Hello All,
I have a 1998 Blazer 4.3l 2wd with Automatic Climate Control. Whenever I push the A/C switch it blinks 3 times and then goes out. I have searched this forum and have checked the low pressure switch, high pressure switch and the ambient air thermister and all are good. The freon charge is good. If I jump the wiring on the compressor and run the A/C all pressures are right where they are supposed to be. Also it appears vacuum is good since I can switch air to defrost and side vents with no problem. Last sometimes the A/C will work just fine and I can make no rhyme or reason as to why it does or it doesn't work.

I am thinking maybe the control panel but dont want to spend the money unless I can confirm that it is the problem. Any and all help is GREATLY appreciated.
Thanks,
John

 

I am having a similar issue on a friends '97 GMC s-10 Jimmy and think it has something to do with what she has described as "a cable behind the dashboard linking to the 'flutter valve'". Apparently she has paid $30 every change in season (i.e. start of winter, start of summer) to have a mechanic manually move the 'flutter valve' by reaching through the now permanently removed glove box.

 

Okay, at one point I had the same three flashes on the A/C button, but here is what I did after I found a post on another site, with the problem titled: "Blend door (with pictures and common problem): Blend Door (with pictures and the common problem) How-to | Technical Info - Car Questions, Answers, and Discussion
There is a small plastic door inside the ductwork behind the glovebox on the 2nd gen S-10/Jimmy. That door is operated by an electric motor located directly on top of the ductwork (and behind another actuator which changes air from floor to face blowing). When that door was stuck in the heat position, the light on my AC switch flashed three times and went off and all I got was hot air. The part is held on by three, or in my case two, screws. My 3/32" was too small and my 1/4" was too large, but a 6 mm worked. I used a 1/4" rachet with a pivoting head and a short handle. The motor assembly fits over a round gear like shaft, and the gear inside the assembly had broken, therefore slipping on the shaft. I was able to remove the two screws and gently pry the assembly up and off the shaft--- the electric connection had previously been removed by a mechanic. The referenced link has pics and so forth.

 

Thanks for the reply. I wish this was my problem but my blend door works fine.
After some more extensive troubleshooting I believe something is telling the ECM to not allow the Air to come on. I say this because I temporarily wired a switch in between the power to the ACC and the signal to the ECM and when I switch it on the A/C Compressor comes on for a second and turns right back off. When I did this I had the ACC computer plug removed from the back of the ACC.
I am REALLY LOST on this one!!!!!
John

 

Mine did the same thing...low freon level was my cause. I think there could be multiple reasons for the flashing A/C light and it's just telling us that something is wrong without being specific. If you follow the procedure here for recharging the system there's a pressure switch on the A/C canister that can be jumpered. If the compressor comes on it might be time to add a little freon. It's not a good idea to run the compressor very long without freon and/or lubricant. I'm just a hack backyard mechanic so get the opinion of one of the experts.

 

I really appreciate the help. If it wasn't for us backyard mechanics most of these forums would not be around. it is us most of the time that ask the questions we all want and need to know. I tried jumpering the low pressure switch but that did not help. I know the charge is accurate as I just fully charged the system. Something is telling the ECM to not allow air, I just cannot figure out what. Again thank you.

 

I have the same problem with the blinking light, it only does it when it gets really hot out, usually after I have parked it, its only cut out while driving once or twice. I noticed that when I get moving on the highway the AC kicks back in and the light stops flashing. Maybe something to do with air flow?

I had an ac check/charge done a couple months ago so I'm going to have them recheck it, hopefully its just low on freon. I had the blend door replaced a couple years ago so I dont think thats the culprit.

 

How have you checked the low & high side pressure switches? I believe that the low pressure cycling switch is a normally open switch that closes when the pressure is in excess of ~26psi and that the high pressure switch is normally closed and opens when pressures exceed ~300psi. The AC request signal is sent to the PCM from the HVAC control panel through the high pressure switch. The PCM requires a +12V (if I remember correctly) signal from the HVAC control panel through the high pressure switch as well as a ground signal through the low pressure switch to then energize the compressor clutch relay.

A blinking light typically is caused by a problem in the compressor clutch circuit (as in an open high or low side switch). If the switches are both closed and the compressor does not engage, I would start back tracking through the wiring. Check continuity from the switches to their respective sources (be it ground or the hvac control module) and then to the PCM. Also, check the wiring from the PCM to the relay, but I doubt that is the source of your problem.

From your description 88skisupreme, it sounds like your system is triggering the high pressure switch which is disabling the clutch to prevent damage to the system. This could be due to an overcharge, inadequate cooling of the condenser, a few other problems within the system, or a combination thereof.