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No heat. Where's my heater control valve?

Old 12-06-2016, 05:06 PM
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Default No heat. Where's my heater control valve?

Hey, guys--Need some help here. My heater doesn't work, or at least blows luke warm air at the most. I have a new water pump, new thermostat, new blend doors, my blend door actuator is working, I even pulled the heater *** panel off to make sure everything is connected. In addition, I back-flushed the heater core with a garden hose (what came out didn't look bad at all and there seemed to be steady flow coming out). But not sure I used enough pressure?

BUT, my heater remains barely functional, and usually doesn't work at all. Any ideas? I was thinking about checking my heater control valve next. It's getting cold outside and it SUCKS driving and freezing my butt off! PLEASE HELP!
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Old 12-06-2016, 06:18 PM
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Welcome to CF!

If you're talking about a water flow control valve, it doesn't have one. The heater core is a full flow design with temperature controlled by the air coming thru blended with outside air. (Thus the "blend" door). If both heater hoses are getting hot, you've got flow thru the core and the problem must be either an air blockage in the core or air supply to it.

To get air out of the core, make sure the hose from the thermostat housing goes to the lowest pipe on the core. That way the air will bleed out thru the water pump naturally.

Just for grins, try switching the mode control to recirculate. If the air gets hot then, it's a problem with the internal air control doors. Also, check the vacuum supply line from the engine compartment. The blend door is controlled by an electric stepper motor, but the mode selector is vacuum controlled. This line comes off the intake manifold and "t"s at the firewall to go to the heater and cruise control actuator, then "t"s again to go to the vacuum accumulator. Without vacuum, the heater goes to a default setting of defrost.

All this is for the manual heater and not for the climate control heater.

Last edited by dave1123; 12-06-2016 at 06:23 PM.
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Old 12-07-2016, 12:06 AM
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Edit: Never mind. I stumbled into the wrong forum again.
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Old 12-07-2016, 02:46 PM
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Thank you for the quick detailed info! I'll give it a whirl and will hopefully pin point the issue
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