Hi i have an 89 chevy 1500 2wd, it came up from flordia but is now in michigan. Anyways for some reason on the vent controls (HVAC) when i press a button to change from head to feet or from hot to cold everything will just flash and blink. Sometimes it changes sometimes it doesn't. I also noticed that when changing from hot to cold it is either hot or cold no real mixing. I got a new unit from the junk yard but same problem. I heard there could be a bad ground causing this but not sure. Any ideas? I really don't want to drop over $100 into a new unit if its not going to change anything. Thanks sry for the long post

 

Hard to say but I know those controllers are notorious for going bad. Look at the plug in the back of the controller and make sure it looks clean and none of the prongs are bent over.

 

Does anyone know a cheap place to purchase a new unit? I think at my dealership it was around 150. Obviously i have already tried one from a junkyard with no change, hard to tell what the problem is if you don't know if the one you put in works.

 

Your blend doors are separate from the AC controls? As in switching the air flow from windshield (defroster) to through dashboard to feet? Sounds like the dashboard unit itself.

 

I attempted to fill my AC with R134 but the clutch on the compressor quit cycling on and off during the fill process. What happened and how to fix it? I did replace the AC cycling switch and the dashboard control module (other reasons). According to the instructions i was supposed to let the AC compressor run longer before attempting to fill the system with refrigerant. I can run a bypass directly from the battery to the AC clutch plug and the unit engages but it wont work from the dashboard.

 

hey i still have not found the problem with my vents not working properly. I replaced the motors and the control unit with no different results. So i guess its in the wiring somewhere. Anyone have any advice on pulling the dash to check the wiring? Do i have to drop the steering column?

 

Goldenhammer did you check the fuse under your dash??

 

as far as i know i have checked all the fuses. I checked the fuses that are on the dash and checked around. I don't know if there are any more anywhere else but it still has power going to it so i don't think a fuse is blown.

 

in a word, yes. You have to drop the steering column but its simple there are only 4-6 bolts. The problem will be locating the main bolts that hold the dash to the cowl. Every model is different but there should be a large tube that goes from side to side. That has to be removed or dropped down, then look under the passenger air bag or glove box area you can tell coz they are 15mm or bigger. Just remember what bolt came from where. Get a block of styrofoam and 'plug' the bolts, screws etc into the styrofoam as you go. This way as you're putting it all back together you have everything right there in front of you. You replaced the blend door actuators? Check the linkage and the ground right? All that could be left is a relay, fuse or the unit itself. I can assume by your question that the unit is getting power, i dont what else to check man. Every now and again you run into those brain stumpers, when i hit that wall i back up and do it all over again. Step by step, you'll find a step you missed along the way.

 

There's two fuse boxes right? Under the dash and under the hood. Can i unscrew the AC cycling switch and manually depress it without the system being full of refrigerant to fool the compressor? Like i said i dont think its the compressor because i can run a jumper pair of wires directly from the battery to the AC compressor on the electrical plug that goes into the clutch and it turns on. Even if the engine is off i can hear a loud 'clang' as the clutch engages.