My 83 760 heater will not control temperature. The heat is full open. I have tried to do some basic troubleshooting, checking vaccumn lines and operation of the valve in the heater hose. Seem to work ok. I have tried switching out the module under the dash (controls vents) with another module and switched out the temperature controller. Made no difference. (maybe bad too?). I noticed just before this problem started, I could hear a relay chatter, as if a relay was going bad. But that only seem to affect the blower. The blower is working fine too. Does anyone have any insight? Thanks!