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2000 Oldsmobile bravada: heat blows..switches..cold air for approx

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I have an 2000 Oldsmobile bravada that I'm having heating/cooling issues with. The heat blows for approx. 10 secs and then switches to cold air for approx. 3 secs. when the AC is on. When AC is off, Heat blows all the time no matter what temperature is set at. Already checked the vacuum to the actuators. They are fine. Thinking that it may be the module but don't want to spend $400-$500 if that's not the problem. Could you please advise further? Thank you in advance for any assistance you may be able to provide me in troubleshooting this problem!
Do you have auto or maunal a/c controls?
Customer: replied 8 years ago.
It's climate control but you have to manually push a separate A/C button for it to work.
There is a eletrical actuator that controls the temp door. This is most likely the problem.The controller does not do muchwork, it tells the actuator was to do. The actuator does the work and tends to go bad, there are sensors inside of the actuator that wear out. I think you have to remove the dash to gain access to the actuator.

HVAC Vacuum Control Solenoid Valve Assembly and Electric Actuator

Object Number: 556999  Size: FS

Heater/Vent Module Connections

Object Number: 393159  Size: MF

(1)Electric Actuator (Temperature)
(2)Electric Actuator Connector
(3)Splice Pack SP200
(4)HVAC Vacuum Control Solenoid Valve Connector
(5)HVAC Vacuum Control Solenoid Valve

Object Number: 392686  Size: SH

MPMoore and 2 other GM Specialists are ready to help you
Customer: replied 8 years ago.
Is there anyway you can call? (XXX) XXX-XXXX

Since I already tested the actuators, I would like to tell you what they during testing.
Customer: replied 8 years ago.
Not sure what the rules are here so if that's not an option then I checked the actuator and it was opening and closing.
The phone nuber does not come up, and it is against the rules for me to do so.

The actuator may be moving, but it should move then stay in one place when the temp is set, it should only move when you change the temp setting.
Customer: replied 8 years ago.
Ok, I have checked the vacuum actuator right in front of the one pictured above. Its the actuator that changes floor/vent/defroster. Have not checked the electric actuator. Is that the one you are referring to? The one right behind that vacuum actuator.
Yes, that is the actuator (eletrical motor) that controls the temp.
Customer: replied 8 years ago.
Ok, then I will try that this week. Will the case close after a certain amount of time or do I have time to accept the fix by logging back in after the electric actuator (electric motor) has been changed and I know it works?
It will close due to time, but you can go back in and accept the answer. It will give me credit if you do so at a later time. Let me know what happens.
Customer: replied 8 years ago.
I'll keep you posted...thanks so much for your help!