Heater not working

[manger]

Okay, I turn the temp dial to full heat and then select windshield defrost and the AC comes on? have not checked a fuse yet. I have had a lot of rust in the coolant and had to flush the heater core. I have had the heater working recently but leaked coolant at some junction where the heater core hoses met (intersection with a built in vacume powered valve) have not tried the blend door check yet. I'll repost after checking fuse, blend door, and heater core blockage. but why is the AC compressor engaging when heat is selcted?

 

[martin]

It comes on by default when you select defrost, it de-humidifies the air and makes the defrost more effective.

 

[Downey]

the rust in coolant sounds like you have a plugged heater core

 

[manger]

nope, its the plastic valve between the engine and the heater core, its sticking in the closed position. i'm gonna call it the heater core bypass valve. anyone know more about this system?

 

[manger]

its called the heater control valve and its part number FS7218495-AA. its vacume operated. How do I check to make sure there is proper vacume at the valve?

 

[maverick1970]

its called the heater control valve and its part number FS7218495-AA. its vacume operated. How do I check to make sure there is proper vacume at the valve?

Yeah I need to know about this too. I've been troubleshooting why my heats not working and I've discovered that the vacuum line was off. Don't know how but it wasn't connected. From the looks of the vacuum line, it looks like it melted. My guess is that it got too close to one of the heater core hoses.

 

[maverick1970]

I reconnected the vacuum line and the heat is still not hot only a mild warm. My guess is that I've got a clogged heater core??? Not sure.