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2001 astro A/C stuck in defrost mode

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Anonymous Poster

Jul 30, 2006, 8:24 PM

Post #1 of 3 (1956 views)
2001 astro A/C stuck in defrost mode Sign In

  2001 astro cargo ac /heater unit working in middle two speeds( lo / Hi not working) .Also ac /heater stuck in defrost mode only.
What is wrong and where are the parts located Thanks

Veteran / Moderator
DanD profile image

Jul 31, 2006, 4:24 AM

Post #2 of 3 (1950 views)
Re: 2001 astro A/C stuck in defrost mode Sign In

These are usually two separate problems; a blower resistor controls the blower fan speeds and engine vacuum through a series of vacuum motors control the mode doors directing air flow to the different outlets.
These resistors/relay assemblies are well known for burning out on GM products. You find this assembly behind the right (passenger) side of the dash; 9 out of 10 times it’s the fault of this problem. Before you replace the resistor check that the under hood 30 amp fuse has not blown; this fuse protects the high-speed function of the blower circuit. I would also get the replacement resistor assembly (dealer item) before you begin; this will make it much easier for you to locate it under the dash knowing what to look for.
For the mode doors staying in the defrost; it is most likely the vacuum supply line from the engine that has broken and the mode door has gone to its default setting to blow on the windshield.
This vacuum line is made from hard plastic tubing and can be confused as being a length of black wire; it is the same diameter as wiring used under the hood. It becomes very brittle due to the engine compartment heat and will crack allowing vacuum to escape.
This line connects to the engines intake manifold close to the throttle linkage then comes across the front of the engine to the right inner fender to a vacuum reservoir. This reservoir it tucked fairly low down below the windshield washer and rad reservoir bottles; it is black and round about the size of a grapefruit.
With the engine idling check if there is vacuum getting to and leaving this reservoir. That will tell you what direction to start looking for the break in the tubing. When you find the break in the tubing you can repair it with a section of rubber vacuum hose that fits snuggly over the plastic tubing.
On some models you may have to open up the wiring harness as at times they route this supply tubing with the wiring as it passes through to the passenger compartment.

Canadian "EH"

Anonymous Poster

Jul 31, 2006, 8:17 PM

Post #3 of 3 (1943 views)
Re: 2001 astro A/C stuck in defrost mode Sign In

THANKS Dan Will Let you know how I make out ..

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