r/Hummer • u/TheFixer2019 • 8h ago
Hummer H3 Cooling System Air Removal
galleryRecently replaced the water pump, engine coolant sensor, secondary air valve, and thermostat and housing. Needless to say, the system was completely evacuated and therefore a ton of air in it. I know have coolant behind the engine side of the thermostat, coolant filled on the radiator side of the thermostat, radiator is filled, suction hose to reservoir and reservoir have coolant.
I filled the internal engine coolant passages between the radiator and the outlet side the beat I could by removing the hose from the radiator top side and pouring coolant in through the hose.
In my mind the air that could still be trapped in the system should be minimal, but I keep experimenting a temp gauge that goes to about 1/8 above cold and holds and then drops to cold and the dreaded AC Off message pops up.
I've tried to burp the system using the radiator cap off method, the lifting the front end method, and now the coolant system pressure test/fill kit method with the venturi assembly. The message still keeps coming up on the dash. When I used the vacuum method, I got the vacuum down to 20 inHg with the compressor connected and running and the lever open on the vacuum assembly. When I closed the compressor lever, it dropped to 10 or so. When I open the coolant line to allow the vacuum to draw coolant in, I have been able to get it to draw in 1/2 gallon before vacuum returns to normal. I like in Denver so high altitude and thin air.
Help please! I feel like I'm likely missing something simple or that there's a method that I haven't come across that will finish this and get rid of that AC Off message once and for all.
Thank you in advance for the expertise and direction!



