5.7 tbi Running Cool and No Heat

[Dave_N]

Just to answer this question, the valve closes when the temperature dial is set to the “max” cold detent. This energizes the solenoid to apply vacuum to the valve, causing it to close. It is normally open. Test operation by pushing the spring loaded plunger “in” to close it. It should spring back down when released.

Closing the valve prevents coolant flow to the heater core and is meant to maximize a/c performance. My dash vent temps drop about 5-degrees when this is done.





Sent from my iPhone using Tapatalk

Thanks for this answer. I figured out pretty quick after my original post that the open position was actually the normal position for the valve, but I still hadn’t figured out what sent the signal to solenoid.

 

[Dave_N]

How difficult was it to install the new heater core? I understood you had to pull the dash to do it in that body style Yukon and Suburban. I have a '99 a know this day is coming at some point. Just curious if you had to pull your dash since you mentioned doing it in an afternoon.

It was actually super easy. You dont have to pull the dash. Just drop the bottom cover on the heater box, under the dash. It’s held on by like 5 or 6 metric screws. 5mm I think, but not sure if I’m remembering the size correctly. I’d recommend picking up a foot each of 5/8” and 3/4” hose at the parts store when you get your core, and replacing the hoses between the core and the control valve. I found it easier to just cut them off with a razor knife and replace them than to fight with getting them off of the corroded heater core connections. The whole job took about an hour, but I spent at least 15 minutes of that cleaning out junk that had fallen through the broken plastic grating over the defrost vent, into the heater box, jamming the defrost mode door open (PO used it as a beater work truck).