DiyMobileAudio.com Car Stereo Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
599 Posts
Discussion Starter #1
This is a problem I've had w/ this car for several years. I've done all the basics -- I've made sure the coolant level is full, there's no air in the coolant, the thermostat is working, and the temp gauge is in the proper range. I've also felt the radiator and heater hoses and all of them are warm/hot and they all have about the same temp. I even replaced the heater core becuz it was leaking, and that didn't fix the lack of heat. I've also reset the blend door actuator by using a procedure that involves pulling the HVAC fuse. Finally, I tried replacing the actuator. None of this has fixed the problem.

Sometimes the heat in the car is reasonably warm, usually it's chilly, and sometimes there doesn't seem to be any heat at all. During the 1st 20 miles of my commute this morning, I could still see my breath in the car. Then it finally warmed up a bit for the last 10 miles of my commute. The outside temp was about 30°F, so it wasn't even that cold out.

The only other thing I can think to do is pull the heater box apart and inspect the blend door itself to see if it's sticking or damaged. But it's a PITA to get to, and it doesn't seem likely that it's damaged. Any other thoughts or relevant experience?
 

·
Registered
Joined
·
599 Posts
Discussion Starter #3
Have you noticed the electric fan running continuously ?
U'r thinking the fans under the hood are running and keeping the engine colder than it should be? It's a good thought, but I don't think that's the problem...

I left the car running after I got home from a long drive as I checked how warm the radiator and heater hoses are, and the fans weren't running then. And the temp gauge indicates that the engine comes up to normal operating temperature within a reasonable time after a cold start and maintains that temp as a I drive.
 

·
Registered
Joined
·
713 Posts
Ok, next is to check the temperature of the heater core housing, or heater plenum where you can reach it and get your hands on it.
If it seems good and warm/hot then a plenum door is probably stuck.
Rotten job to repair......

I have the same issue in my suburban from time to time, it will happen after a big bass song, the sub actually makes the main directional blend door jump out of its socket !
And of course, it's a pita to access.
 

·
Premium Member
Joined
·
3,486 Posts
Ok, next is to check the temperature of the heater core housing, or heater plenum where you can reach it and get your hands on it.
If it seems good and warm/hot then a plenum door is probably stuck.
Rotten job to repair......

I have the same issue in my suburban from time to time, it will happen after a big bass song, the sub actually makes the main directional blend door jump out of its socket !
And of course, it's a pita to access.
Those $20 IR heat guns are handy for putting numbers to these things...
 

·
Registered
Joined
·
599 Posts
Discussion Starter #6
Ok, next is to check the temperature of the heater core housing, or heater plenum where you can reach it and get your hands on it.
If it seems good and warm/hot then a plenum door is probably stuck.
Rotten job to repair......

I have the same issue in my suburban from time to time, it will happen after a big bass song, the sub actually makes the main directional blend door jump out of its socket !
And of course, it's a pita to access.
My dad has an IR gun, so hopefully I can get a line-of-sight to the heater core to check its temp. Still, if the hose going in and the hose going out are both hot, it stands to reason the core must be hot too.

The blend door seems more likely, but my bass isn't really that loud. But I suppose if it hits the right resonance, it still could shake something loose. On the other hand, I don't have any problems w/ the temp in the summer -- the AC gets good and cold. If the blend door was sticking, it seems like warm air from the core would get mixed it.
 

·
Registered
Joined
·
713 Posts
Obvious question but I'll ask :
How is the air flow , and does the air flow change when going from vent to floor or defrost ?

The car is old enough now that the plastics are losing their flexibility, things get stuck.
Also, depending on the model, there should be three or even four blend doors in that
system.
Over complicated and prone to these issues when aging.
If you google " ( model of car ) HVAC system " the diagrams are straightforward enough.

I have found all sorts of things in heater / ac systems, including rats, mice , screwdrivers, nuts& bolts, pencils.... ( you get the idea ....). Hint hint.
 

·
Premium Member
Joined
·
3,486 Posts
My dad has an IR gun, so hopefully I can get a line-of-sight to the heater core to check its temp. Still, if the hose going in and the hose going out are both hot, it stands to reason the core must be hot too.

... On the other hand, I don't have any problems w/ the temp in the summer -- the AC gets good and cold. If the blend door was sticking, it seems like warm air from the core would get mixed it.
Well this points to the air flow not being able problem.
It is either water flow or water temp, and the thermostat controls the minimal engine temp and warm up.
The electrics fans in the front willl not chill the water.

It is more likely a stuck closed valve or obstruction of some sort.

Maybe it is possible to (back)flush out the core from the hose side? Which would test if the core itself was flowing.
 

·
Registered
Joined
·
220 Posts
My Brother had a Ford Ranger that had heat problems... it was a valve on the hoses that go into the heater core. The valve was bad and would not allow the hot coolant to enter the heater core. I don't know if your car has something similar but I do know that Pontiac like to add a bunch of crap to their cars.
 

·
Registered
Joined
·
599 Posts
Discussion Starter #12
Obvious question but I'll ask :
How is the air flow , and does the air flow change when going from vent to floor or defrost ?

