No Heat 87 420SEL

[jriewer]

I have suddenly lost all heat when idling or moving. No heat when the defroster is turned on, (it justs blast cold air) or when pressing any other buttons on the CCU. The blower motor behaves properly, the A/C compressor kicks in when it is supposed to, and the A/C will blow cooled air when the temp dial is turned to the blue. I just can’t get any heat! I pulled the mono valve and cleaned it and tested it and it works properly. I’ve got the CD manual but cant figure out where to start trouble shooting this problem. All the postings I’ve found relating to a no heat problem usually indicate that the defroster setting still blows hot air but that’s not the case here. Any suggestions? Im gonna pull my glove compartment and look around back there but Im not sure what to be looking for. Thanks