Pontiac Repair: HVAC ducting, 1998 Pontiac Transport, hvac duct work, hvac ducting

Question
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.

Andy

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 :-)


---------- FOLLOW-UP ----------

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

Andy

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 :-)


---------- FOLLOW-UP ----------

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

Andy

Answer
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 :-)