Hi everyone. New to the site. I hope I am doing this correctly. A friend directed me here in search of an answer to my heat / AC problem on a 97 AWD Astro. The heat/AC control on the dash does not seem to work and air is only coming out of the heat vents. The compressor will start when the selector is switched to defrost or ac but will cycle on and off but the air flow does not change. I have replaced several cracked or broken vacuum lines with no change. The weather here (Northern Harford County, MD) just went over 90 plus, so I need to fix before summer. I have the dash torn apart and all the duct boxes are exposed. I have used a Mityvac on the control and can hear air flow change and air speed increase but still no air thru the dash vents and the AC compressor will not continue to run.
A cold beer for anyone who can help!
Have the system checked to make sure the system is "fully" charged. The cycling on and off is a key to low refrigerant. Please keep us updated, Thanks.
Thanks for the response. I probably wasn't clear about the symptoms. The air blows from the heat duct only no matter where the selector is pointed. When the selector is pointed to AC the compressor will kick in and then cycle on and off, but the air flow still does not change. Outside air does not flow through the vents. The primary problem seems to be the inability to change temp or air flow control which I believe is likely due to inoperative damper (vacuum) control. The AC might also be low on refrigerant as well, but that should not affect the damper control.
I think I need to find a vacuum leak or other problem. I have replaced a few vacuum lines with no improvement. Is there a way to test the control unit in the dash?
This sounds like the typical vacuum hose break that causes everything to blow through the heat vents only. On my '98 I had to remove the engine cover and find a very thin plasticy type vacuum hose that runs from very near the PCV valve area at the left rear on top of the engine, intake manifold. Depending if its broken or just leaking, it might be in two parts by now. It runs across the top of the engine towards the front right corner. There it goes in to a Y type fitting I do believe, in the area around where the heater/ac box protrudes out of the firewall, and slightly low down, need flashlight. Its been years since I did mine. I replaced it with rubbery hose instead of the brittle plasticy stuff.
Here, some others have more detail in the thread further down this section.... viewtopic.php?f=34&t=1265
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