I'm having a problem with the wifes Montana...the temp control seems to have no effect...it just stays on full hot even if you turn the A/C on or dail it all the way down to cold...I picked up a Haynes manual but it has no info at all on where the heater control valve is located...does this sound like a control valve issue or a dash switch gone bad? The Haynes manual shows how to swap the dash control panel but nothing on where the cooling water is controlled...any help would be great...thanx in advance.

Well, anything involved with heater core and hot/cold air flow is usually mounted right next to it. The flap or actuator that meters air through or around the heater core is most likely the source. No 'cooling water' is utilized in bringing air temps down, air either goes through or bypasses the heater core. Yours seems to be stuck on flowing through it. I'd inspect all the parts to make sure nothing is broke first, if it is fairly easy access.