Dropped992door
Newbie
I have a 99 two-door Tahoe. I recently noticed about a month ago the AC would start blowing hot under heavy acceleration, or a change in vacuum manifold pressure. There is a solenoid on the firewall that runs from the manifold, and then down to the heater control valve that is between the engine and the heater core. Once the heater control valve, loses vacuum, then it opens and allows heat transfer from the heater core even if the climate control is on cold. If I run a straight hose and bypass the solenoid, you can see the vacuum valve on the heater control valve close. But under heavy acceleration, it will still open back up due to the drop in vacuum pressure in the intake manifold. Is there anybody out there that can tell me how the Vacuum solenoid is wired and or how it works. It is just a two wire plug, I feel that it requires a 12 V signal in ground to open and close the port within itself. I bought a new doorman part and used my Mityvac to create a vacuum in the porch and use the multimeter to check Continuity and there was no change.