Help me diagnose heater blowing Luke warm.

[someotherguy]

Since you've already pulled the lower cover (heater core access) you've crossed that bear; you can pull the heater core too and see if the temperature control door is working properly. I honestly have never seen one go bad.. I've seen a *few* of the temperature control actuators go bad. Just a few.

You mentioned weak airflow earlier.. that's why I brought up evap blockage with debris. It's super common as there's no filtration of incoming air to the system on these trucks.

Richard

 

[98chevy2500SS]

OP, have you checked what your coolant level is? When I had my 97, the heat was luke warm at best. After the engine cooled down, I checked the coolant and it was pretty low. Filled it up to the brim, waited until the bubbles quit, then it finally blew hot air. May or may not fix your problem, but it's worth a check.

 

[Jayboney]

Okay, so pulled the heater core down far enough to check temp door above and its definitely operating like it should. I'm kind of at a loss, a/c and fresh air blowing good turn to heat and it kinda warms up but not hot. Should I flush system? I replace the heater core about 3 years ago and I didn't really have a problem till the end of last winter.

 

[Jayboney]

98Chevy2500ss-
Yes it's one of the first things I did, coolant level is full and both hoses hot going to heater core.

 

[east302]

Take a look at the actuator and see if it’s rotating completely. There’s a silver position indicator dial with a notch in it (colored blue in photo below). There are small marks at 11 and 1 o’clock.

From full hot to full cold, the notch should align from one to the other.

If it is hanging, then I’d replace it. Just did mine on a 98 a few months ago, I could hear it grinding when I got up close to it. Some of the internal plastic gears were cracked.

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[Jayboney]

Update!!!!!!
First off let me say thank you for all the input and help that I've been receiving on this form it's been great!
Okay so after looking at both actuators numerous times & messing with all the vent doors and everything, I was about to call it quits. Then my neighbor came over and helped & we realized that my A/C compressor was constantly running no matter the settings. So I disconnected it at the compressor and bingo, I have heat! Now, when I reconnected the butt connector into the compressor if I put any pressure on it (wiggle) any way it turns the compressor off and on. Is anybody experienced this and or do you know if there's any relays or anything else powering that pump might be bad?

 

[98chevy2500SS]

Was the A/C compressor ever replaced or is it still the original? If it's still the original, I wonder if the clutch is going bad.

 

[Jayboney]

Was the A/C compressor ever replaced or is it still the original? If it's still the original, I wonder if the clutch is going baas

 

[Jayboney]

As far as I know it is the O.G. With the engine running if I play with the connector it turns off and on, both male and female sides look fine, I think the clutch is engaging because of an electrical issue?

 

[east302]

It looks like the VCM is providing a ground to energize the relay when the panel is either in defrost or the a/c button is pushed in, engaging the clutch.

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That it cuts on and off when you move the connector implies that there’s an issue at the connector or at the pins. Too, the VCM shouldn’t be calling for it to run if the defrost/button isn’t engaged.

But, you should have heat even with the compressor on. I run mine year round for dehumidification. That you don’t makes me wonder about the signal from the panel to the actuator.

When you disconnect the compressor, what does the heater actuator dial do? Where is the indicator notch before and after with the dial set on full hot?