I can get heat and defrost from floor vents and the defrost area but the button that is supposed to do everything at onc gives me heat everywhere but the vents

Ricardo Loranca

• 552 Answers
• Posted on Dec 05, 2008

SOURCE: heat only blows out of dash vents, will not blow out of defroster

vvacum leak. in back of your temp control unit there is a series of vaum lines attached together they might even be in different colors these lines go to the vent and they open and close them when you slide the lever over this piece needs to be replaced

SOURCE: heater control 98 chevy s10 blazer

These trucks have a problem where moisture builds up in the heater box then freezes. When this freezes and you change your heater settings it breaks the shaft for the blend door. If this is what happened you should be able to look under the dash above and to the right of the gas pedal and you will see two vaccuum accuators one of them you should be able to wiggle around the linkage if it is broke. To fix this you need to remove the entire dash to get the heater box out which involves discharging the AC and draining the coolant because the heater core and evaporator come out. Please rate.

SOURCE: PROBLEM WHEN SELECTING THE DIRECTION FOR THE AIR

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.

SOURCE: heating / air conditioning control stuck to front defrost vents

There is a vacuum leak under the hood. Find the vacuum line on the passenger side where it comes through the firewall and follow it to the engine. You system needs vacuum to operate and without it the default setting is on defrost for safety reasons.

SOURCE: Heat wont blow through heater or defroster vents

Had the same problem. believe it or not i changed the gas cap and got heat all around. something about pressure.