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Pontiac Repair/HVAC ducting, 1998 Pontiac Transport


QUESTION: There is a "thumping" in the dash that occurs at about 100-120 cpm that seems to come from the HVAC duct work. Changing the air output selection knob does not change the sound except that it stops for a few seconds and then starts up again.  The sound remains the same regardless of the fan speed. It sounds as if there is something flapping in the wind.


ANSWER: Hi Andrew:

is the noise still there is the HVAC is turned off? what is cpm?? is the coolant full in this van? if the coolant is low you could ahve an air pocket stuck in the heater core and that can cause a strange noise and increase as engine speed increases. Noises are hard to find some time they travel and where you actually hear it is not where the root of the noise is. does this have the orignal winshild in it? if the winsshiled was replaced and apoor job was done replacing it there could be a gap in the sealer on the base of the window and the noise.wind is comming in there. with out hearing it I'm just throwing out suggestions as to a possable cause???
good luck :-)

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QUESTION: The coolant is full. The cpm is about 260 cpm. When I pull the HVAC/DRL fuse, the noise stops.


ANSWER: Sounds like either a mode actuator or temp door acatuator is acting up and it is up against one of the stops in the motor and keeps clicking if once you pull the fuse the noise stops it's in one of the acatuators. That is some what of a common issue. they are plug and play parts just unbolt one and put the new one on turn the key to run wait a minute and they self calibarte.
good luck :-)

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QUESTION: Thanks for your help. How does one access these actuators?


It depends on which one it is. I'll assume this is singl zone tem control meaning it only has 1 temp dial. the mode acatuot is on the left side of the HVAc box take the hush panel down under the steering column and you will see it on the side of the hvac box. the temp and recirc actaors are on the rioght side of the dash you need to take the hush panle down and take out the panel the glove box is in and you will see the temp one on the right side of the havc box and the recirc is up by the fire wall at the inlet door. good luck :-)

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Todd Puccio


General auto repair,electrical issues,driveability issues,anti-lock brakes,SIR systems,HVAC,engine performance,Gm specific. I have worked at my current dealership since the 1990 model year anything much older than that I have limited exposure to. I do not have very much transmission experience so those question you may want to ask of another expert. When you send me a question let me know the exact make/model/engine and year for the car or suv you have it makes it easier to answer the questions that way. If your happy with the answer I gave you please feel free to Donate. This is a free service to you and I am not compensated at all by this web site. I have 22 years of experience to share with you and my knowledge wasn't free to me. I had to pay for my education.


Experience in the area: I have been a technician in GM dealerships for over 22 years and I am a ASE master technician. I work at a Buick and GMC truck store Previously I worked at a Pontiac GMC store for 18 years. I Served a a lead technician when dealership was on a team system. I just recently moved to a Buick,Hummer,Saab Store when my franchise was purchased by this dealership. Organizations: ASE master technician


Education/Credentials:High school diploma,2 year vocational school degree 2 year college degree. Associates degree in applied sciences (auto technology)Awards and Honors: GMC master technician

Awards and Honors
Master GMC truck technician Master ASE technician in 9 categories

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