No heat, recent dash removal/radio install...

[mygt8a4re]

Just to start off, my coolant level is fine and everything is operating normally, not a case of head gaskets/oil coolers/low coolant(studs/gaskets/egr delete done in January).
I recentlly did a new head unit install and had the entire dash out and all plugs harnesses removed (2 months ago). Today I went to turn the heat on and it just blows cold. At normal op temp, no matter how long the engine is running, regardless of rpm, there is no heat, just blows cold. All vents blow at thier designated location when switched to & a/c works perfectly. I popped the dash out w/o disconnecting any harnesses to see if I could find a loose connection today when I got home from work. Everything looked good behind the control switches for air/heat/fan/etc and there were no disconnected or crimped vacuum hoses....
So, Im trying to find where to look and what to do next. I cant get the thought out of my head that I did somthing when I had my dash apart a couple months back....
Any input is appreciated!

[ZMANN]

well the heater bypass comes to mind // it's under the hood and near the oil fill it should default to open when no vacuum but they have been known to fail closed

[mygt8a4re]

Originally Posted by ZMANN

well the heater bypass comes to mind // it's under the hood and near the oil fill it should default to open when no vacuum but they have been known to fail closed

Thanx ZMANN, Im not familiar with the heater bypass or how it works, does the heater bypass "bypass" the heater core? when open it allows the coolant to stay flowing to the core and if closed it bypasses the heater core alltogether?
thanx for your input!

[ZMANN]

yes it will block coolant flow to the heater when max AC ( recirc) is selected

easy to find under the hood .. it has a vac line running to it ,, just right of the oil fill tube

[mygt8a4re]

Just went out and checked it, the vac line is connected. when I pulled it off the little actuator moved outwards and when reconnecting the line the actuator pulled back in. Im assuming this is operating normally? thx

[mygt8a4re]

Ok, I ran a little test on the heater control valve. When the truck is running and at operating temp, the control valve arm is pushed out. It stays out if I have it set to hot or cold on the temp knob and also stays out if i pull the vacuum line off. When I shut the truck off the arm on the heater control valve pulls in and stays in. So now Im unsure on my next move. Is the valve working properly? Am I not seeing vacuum in this hose due to the hot/cold control knob malfunctioning? Holp this helps someone to offer input on my situation...thx

[mygt8a4re]

Ok, i ran yet another test if this helps. This morning I ziptied the valve on the heater control valve thinking it wasnt getting vacuum, thus Id feel some heat but I got the same results, cold air. So, it doesnt matter where I have the temp dial or wich way the heater valve is oriented it just blows cold.....hoping somone can chime in with some suggestions.....

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[snafu!]

Check to see if the heater core is getting warm, just to make sure it's getting circulation. There are just a few screws in the cover behind the glove box. If it is getting hot then you have an electrical issue somewhere. Also the heater bypass under the hood should stay open unless it's on max a/c. there is also are two vacuum lines right to the left of the heater core with a disconnect to allow removal of the heater core, you may want to check that.

[mygt8a4re]

Excellent info, Ill check that out this morning. Thank you for your help!

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[mygt8a4re]

I wanted to come back and thank you guys for your help. I went through the loops and narrowed it down to the control motor or the door blend motor. The auto parts store had the door blend motor for $35 so I decided to swap it and it worked.....