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Old 10-07-2011, 03:28 PM   #1
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No hot air from heater ****FIXED****

Ok first I have done some forum searches and not able to find anything helpful on my situation. Here goes.

I am not getting any hot air from the heater when the control switch is in the hot position and the Heat or Defrost position.

Things I have checked:
I replaced the heater control valve under the hood. It looked like it might have been cracked.
I checked the temp of the in and out hoses from the heater core. They are both hot as the radiator hose after car has been running for awhile.
There is no hissing noise from the Control Unit.
Air does flow from defroster vents, forward vents and floor vents dependng on switch position.

I have read about a flapper door near the heater core that supposedly opens when heater is used. Is this door vacuum controlled or cable controlled? Also I am not sure how to access the door to see if it is working or not.

Any directions or pictures to help locate and test this door? I have a feeling this may be the culprit, since everything elsle seems to be right.

Also there is a vaccum line to the Heater Control Valve. What exactly does this vaccum line do and where does it come from? If it allows hot fluid into the Core which would make both in and out hoses hot, then it also seems to be working.

Any help would be greatly appreciated as the winter season is right around the corner.

Last edited by Cwaterboy1; 10-14-2011 at 06:52 PM. Reason: Problem solved
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Old 10-07-2011, 07:55 PM   #2
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Re: Not hot air from heater

I believe the hot/cold selector is cable operated on most F-bodies. Not in oddballs like the digi-dash GTAs, but most typical 3rd gens I believe it is.

Under the hood the heater control valve bypasses the heater core any time the hot/cold selector is in the full-cold position (some other qualifiers might apply like having it on max A/C setting). Never spent that much time worrying about it, but it is definitely tied in with the HVAC controls.
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Old 10-07-2011, 09:15 PM   #3
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Re: Not hot air from heater

First thing I would check is the hot/cold blend door. It's located under the dash on the passenger side, and it's easy to check if the door is moving. Just remove the under dash hush panel, and you will see the control lever. Just make sure that is moves when you move change the setting from hot to cold.
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Old 10-07-2011, 09:56 PM   #4
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Re: Not hot air from heater

the HVAC is vacum controlled
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Old 10-09-2011, 11:13 AM   #5
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Re: Not hot air from heater

On my old car I didn't have any heat from the heater and it was because the PO had removed the T-stat. Put a new T-stat in and had heat again.
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Old 10-14-2011, 02:12 PM   #6
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Re: Not hot air from heater

I think I am going to check the blend door movement while switching the temp control lever this evening.

I will report what I find.

Thanks.
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Old 10-14-2011, 06:50 PM   #7
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Re: No hot air from heater ***FIXED****

I checked the blend door and all seemed good. Pulled temp controller out and inspected all connections and no hissing noise. I put a vaccum guage on the line to the Heat Control Valve and there was a vacuum with temp control lever on cold. Only other thaing was the Heater Core. I discounted Control Valve and used a garden hose and forced water into the core from in and out side. The flow was restricted but finally some gunk and discolored water flowed out of the core and the flow was nolonger restricted.

I reconnected all the hoses and started her up and let her get hot and turned on the heater and WALA I had heat.

I want to thank all who passed on the advise and hope this helps others figure out any problems they may have with their heaters.
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Old 10-16-2011, 06:04 AM   #8
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Re: No hot air from heater ****FIXED****

Wow, that sounds like it was really crudded up! Glad to hear you got it fixed.

I guess the next obvious thing to do it a complete flush and fill on the cooling system- sounds like it's in desperate need.
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Old 01-22-2012, 09:52 AM   #9
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Re: No hot air from heater ****FIXED****

New issue.....Now with the colder days 20 to 45 degrees the engine will heat up to 200 degrees at idle and heat comes from the vents. Start driving and the engine temp drops to 120 degrees and cool air from the vents. It appears the fan is not running at this time but just cold air entering through the radiator. Could this cause the engine to cool down that far? I read somewhere some have to restrict air flow to allow for the engine to warm up more. I find it strange to have to do that with these already air flow restricted cars.
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Old 01-22-2012, 11:51 AM   #10
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Re: No hot air from heater ****FIXED****

Engine temp is regulated by the thermostat. Blocking airflow through the radiator is for big diesel school busses and dump trucks. Replace the thermostat first and see if it holds a more constant temp. Do the radiator cap while you're at it- there have been some real horror stories on here over the years from something as simple as a radiator cap. Plus, while you have it off you can make sure you actually have the cooling system filled up all the way!! (Seen that here many times, too)

Airflow through the HVAC system is drawn from the outside through a cowl opening at the back of the hood (under a screen to keep leaves and debris out), passenger side.

