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Discussion Starter #1
Apologizing in advance if this is wordy,

For those of us who live in Colorado you know it's been warm in the Denver area the last few days and then today it dropped and started snowing a bit, when I went to turn my temp knob from the cool setting to full heat setting I was disappointed to find out that my heater was blowing cold air after the car had fully warmed up. Just a few days ago before it got warm my heater blew hot air just fine, it has been good since I bought the car in august. Here's what I have tried thus far and have still failed to correct the problem:

Checked that the control arm from the temp dial was connected to the heater control valve, it is and everything moves freely

Coolant level is good, changed coolant and thermostat 5 months ago

Car warms up to operating temp as it should normally

Reaching through speaker hole in dash I can feel both the lines after the valve are hot to the touch, what I can touch of the actual heater core is also hot, too hot to touch for very long once car is at operating temp.

Thinking maybe the heater core was clogged I pulled the hoses to the core off and flushed it with a garden hose, I sprayed through both holes and there didn't appear to be any restriction

After that I refilled the system and bled it for about 30 minutes till no more bubbles appeared at the bleed screw or in the reservoir and still no hot air through any of the vents. I have not touched anything on the car in the last few days since it worked, the only abnormal thing it went through was being set on cold for a few days with the nice weather which it hasn't been left on this setting for an extended period of time since summer.

Again sorry if this is wordy I just wanted to cover everything I can think of.
If it helps it's an 87' 900 turbo 16v with 250,000 miles on it.

Any suggestions on what I should try next?
Thanks for the help!
 

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Discussion Starter #2 (Edited)
Also occurred to me to ask this, is there any chance of an air bubble getting trapped somewhere in or near the heater core that could cause this? I massaged the hoses to try and work out any bubbles and drove it around then bled it again but still no luck.
EDIT I can deffinately tell there is an air bubble in the upper hose going from the water pump to the heatercore but I can't get it out. Does anyone know how to do this? I get heat temporarily if I massage the hoses to push coolant into the core so I'm fairly certain the air bubble is to blame I just can't get rid of it.
 

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Ignore that entire post by me about heater valves

I just read your post properly.

The center vents will ALWAYS blow cold air, the side vents, floor vents, and windsheild vents will blow hot air. Change your air diffuser to up or down arrow or both, or <> and turn off the center vents by pushing the slide closed on the vent itself.

If your air diffuser/selector switch doesn't hiss when you change it from a setting to say the 0 setting then you may have a cracked vacuum line and lost vacuum control of your vents. Now if this is the case you will not have any vents open but the center vents (which blow fresh outside air 24/7), regardless of where the selector switch is set to.

If you are not getting air flow from fan from any other vent except center vents regardless of selector switch position then suspect this problem, the vacuum hose normally breaks in the engine bay where it is connected from the vacuum canister in the right wheelwell and goes just below the air conditioner evaporator housing (right side in firewall)
 

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Discussion Starter #4
What type of heater valve do you have? is it black or white/orange?

Can you actually see the heater control arm move through the speaker grille (speaker grille removed) when you turn it, can you see the gears on the heater control valve turning?

I'm willing to bet it's the control to the heater valve in some way shape or form. Look harder.

No air bubbles will not stop your coolant from flowing into the heater core. I highly doubt the fluid side of things is your problem. If the heater hoses going to the core are warm but you have no heat in the cabin then it's a control arm issue.
I have a black valve and I can see that the valve itself (not just the armature coming from the knob) is moving. I know it's not stuck closed because I could run water in one hose to the core and it came out the other hose with no drop in flow, just to check I closed the valve and could not get water to pass through. I can get heat for a couple seconds if I squeeze the upper hose to force coolant into the core but I can't keep it flowing once I stop massaging the hose.
 

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It still may be the valve. You may need to take it out and have a look. I wonder if the gears are worn out and the valve is actually closed. Its not a tough job after the knee bolster comes off. 2 bolts in the corners of the bulster. And 1being the ash tray.
 

