My 2005 GMC C7500 heater is not blowing hot air. The fan is working fine, but it seems we can'[t get it to switch to heat. We replaced the in dahs switch assembly thinking the switch just wasn't...
It is probably the blend doors in the heater case not opening correctly. They are probably vacuum operated doors.
Check the heater core by feeling both heater hoses (the inlet and outlet) when the engine is at normal operating temperature. Both hoses should feel hot, meaning the heater core is circulating coolant correctly. If only one hose feels hot, the heater core may be plugged up, or it may have an air block.
If the heater core checks out good, check the heater case doors for proper movement when you switch from cold to heat. Several vacuum lines branch out from back of the control unit to vacuum canisters on the case, which open or close the various doors. These doors used to be only cable operated, but most are now vacuum operated. There should be a single vacuum hose from the engine, into the firewall, and then to the heater control unit in the dash, where hoses distribute the vacuum signal to various doors or vents as demanded by the switch settings.
Oct 24, 2014 |
Cars & Trucks