took off another vacuum line with a stronger vacuum. And heat worked for a little and stopped. So i disconnected it. And the heat was blowing hot like hot hot. with it disconnected. But when hooked up heater control valve to vacuum it gets cold. Now your guess is as good as mine. lol I just did this right after your said it. Well now im completely shocked. You were along the right lines.

DynoDave43

iTrader: (11)

Excellent. Sounds like you've narrowed it down quite a bit.

I guess I'd dig into the dash at this point. Check that vac. harness form the head to the valve. If it holds a vacuum, then I would guess the problem has to be in the head.

They are known to wear. There's a thread or two around here on how to rebuild them at home.

Randomtask2

iTrader: (1)

Yes I'm most definitely appreciative that you guided me in the right direction. I figured as long as theirs vacuum going to it. That it's fine. But it would seem that isn't true. Thank you.

a62belair

Follow the heat control cable to underneath the dash in front of the passenger seat. See if the arm is connected to the heater flap. This was my problem- the arm was broken in two. fixed with JB weld- not I have heat all the time, when needed.

Randomtask2

iTrader: (1)

Oh no need. Problem was solved right after this post was posted. For some reason the solution was it doesn't like vacuum to the Heater control valve so I blocked the vacuum line and have hot heat. Probably have a defective Heater control valve.

OrangeBird

iTrader: (1)

No sir , what you have is a perfectly functioning heater control valve , and a failure in your control head . Thing is , your heater control valve turns on the heat when there is NO vacuum ! Yes indeed , the "default" position of the valve is "on" , which is why your removal of the vacuum line has provided hot coolant to the heater core .

Reason ? In a failure of any part of the system to hold vacuum , the heat/defrost defaults to defrost only , with the heater control valve wide open . This is so the defroster will still work regardless of loss of vacuum signal and the safety issues of a fogged up windshield are averted in this way . If your control head is sending vacuum , even just a little bit of it , to the control valve while the heat lever is set to hot , well then it's a defective control head because Max. heat setting must result in no vacuum to the valve in order for hot coolant to make it to the heater core .


If you search around here some , you'll find that the vacuum control valve in the control head has a common failure where the two parts of it separate and the usual symptom is a hissing from it , especially when changing lever positions , like going from heat to A/C or from vent only to heat directed to the floor or defrost vents . This vacuum leakage usually results in full on heat all the time , but if yours is leaking vacuum into the heater control valve's vacuum line , it would end up keeping the heater control valve closed , the reason for your no heat with the vacuum line in place .....

Randomtask2

iTrader: (1)

Wow. That was a lot of extemely important information, I was never taught any of that in school or in a shop or on my own. Damn I'm actually amazed that someone knew all this. Thank you so much. I couldn't imagine what else could be wrong. It's currently parked for the winter. But I will most definitely replace and reinstall this. Thank you so much. You have been a great deal of help.

OrangeBird

iTrader: (1)

I'm happy to help , I learned all this stuff by having to fix my own heat/AC and it got to the point where I had to borrow a friend's shop manual (the big one that costs over $100) to get mine all sorted . I just figure anyone I can help with the things I learned is money saved for all of us ( I know I sure ain't got $100 for a book describing how our heaters work ) .