[s-type] Heater problems

My heater only blows cold. I have dissconnected the quick release
pipes near the front of the engine, flushed and reverse flushed the
matrix and all runs fine. I have however, noticed that the heater
matrix is situated higher than the bleed valve and suspect that my
problem is due to an air lock in the matrix. Any suggestions on how
you can bleed the matrix?–
Peter Lambert
Twickenham, United Kingdom
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Hi. Apparently this is a very old question. However mine is a real time issue.

I have a 2002.5 S Type 4.2 N.A V8…purchased November 2017.
Hadn’t noticed until a recent cold wet day but no warm air getting to cabin/windscreen.
Blower works fine and all registers respond when selected.
My water pump failed recently and I replaced it.

I then decided to replace the Thermostat, Auxiliary Water Pump and Dual Flow Valve.

The Aux Pump has a fuse and Relay but I cant find anything for the Valve.

I’ve also noticed that the middle aluminium pipe going to the heater gets hot but not the other two.

The manual says the solenoids “are individually actuated by the Heater Control Module”

Any advice on where this is and how to test it, or any other information would be appreciated.


Hello again…still chasing my lack of heating problem. I have an Error Code
“Cold Air Bypass Actuator Circuit Failure”( my main control board has been checked and is OK) Plenty of youtube posts suggest a faulty actuator is a common point of failure. I’ve been trying to find a part. AC Delco is mentioned on youtube. Does anyone have a part number or information on where I can get the correct actuator( VIN M52021 )
Any other help regarding replacement would be appreciated.