The electrical plug for the blower motor is easily accessible under the hood (round thing sticking out of the HVAC box). You can run a straight 12V jumper to it to test whether the motor itself is still working of if something else is causing the problem. Not totally uncommon for dash switches, resistor packs and various pieces of the blower motor's wiring harness to go bad from time to time. But test the motor itself first.
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Old 02-21-2012, 07:31 PM   #11
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Re: No hot air from heater ****FIXED****

I am going to give a new radiator cap a try....every thing else seems to be working ok. I did notice the overflow tank doesn't change levels wether it is cold or hot.
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Old 02-21-2012, 08:39 PM   #12
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Re: No hot air from heater ****FIXED****

[quote=Damon;5157838]Engine temp is regulated by the thermostat. Blocking airflow through the radiator is for big diesel school busses and dump trucks. Replace the thermostat first and see if it holds a more constant temp. Do the radiator cap while you're at it- there have been some real horror stories on here over the years from something as simple as a radiator cap. Plus, while you have it off you can make sure you actually have the cooling system filled up all the way!! (Seen that here many times, too)



If your heater core is still clear, put in a new thermostat and a new radiator cap.
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Old 02-21-2012, 09:11 PM   #13
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Re: No hot air from heater ****FIXED****

I have already put in a new thermostat, that was one of the first things I did when the car was overheating. I have changed out just about everything but the core and radiator cap. I changed the thermostat, temp sensor, temp switch, heater control valve, radiator and heater hoses. The car no longer overheats and the electric fan comes on at the right time, now it just won't stay hot during driving in cold weather. Setting idle the car will heat up likes it is suppose to but as soon as I start driving it starts to cool off fast. I have bled any air in the coolant system and it appears to be full of coolant.

So that is why I am at the radiator cap now. Crossing my fingers......
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Old 02-21-2012, 11:20 PM   #14
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Re: No hot air from heater ****FIXED****

If the car was still overheating after the new thermostat, it may have stuck in an open position. I'd put a new one in or if you don't want to spend the money, take your old one out and see what temperature it is (stamped on it) check it on the stove with a thermometer in a pot of water coming to boil to see at what temp it opens at.
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Old 02-22-2012, 10:43 AM   #15
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Re: No hot air from heater ****FIXED****

I have done all of this in my car and I still have no heat and it only blows wen it is on high.
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Old 02-22-2012, 12:54 PM   #16
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Re: No hot air from heater ****FIXED****

Quote:
Originally Posted by Sttn89 View Post
I have done all of this in my car and I still have no heat and it only blows wen it is on high.
When the car heats up during idle, do you get heat from the vents with the blower on high and then you lose the heat when you start driving? Or is it that your engine temperature warms up at idle but cools down when you drive and you never get heat in the car? .

This is a separate issue from the blower only working on high speed. Is this in a third-gen car or a full size car?
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Old 02-22-2012, 01:21 PM   #17
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Re: No hot air from heater ****FIXED****

The heat never comes on.Not at idle while im driving or anything.It is in a 89 caprice.It just blows cold air.
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Old 02-22-2012, 03:57 PM   #18
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Re: No hot air from heater ****FIXED****

Quote:
Originally Posted by Sttn89 View Post
The heat never comes on.Not at idle while im driving or anything.It is in a 89 caprice.It just blows cold air.
Have you checked the heater hoses. Is one of them hot/warm and the other cold? If so, your heater core may be plugged again. If its hot to the heater control valve, the valve may not be opening. If they are both hot, then it may be a flapper door or something internal. I'm not familiar enough with the big car setup to help any further.
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Old 02-22-2012, 04:06 PM   #19
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Re: No hot air from heater ****FIXED****

Quote:
Originally Posted by Sttn89 View Post
I have done all of this in my car and I still have no heat and it only blows wen it is on high.
Sorry, I thought that I was still addressing Cwaterboy1s problem. What have you done to try to fix the problem?


Cwaterboy1..has your problem been resolved?
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Old 02-24-2012, 08:51 AM   #20
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Re: No hot air from heater ****FIXED****

No......I put on a new radiator cap and it is still doing the same thing.