The car is old enough now that the plastics are losing their flexibility, things get stuck.
Also, depending on the model, there should be three or even four blend doors in that
system.
Over complicated and prone to these issues when aging.
If you google " ( model of car ) HVAC system " the diagrams are straightforward enough.

I have found all sorts of things in heater / ac systems, including rats, mice , screwdrivers, nuts& bolts, pencils.... ( you get the idea ....). Hint hint.
Airflow is good, whether it's coming out by my feet, the vents, or the defroster. There are 3 doors in this system -- the mode door (which controls where the air comes out), the blend door (temp) and the recirculation door (mixing in fresh air or recirculating air from the interior of the car). It's definitely not the mode door. And I don't think it's the recirc door becuz I use that a lot during the summer and it seems to work fine. So the most likely explanation is that the blend door is either damaged or obstructed. I tried searching for an exploded view of the heater box/duct work in the car so I would know exactly where to access the blend door, but I couldn't find anything. Still, I know where the blend door actuator goes, so I'll start in that area.

It is either water flow or water temp, and the thermostat controls the minimal engine temp and warm up.
The electrics fans in the front willl not chill the water.

It is more likely a stuck closed valve or obstruction of some sort.

Maybe it is possible to (back)flush out the core from the hose side? Which would test if the core itself was flowing.
There aren't any valves on the heater hoses, and as I've mentioned, I replaced the heater core becuz the old unit was leaking and that didn't affect the poor heat problem.

I used the IR thermometer yesterday when I got home after a long drive, w/ the engine running and an outside air temp of about 45°F:

Top radiator hose: 199°F
Bottom radiator hose: 180°F
Heater core inlet hose: 185°F
Heater core outlet hose: 135°F
Air vent in car, set to full hot: 88°F

Based on my research, the air vent should be about 140°F-160°F at full hot. All the other numbers look correct, although the fact that there's a 50° differential on the heater core shows that heat is being removed. So the low temp from the air vent indicates that cold air must be getting mixed in w/ the hot air blowing thru the core. This again points to the blend door not closing properly.

Surely you've seen this ....

Yep... I'm pretty sure that's the video I watched before I replaced the blend door actuator.

On the other hand, I don't have any problems w/ the temp in the summer -- the AC gets good and cold. If the blend door was sticking, it seems like warm air from the core would get mixed it.
I thought about this some more, and when using AC, the blend door would seal off the heater core from the rest of the airflow. But when it's on full heat, the blend door would direct all airflow thru the heater core. If the blend door is obstructed, it may be able to seal on 1 side but not the other, and that would explain why I have good cold air but poor heat.
 

·
Premium Member
Joined
·
3,486 Posts
...

There aren't any valves on the heater hoses, and as I've mentioned, I replaced the heater core becuz the old unit was leaking and that didn't affect the poor heat problem.
...
Unless it is the only car without a value that is attached the red-blue heat knob... then there is likely a value somewhere???
(i.e. B.S.)
 

·
Registered
Joined
·
220 Posts
Unless it is the only car without a value that is attached the red-blue heat knob... then there is likely a value somewhere???
(i.e. B.S.)
Sometimes there is a valve at the thermostat, sometimes in the dash like the video, sometimes on the hoses going to the heater core, Sometimes it is a junction under the intake manifold... it is there somewhere.

Meaning I agree with you.
 

·
Registered
Joined
·
713 Posts
Unless it is the only car without a value that is attached the red-blue heat knob... then there is likely a value somewhere???
(i.e. B.S.)
No, not with this design ( if you are talking about a liquid valve ), Chevy of this era has the hot hose direct to the heater core from the intake manifold, from there it goes straight back to the top of the radiator.

The only control for heat / cold is a few blend doors, the heater core is always charged.
when the heater core blend door is closed there is no air flow through the plenum.
these doors get sticky all the time, and the electronic module that controls them cannot overcome the force needed to fully open or close them.
( or the gear set in the modules crack, also common, but this problem has been addressed by replacement. )
 

·
Listener of Music
Joined
·
2,919 Posts
I had this problem with a 95' Silverado. It constantly ran cold. Never really had hot air out the heater. It was warm enough but not as it was supposed to be. I changed everything. GM changed everything. Never figured it out. The dealer said let it warm up longer in the winter! Not in a bad way. They were more helpful than I could imagine. But really know one ever figured out why. Had the truck for 5 or 6 years and it never got hot.
 

·
Registered
Joined
·
713 Posts
I had this problem with a 95' Silverado. It constantly ran cold. Never really had hot air out the heater. It was warm enough but not as it was supposed to be. I changed everything. GM changed everything. Never figured it out. The dealer said let it warm up longer in the winter! Not in a bad way. They were more helpful than I could imagine. But really know one ever figured out why. Had the truck for 5 or 6 years and it never got hot.
Was the silicon clutch on the rad fan checked ?
 

·
Registered
Joined
·
713 Posts
I honestly don't remember. I just know in the winter I let it warm up longer!
I'm putting serious thought into ditching the coolant fan assembly on mine and going electric this winter.
The radiator in there is the long four core and come -20c she never warms up either.
 
1 - 20 of 27 Posts
Top