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Discussion Starter #6
It still may be the valve. You may need to take it out and have a look. I wonder if the gears are worn out and the valve is actually closed. Its not a tough job after the knee bolster comes off. 2 bolts in the corners of the bulster. And 1being the ash tray.
Guess I'll try that. If I replace it how do I get the air bubble in that hose out afterwards?

Thanks for everyone's input by the way I was running out of ideas.
 

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NO READ MY AMENDED POST ABOVE!

I didn't read your post properly. I missed what you said about water running through it...

Don't go pulling anything apart yet - Please just read my amended post and report back what you've found!

If you don't get air out of any vents regardless of position of selector then you have a vacuum leak for vent controls. center vents always blow cold air !!! ^^^^^^^
 

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Discussion Starter #8
NO READ MY AMENDED POST ABOVE!

I didn't read your post properly. I missed what you said about water running through it...

Don't go pulling anything apart yet - Please just read my amended post and report back what you've found!

If you don't get air out of any vents regardless of position of selector then you have a vacuum leak for vent controls. center vents always blow cold air !!! ^^^^^^^
Verified that I have vacuum going to the distr knob. Everything there works properly and the vent doors open and close when they should.
 

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so you have cold air blowing out side vents or windshield etc, but when you turn it you don't have hot air?

Wow I was almost sure that was the culprit :p

If the heater core is hot then there is no reason why you shouldn't have hot air..?
 

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Discussion Starter #10
so you have cold air blowing out side vents or windshield etc, but when you turn it you don't have hot air?

Wow I was almost sure that was the culprit :p

If the heater core is hot then there is no reason why you shouldn't have hot air..?
Yes I have cold air coming out of all vents all the time. I can feel that the lower hose (both before and after the heater core valve all the way to the actual heater core) is hotter than the top hose which is why I feel the air bubble has something to do with this. As I said above if I squeeze the upper hose repeatedly in a way that moves coolant into the core I get hot air coming out of all the vents (depending on which position the distr knob is at) for about 10 seconds until the coolant in the core cools off some.


I'm 99.999% sure that this air bubble in the upper hose is the cause I just can't get it out no matter what I try.
 

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I'm almost certain an air bubble can't do that, your problem lies in your heater control valve, it's seized or simply closed.

Seeing as we're talking in percentages :p I'm 99% sure when the valve is closed it doesn't stop water flowing through it, if you point a hose in 1 tube water is going to come out of the other one because it allows the water to keep circulating despite the valve being closed. Otherwise that would be counter productive for coolant flow around the engine every time the heater was switched off. You need to actually visualise the gears of the black heater control valve moving when you turn the heater control, if they/the heater control rod isn't turning properly there is your problem.

Another way you can test to see if your heater control valve is open (which I am sure it isn't) is to remove both top and bottom heater hose, and blow through either one of the pipes coming out of the firewall (be careful ethylene glycol is poisonous) you can use your hand over the pipe to protect yourself. Blow into the tube, it will gurgle (deep gurgling sound) if the valve is open to the heatercore. If it is closed it will simply spit water at you out the other pipe, you will feel very little resistance because the path of flow through the tubes when the valve is closed is very short.

I've done this myself and know 100% it works.
 

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Discussion Starter #12
I'm almost certain an air bubble can't do that, your problem lies in your heater control valve, it's seized or simply closed.

Seeing as we're talking in percentages :p I'm 99% sure when the valve is closed it doesn't stop water flowing through it, if you point a hose in 1 tube water is going to come out of the other one because it allows the water to keep circulating despite the valve being closed. Otherwise that would be counter productive for coolant flow around the engine every time the heater was switched off. You need to actually visualise the gears of the black heater control valve moving when you turn the heater control, if they/the heater control rod isn't turning properly there is your problem.