During idle for 10-15 minutes the temp guage does show around 220 and the radiator fan does come on. The heat blows hot in the car on any fan speed setting. Once I start driving the temp guage drops fast to 110-120 and the radiator fan is not running at this time. The air in the car starts turning cool fast. Then the temp runs steady at the 110-120 range. Mind you, this is when the outside air temp is close to freezing. When I stop driving and idle again the temp rises again to the 220 and my in-car air is hot again.

I did replace the thermostat but I would think that the temp would either stay hot (overheat) if it stays closed or stay cold if stays open. It never over heats.
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Old 02-24-2012, 08:59 AM   #21
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Re: No hot air from heater ****FIXED****

Could it be possible that the thermostat opens during idle at the right time (195) to keep from overheating and then when I drive the pressure builds up and does not allow the thermostat to close once it had open during idle. Then when I return to idle the thrmostat is allowed to close which builds the temp back up?
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Old 02-24-2012, 11:17 AM   #22
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Re: No hot air from heater ****FIXED****

I don't think I've ever heard of that happening but the problem still sounds like the thermostat. They're cheap enough that I'd probably try a different brand of thermostat in case that or something like that is happening.
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Old 02-26-2012, 06:58 PM   #23
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Re: No hot air from heater ****FIXED****

Ok think I figured it out. Back when the car was overheating, I hade changed the thermostat. I bought the most exspensive one thinking the best should cost more. Well, I think the car had come close to overheating again when I found the Fan wasn't coming on when it was suppose to. I got that fixed which was during the summer time and the car ran cooler. Now it is winter time and the car wouldn't warm up while driving. So tried the radiator cap and still no warming. So I figured maybe I got a bad thermostat and went to replace it again. Guess what I found, I had bought a FAILSAFE thermostat and didn't realize what it was suppose to do. And back when it closely overheated the mechanism worked which holds the thermostat open all the time until reset or replaced.

So all this time the thermostat has been stuck open. Reset it and re-install and now getting ready to test it out.
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Old 02-26-2012, 07:16 PM   #24
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Re: No hot air from heater ****FIXED****

Most pros don't install those fail safes, reason is when your trying to get all the air out of the cooling system, sometimes the temp will spike (b/c of trapped air) causing the fail safe to open.
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Old 02-26-2012, 07:26 PM   #25
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Re: No hot air from heater ****FIXED****

Quote:
Originally Posted by Cwaterboy1 View Post
Ok think I figured it out. Back when the car was overheating, I hade changed the thermostat. I bought the most exspensive one thinking the best should cost more. Well, I think the car had come close to overheating again when I found the Fan wasn't coming on when it was suppose to. I got that fixed which was during the summer time and the car ran cooler. Now it is winter time and the car wouldn't warm up while driving. So tried the radiator cap and still no warming. So I figured maybe I got a bad thermostat and went to replace it again. Guess what I found, I had bought a FAILSAFE thermostat and didn't realize what it was suppose to do. And back when it closely overheated the mechanism worked which holds the thermostat open all the time until reset or replaced.

So all this time the thermostat has been stuck open. Reset it and re-install and now getting ready to test it out.
Let us know how it works out.
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Old 02-26-2012, 08:05 PM   #26
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Re: No hot air from heater ****FIXED****

After bleeding the air and topping off the coolant in the raidiator while the car is running with thermostat open and filling the coolant resevoir to the Full Hot line and then capping the radiator, the temp seems to bounce from 195 to 220 while idle and driving. The hot air does cool a little and then get hotter during the temp fluctuation. But the temp no longer drops to 120 or so and the air no longer turns cold.

It seems acceptable for now until the heater core gives now theat that the system is full and pressurized.....crossing fingers that it won't.
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Old 02-26-2012, 08:32 PM   #27
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Re: No hot air from heater ****FIXED****

Ive never heard of a fail safe thermostat, Ill have to check those out.
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Old 02-26-2012, 08:46 PM   #28
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Re: No hot air from heater ****FIXED****

I didn't realize exactly how they worked when I installed it, I just knew I paid more for it than a regular thermostat and I was having probelms with overheating. I figured it out when I pulled it out and it was held in the open position by some clips on the housing. It appears when the temp reaches a very high level the thermostat opens to a point that these clips engage the moving outer ring of the thermostat and does not allow for it to close. You have to remove it and dis-engage the ring or replace it for it to operate correctly again.

Lesson learned......
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Old 02-26-2012, 09:40 PM   #29
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Re: No hot air from heater ****FIXED****

Sounded like the thermostat. Glad you got it working!
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