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I just got this Blazer running today and took it out for its first drive in at least a year and a half. Now that it’s running, I’m looking for anything else that’s wrong with it. That’s where I found this problem with the HVAC when when I set my controls to the cold end on the temperature knob, hit the AC button, and set the mode/zone switch to vent. I got heat and it would cycle from warm to hot air. Then I turned the temperature knob over to the hottest end and turned the AC button off while leaving the mode on vent. The air blowing out still cycles from warm to hot. The coolant was topped off prior to this test drive. I can’t recall hearing the compressor actually engage, but failed to pay better attention once I observed the other symptoms. I probably won’t get to look at the truck again before next week. But I’d love to hear ideas about it. It’s an LT and it looks to be fully loaded on all the options. The controls aren’t digital, but they do show specific temperatures on the temp knob. There is some kind of auto control button that I didn’t bother to study more closely yet. And, I’d just assume there’s going to be a sunload sensor somewhere in the mix. So whatcha think?
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Try turning on the ac to max and put it in recirc mode to see if
the compressor engages. If it does not I would suspect low or no
charge.http://www.ericthecarguy.com/faq/solving-automotive-hvac-problems
I can hear the temperature blend door moving back and forth as the air changes from ambient to hot. I don’t hear any popping noises.
I can almost guarantee you that for the year it’s either low on freon or leaked it out. Hence the ac no work. You’d be better off checking on comp engagement, before posting any Q-s on ac. It’s basic test.
Well like I said from the start, the cycling from warm air to hot air is happening regardless of whether or not the AC compressor is actually turned on. I’m not chasing a refrigerant issue yet, but that is on the to do list. What I am chasing right now, I believe is a problem with the temperature blend door actuator.
Some more snooping on the internet apparatus pointed to the electronic blend door motors as a pattern failure part. I decided to pull mine and cracked it open to find something else already cracked open. The large sprocket had shifted about 30° which I’m guessing caused the module to lose the potentiometer signal and left it hunting to find the correct signal. There are other stories that tell if the sprocket cracks in the right spot, it can bind with the middle sprocket and leave it seized altogether. Be careful if your turn comes around to buy a replacement yourself. There are two motors; one of which is for manual heater controls and, of course, the other the automatic control. Rock Auto has the Dorman actuator for about $85 (Part # 604-106) The actuator is tucked up on the case behind the glove box and is in a very tight space. It is still accessible even if you’re equipped with hooves for hands. A quarter drive flex head ratchet with a 7/32 socket gets the screws out. Some strategic prying might be necessary to lift the actuator far enough in that tight space.
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Usually you hear a popping noise under the dash when the gear cracks… I should have made myself a little more clearer on my post..
Your post was fine. The actuator would cycle back and forth regardless of where I set any knob. I could hear the door moving back and forth, but with no sound I could qualify as a popping noise.
Good find! Thanks for keep us up to date and showing the fix. Just for good measure I’m going to link my article on HVAC here for future reference.
http://www.ericthecarguy.com/faq/solving-automotive-hvac-problems
Seriously good work and excellent post.
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