Excessive heat

phatz_hatz · Mar 31, 2026

Flushed whole cooling system today, replaced thermostat, thermostat housing, upper and lower hoses, and this “heater valve” with the AC on it seems like it’s not diverting the coolant back into the cooling system and just going into heater core thus making the AC struggle to work cause it’s blowing through the hot heater core. Unsure if it’s related to replacing it, it’s. GPD heater valve right now have it zip tied to so i get AC. Could it be the vacuum motor, or the switch inside the cab

Eman85 · Apr 1, 2026

!997 Tahoe when my valve leaked I installed it in the garbage can and just ran 2 heater hoses, AC works fine. My PU never had a valve and AC works fine. If you're worried about max AC put a manual valve inline and shut the water in the summer.

exp500 · Apr 1, 2026

Also check vac line for breaks, loose connection.

phatz_hatz · Apr 1, 2026

Eman85 said:
!997 Tahoe when my valve leaked I installed it in the garbage can and just ran 2 heater hoses, AC works fine. My PU never had a valve and AC works fine. If you're worried about max AC put a manual valve inline and shut the water in the summer.

Been thinking about this or running a vacuum line straight to intake manifold to bypass the control solenoid. The solenoid isn’t getting power from the switch inside the cab, or it works intermittently cause it worked sometimes before that, so it’s not activating the vacuum

Eman85 · Apr 2, 2026

System wasn't the best on the day they were new. Not worth the trouble and like I said PU's never had the valve.

east302 · Apr 2, 2026

Just making sure, you had the temperature dial in the “max” detent when checking for voltage? And the vacuum line from the solenoid to the PCV fitting is intact?

LsHart · Apr 2, 2026

Possible vacuum manifold, aka the module?

phatz_hatz · Apr 8, 2026

This is what i came up with after testing the power with the ac on full blast and still wasn’t getting it to power. Ran all new vacuum lines to everything, put a 1/4 valve from back of intake manifold directly to heater valve turn it off for winter and on in summer. Simple fix

Excessive heat

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