Another way you can test to see if your heater control valve is open (which I am sure it isn't) is to remove both top and bottom heater hose, and blow through either one of the pipes coming out of the firewall (be careful ethylene glycol is poisonous) you can use your hand over the pipe to protect yourself. Blow into the tube, it will gurgle (deep gurgling sound) if the valve is open to the heatercore. If it is closed it will simply spit water at you out the other pipe, you will feel very little resistance because the path of flow through the tubes when the valve is closed is very short.

I've done this myself and know 100% it works.
I can see the gear attached to the armature move but will have to wait till tomorrow to get knee bolster off and have a proper look. Will try the blowing test too, when I first flushed it out with the hose it took about 10 seconds to turn from green to clear which makes me feel like it was pushing the coolant out of the core and not just bypassing it. If it were bypassing I feel the water would have turned clear much quicker but I could be wrong. Not the first time :p

I'll report back tomorrow with the results thanks for your insight I didn't realize there was a bypass in that valve.

Of course I'll have my heat fixed just in time for more warm weather :D
 

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so you have cold air blowing out side vents or windshield etc, but when you turn it you don't have hot air?

Wow I was almost sure that was the culprit :p

If the heater core is hot then there is no reason why you shouldn't have hot air..?
It had to be the valve. If the arm is connected
 

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The other thing is that I'm not familiar with,

Some 900s were equipped with bypass valves (not the heater control valve) these valves were to direct fluid from engine circulation directly to the heater core for super fast warm air in snowy conditions etc.

I am not familiar with these as they never came in Australia as far as I am aware (NO snow :D) these occasionally do fail and cause no heat problems.

Google - heater bypass valve - no heat saabcentral or similar to look for threads.

If it took that long it sounds like you were flushing coolant out of the heater core. A truly strange scenario if your heater core is open and you don't get hot air. That bypass valve thing is the only other thing I can think of causing your problem.

Does your temp gauge show a reading once engine has warmed up>? as in, someone hasn't removed the thermostat have they?

Just random ideas. Man I'll be interested to know what fixes it :cheesy:
 

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Discussion Starter #15
Yeah I checke for the bypass valve (looks like a weird piece of hose) and I do not have them. I believe they came on 90' and later models?

As for temp I have a thermostat in there that I installed 5 months ago. All the hoses except for the one going from the waster pump to the top port on the firewall are too hot to touch very long and aforementioned heater core hose is kind of hot and gets as hot as the rest temporarily if I squeeze it repeatedly. This is what has me convinced that the air bubble is the issue.

But I still plan on pulling the knee bolster to get a better look at the valve when I'm off work later today. I'll let you guys know what I find.
 

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I have never had to bleed the heater core to clear air. There is enough pressure from the water pump to do this for you automatically. I think the most likely cause is the heater valve is not opening properly for some reason, either actuation or broken internals.
 

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hey i just had this issue and was able to fix it. i took the speaker cover off on the left side, reached my hand down to the valve and used my pinky to push the slider down just a hair and i have heat again, im willing to bet its that.
 

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Discussion Starter #18
hey i just had this issue and was able to fix it. i took the speaker cover off on the left side, reached my hand down to the valve and used my pinky to push the slider down just a hair and i have heat again, im willing to bet its that.
The slider that the gear moves? I'll try that. As for the valve it looks good on the out side I can feel both gears moving as I turn the knob.
 

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Discussion Starter #19
The slider that the gear moves? I'll try that. As for the valve it looks good on the out side I can feel both gears moving as I turn the knob.

Tried that to no avail. I'm assuming the internals of the valve are damaged and the inadequate flow is causing the air bubble to stay trapped.
Time to track down a new valve...
 

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Discussion Starter #20
Update: got a new valve but can't get all four screws to thread in properly is there some special trick I'm missing?

Also I took the old valve apart and there were no obvious signs of damage, the valve opened as it should and closed as it should. Nevertheless I will finish installing the new valve tomorrow and hope it works.

Thanks!
 
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