My 99 gmc wont blow heat on floor. on 1999 GMC Jimmy

My heater blows heat out vents and defrost but when switched to floor alone or like floor and vent it just blows out the vent and when set to floor only it moves to the defrost I'm assuming its a vacuum issue so would be great to figure out where n whats causing this issue.

by in Newcomb, NY on December 20, 2011
1 answer 1 comment
ANSWER by on December 20, 2011
Vehicle Application: 1999 Jimmy 4.3 Customer Concern: Cannot get any air to be delivered from the floor. All other positions seem to deliver air properly. Tests/Procedures: 1. With the climate control panel on the heater or floor position, check for vacuum on the Red and Yellow vacuum hoses. 2. Should no vacuum be present from one or both of the hoses, check the following wire to be sure they are grounded by the climate control panel. They are Purple and Tan wires, and both should be a ground. If one is grounded and the other one is not, the control head would be at fault. If both wires are grounded, the solenoid assembly is at fault.
COMMENT by on December 20, 2011
just found out when changing the climate control from only floor to defrost i can hear a clunk like door shut noise only when putting back on defrost so i think its not opening all the way cause i get very little air out the floor vents so idk whats going on.

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