96 Tahoe Heater Only Blows Warm Air

[Laredo1307]

Hey guys, I'm a bit stumped on this one.

My heater is currently only blowing warm air out of the vents.

I do not appear to have any coolant leaks that I can see inside or outside for starters. My radiator, upper & lower hoses, temp sensor, and thermostat were all replaced in September. The cooling system on the truck has been operating perfectly fine.

Things I've recently performed

- Just replaced the blower motor resistor after the old one was failing
- Just installed a new ac control module because the old knobs were failing
- Both the inlet and return line for the heater core feel very hot outside my firewall so I assume the heater core is functioning properly. there's no leaks that I can determine
- I recently replaced the vacuum line to the heater control valve solenoid after it cracked. I assume the heater control valve is working if the heater core lines are both very hot?
- I pulled the glove box and I can see the blend door actuator turning when I switch from cool to heat. The air goes from cold to warm. my other two actuators appear to be functioning properly as well.

Not sure what else to check at this point.

Could my blend door actuator not be working properly if it wasn't in the correct position when I installed the new AC control module?

 

[Laredo1307]

FYI, I decided to unplug the heater control valve vacuum tube that goes to the solenoid and my heater immediately started blowing hot air. Previously I had only tried unplugging the vacuum line from the engine to the Solenoid and it made no difference.

I tested the voltage going to the solenoid and it was 12V when the cold air is on and 0V when the hot air is selected. I assume that’s working properly so I must have a bad solenoid.

Will update after I replace with new.

 

[Laredo1307]

Update:

No parts replaced. What I discovered was that my heater core was dry locked. I had replaced my radiator over the summer and of didn’t turn on my heater when I went to replace fill new antifreeze.

Just had to squeeze the heater core hoses a few times with the truck warmed up and the heat all the way on. Then added back the missing anti freeze.

 

[GoToGuy]

Define what is " dry locked " ? How does a pressurized water system get this ? What did squeezing the heater hose do. If the solenoid valve is open heated coolant flows. If it's closed the water just sits, not moving.

 

[Laredo1307]

I can only assume there was a pocket of air trapped in the heater core after I replaced the radiator and hoses over the summer. My guess is that there wasn’t enough pressure in the current system to overcome the trapped air whenever I turned on the heater finally and the valve opened.

I basically just squeezed the hoses multiple times going into the heater control valve and then the ones going into the firewall. That seemed to burp the air out of the heater core which left me adding about 1/2 a gallon of antifreeze.

Air coming out of the vent went from 110F to 140F

 

[L31MaxExpress]

That is why I have started vacuum filling everything now and then use a Lisle bleeder funnel when I am done to ensure all the air is sucked and forced out.

 

[GoToGuy]

Did you pressure flush the heater core, that's a common cause of low heat from heater. Most likely heater valve was closed. When you did the flush and fill you should have had the heat on hot, and fan on . As the service manual references. the coolant is moved pumped under pressure by the water pump , as it heats and cools it will self bleed any residual air through coolant recovery cap.

 

[1madmouse]

That is why I have started vacuum filling everything now and then use a Lisle bleeder funnel when I am done to ensure all the air is sucked and forced out.

I have used these funnels and had amazing luck on vehicles that would not bleed otherwise.

 

[L31MaxExpress]

I have used these funnels and had amazing luck on vehicles that would not bleed otherwise.

I have started using those funnels bleeding everything. The adapters seal to many types of radiator caps and that nice little plug with the T-handle lets you remove it without making a huge mess. I have even gotten to where I use the vacuum filler and the funnel on vehicles that do not even really need it like my van because it makes less of a mess and prevents that startup air pocket from ever being a problem. Even after vacuum filling it, because of the mile long heater hoses, rear heater core and stuff like that the van bubbled away for a solid 30 minutes of running.

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[1madmouse]

I absolutely use for every vehicle
I have seen as you have that it takes a bit for all the air to get out. Some have no heater until all the air is bled. Love the no-spill and plenty of adapters for a good seal.