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Heater blowing luke warm at best

R

Rodd

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Antelope, CA
I was out tonight and couldn't get my heater or defroster to blow warmer than luke warm. Cold works just fine. It is only 47 degrees out. The rear air blows hot w/ no probs. Where do I look first?
 
Does it blow lots of volume, but only warm? If so you need to flush your heater core.
If it does not blow very good, you may have a diverter flap stuck half way between hot and cold, or the heater core or ac coil are gunked up.
 
I had a heat issue too. It turned out to be the pressure switch for the AC. While in the defrost mode the AC compressor would stay on, freezing up the coil resrticting the air flow. Had the same issue in summer and winter. I replaced the switch and problem solved.
 
If it is the heater core why is the rear working and the front not? Where is the heater core? Isn't it connected to the cooling system (coolant)?
 
mfgguru said:
Does it blow lots of volume, but only warm? If so you need to flush your heater core.
If it does not blow very good, you may have a diverter flap stuck half way between hot and cold, or the heater core or ac coil are gunked up.
Click to expand...

Yes, the volume is there just not much heat.
 
Rodd said:
If it is the heater core why is the rear working and the front not? Where is the heater core? Isn't it connected to the cooling system (coolant)?
Click to expand...

The heater core is just inside of the cab, and the ends stick through the firewall for the heater lines to attach to. It is on the pass side near the ac condenser. Follow the line that attaches to the t-stat crossover and it runs to the heater core. IIRC, on the suburbans, the line has a T in it that runs to the rear heater.
 
Last edited:
AlbertaRedneck said:
The heater core is just inside of the cab, and the ends stick through the firewall for the heater lines to attach to. It is on the pass side near the ac condenser. Follow the line that attaches to the t-stat crossover and it runs to the heater core. IIRC, on the suburbans, the line has a T in it that runs to the rear heater.
Click to expand...

Thanks! I'll check it out. If it has a "T" is it valved? It could be the valve/flap that was mentioned earlier mfgguru.
 
Rodd said:
If it is the heater core why is the rear working and the front not? Where is the heater core? Isn't it connected to the cooling system (coolant)?
Click to expand...

You have 2 heater cores... the hot coolant comes from the engine, through a T-valve to separate it into front and back, and the hot coolant flows to both heater cores. If the heat controls are 'on', then the hot coolant flows THROUGH each respective core, then back to the engine.

At each point, you have a diverter that decides whether the hot coolant goes through the core or not (possible problem spot) controlled by a thermostatic switch (possible problem spot) and each core itself is a possible problem spot. Also, air has to go through the core, and that's controlled by a flapper, so air volume is also a possible problem spot.

As Jody mentioned, the switched AC valve is also a possible issue.

Trace the flow, look at each spot, and isolate your issue. If the hose going IN to a core is hot, and the hose coming OUT isn't, the core is a problem. If the line is hot on one side of a valve and not on the other, the valve (or the controller) is a problem. If you don't have enough airflow, the flapper (or servo) is a problem.

The fact that your rear heat is fine tells us your thermostat and waterpump are OK, and that you don't need a rad cover, so you're half-way there...
 
I was just about to post about the opposite problem - my front heat is OK, it's my rear heat that doesn't warm up. Thanks, Rodd - you saved me some typing!
 
JiFaire said:
You have 2 heater cores... the hot coolant comes from the engine, through a T-valve to separate it into front and back, and the hot coolant flows to both heater cores. If the heat controls are 'on', then the hot coolant flows THROUGH each respective core, then back to the engine.

At each point, you have a diverter that decides whether the hot coolant goes through the core or not (possible problem spot) controlled by a thermostatic switch (possible problem spot) and each core itself is a possible problem spot. Also, air has to go through the core, and that's controlled by a flapper, so air volume is also a possible problem spot.

As Jody mentioned, the switched AC valve is also a possible issue.

Trace the flow, look at each spot, and isolate your issue. If the hose going IN to a core is hot, and the hose coming OUT isn't, the core is a problem. If the line is hot on one side of a valve and not on the other, the valve (or the controller) is a problem. If you don't have enough airflow, the flapper (or servo) is a problem.

The fact that your rear heat is fine tells us your thermostat and waterpump are OK, and that you don't need a rad cover, so you're half-way there...
Click to expand...

Thanks Jifaire! You have given me the whole pie not just a piece. I just have one other question. Do I need to take apart my dash or part of it to get access to the heater core?
 
Not sure, but possibly... you can see the hoses at the firewall... start there.

You can probably inclip things from the bottom to get at stuff, but you may need to pull your glove compartment to see everything.

I've never taken a GM truck core apart... I just know how they are supposed to work.
 
I don't know if this is related but my wife was driving and the ses light came on. It was p0126 coolant temperature too cold for normal operation. It was 131 degrees at 35 mph and 2% load. My wife said that it happened within 5 minutes after starting the truck to come home after sitting for 4 hours. The temp outside was 45 degrees.

I cleared the code drove 30 miles and no probs. The front heat is blowing warm now. Not hot like normal. Could this all be related?
 
tell ya what... cut up a beer box, use it and some nylon zip ties to cover up your grille and restrict the airflow into the rad.

If the problem goes away, you know that your thermostats are sticking, and you have a choice... you can fix them, or keep drinking beer so you can replace the box when it gets wet and ratty-looking.

I know what I would choose :D
 
JiFaire,

I don't even have a problem with my heater but I've chosen to follow your advise and cut up a beer box and drink some beer. Is this like preventative medicine?

Rodd,

It's like every problem you have should be made a sticky. Plus, you don't have "no" in your heart. I'm curious if you can turn empty beer cans into an exhaust pipe but I'll wait and see.
 
JiFaire said:
tell ya what... cut up a beer box, use it and some nylon zip ties to cover up your grille and restrict the airflow into the rad.

If the problem goes away, you know that your thermostats are sticking, and you have a choice... you can fix them, or keep drinking beer so you can replace the box when it gets wet and ratty-looking.

I know what I would choose :D
Click to expand...

If I drank that would be an option. If I can't get it figured out then I just might start. :eek: I will replace the thermistats in hopes that, that is the problem. That would be easy.
 
Dan Hunter said:
JiFaire,

I don't even have a problem with my heater but I've chosen to follow your advise and cut up a beer box and drink some beer. Is this like preventative medicine?
Click to expand...

Hey Dan... it's Dr. Faire...
Take 2 MGD and call me in the morning :)

Your heater may still blow cold, but you won't feel it. If the feeling starts to return, repeat the prescription as required.

Us Canucks know how to deal with cold :D
 
JiFaire said:
Hey Dan... it's Dr. Faire...
Take 2 MGD and call me in the morning :)

Your heater may still blow cold, but you won't feel it. If the feeling starts to return, repeat the prescription as required.

Us Canucks know how to deal with cold :D
Click to expand...

Jim, shouldn't you have also said "repeat as necessary"? :smile5: Leo
 
I went to Autozone to pick up a couple of Tstats and they had some in stock for $13 and some that were oem style for $35 a piece. The guy said the oem style are higher flow than the cheap ones. Anyone have any thoughts as to which ones to use?
 
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