I have an '06 Chevrolet Silverado with a 5.3L L33 engine and 146k miles. I have been having issues with the A/C not continuously blowing cold air. It seems to cycle between cold and luke-warm. I have checked the refrigerant pressure and added some to bring it up to around 40psi on the low side (it was down around the 23-24psi range before I started, which I know is low). 40psi is (from my understanding) near the high end of the "full" range. The A/C compressor does cycle on/off without issue. The low-side is cold going into the cabin. The high side is warm (as I'd expect it to be). Also, when the A/C is on, I can hear it "whistle" (does not occur with the A/C off). The whistling will not replicate if I just let it idle and listen under the hood. I had my wife rev the engine a little, and even with it off-idle, I still couldn't hear it under the hood, but my wife was hearing it still inside the cabin. My thinking is, there is a problem with the actuator for the blend door, which I'm assuming is vacuum operated. Does this seem reasonable, or is there something else going on here which I'm not aware of? Maybe someone has some experience with this type of vehicle and it's A/C system.

  • If there are times when it seems to be blowing very cold, I wouldn't expect the blend door to be a issue. I'd expect a partially open blend door to present as consistently non-cold air. May 28, 2014 at 14:26
  • I wouldn't think so, not if it's fluctuating from the heater core to the A/C core ... or at least not closing all the way to the cold side (or maybe at times being completely closed to the cold side, but coming partially open). May 28, 2014 at 14:34
  • Does the amount of revving impact the temp of the air? Is the air always cold until the car warms up? (this could add credence to the theory of a blend door issue, since the heater core starts out cold and warms up.) If the line's cold, I'd expect the evap to be cold, too. When the a/c goes lukewarm, does the a/c LP line go warm too? May 28, 2014 at 14:35
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    Just did some reading -- if the power is pulled, the system will perform an auto-recalibration on the blend doors. Might want to give that a try. May 28, 2014 at 16:37
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    @Paulster2 Some of the forums mentioned keeping the power pulled for 30+ minutes, then having to do multiple drive cycles before the blend doors did their exercises. May 28, 2014 at 22:03

1 Answer 1



This bulletin only applies to Delphi-built HVAC cases, which can be easily identified by visually inspecting the HVAC case from under the passenger instrument panel. The Visteon case is bolted together at the case halves and the bolts are silver in color. The Delphi case will be heat staked together at the HVAC case halves. If prior work has been performed on the Delphi case, the procedure is to bolt the case back together, so you may find bolts of many different colors. If there is any question, check the repair history and drop down the HVAC sound insulator panel to inspect the blower motor assembly. The Visteon blower motor will be bolted into the case. The Delphi blower motor turns inside the case and will have a plastic lock tab on the motor


Some customers may comment on a whistle sound when the blower motor is on and the heating, ventilation and air conditioning (HVAC) control is put into recirculation mode. Other customers may comment that the blower motor stalls out or vibrates or that a "sticky" noise is present during air recirculation door operation.


The adhesive foam used on the air recirculation door (air inlet valve) may not be properly secured, causing some of the foam to contact other HVAC components. The foam could potentially come in contact with the blower motor fan and/or the foam may stick to the inner HVAC case walls, causing the door to stick or hang up.



Remove the blower motor

Locate the partially loose foam, repair or replace as necessary

See here for more detailed instructions

This may or may not be your issue, but it's at least worth a check. Depending on outside air temp, mixing outside air will raise the temp. Leave me a comment if this isn't an issue and I will do some more research.

Oh and to answer your other question it is not vacuum driving actuator. It's a 5-wire bi-directional electric motor that incorporates a feedback potentiometer.

  • This brilliantly describes what is going on (before I've pulled it apart to see). Hopefully this is the cause as one thing which is mentioned in here that I hadn't mentioned is that my blower motor is making a lot of noise ... I didn't think it was pertinent so didn't mention it. Thanks and +1 even if this isn't the fix (but I bet it is). May 29, 2014 at 17:53

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