[FIXED] Help. Mazda AC problem? Caused by MODIS?

My AC was working fine (97 Mazda B4000 truck) before I bought a Snap-on modis. I ran a check with the modis and let it run all the checks and it revved the engine up and shut the air conditioner of and on etc… it ran checks on many of the other components… well anyway, my air conditioner never worked properly again. It started blowing hot air during the test. Hmmmm Now it comes on sometimes and sometimes it does not.
I have checked pressure at 39 on low and 165 on high. When it comes on… it is cold and comes out of main vent at 38 deg. sometimes. I have a Mac brand digital thermometer reading it. If it is on it blows really cold.
Once when the compressor cut off, I probed the pressure switch and it had power at both sides. I tested it when the compressor cut off and I had NO power to the compressor wire and had power at both wires on the pressure switch. So my problem seems to be after the pressure switch and before the compressor plug.???
When the compressor was running, I wanted to see which relay under the hood controlled it. I pulled them one at a time while the compressor was running and I could not cut the clutch off. Two of them killed the engine and the third still did not stop the clutch. I am hoping my modis did not do anything to the PCM… Maybe it was just a fluke that it happened when the test was ran. Worked fine before?

Hey tloftis! It sounds like you were running the KOER Self-Test in the PCM, correct? That's the one that ends up checking most of the outputs (idle speed, AC, ect.)

I wanted to take a quick look at the wiring diagram, too. For reference:





It looks like what's in between your pressure switch and the compressor is the WOT relay, which is PCM controlled on the pink/yellow wire. The same voltage from the pressure switches also goes to the PCM as an input on the dark green/orange wire (right of page, #20).

Anyway, I'm wondering if you're right about the Self-Test possibly causing this issue. My first suggestion would be to disconnect the battery and walk away for a few hours. This'll 'reset' the PCM, and hopefully correct any errors created previously. I've had a lot of success using this method. Plus, it's free!

First let me say thanks for this help. I found the problem while testing with t-pins (back probing). I pushed a t-pin backprobe in the harness that goes to the pressure switch that is mounted on the rear of the compressor and found it was loose. Modis had nothing to do with it. You guys always tell us rookies to check all terminals and make sure harness didn't come loose anywhere. If I had done that it would have saved me days of trouble. I had broken the clip that holds the plug in together back when I had to change the heads out and never did anything about it. I just pushed it back on it seemed tight. hmmm well that came back to bite me.

and thanks for the wiring diagram. I am going to print that and put it in my manual.

it is putting out 38 deg air currently. Oh and I did learn several things from you help. One is that the pressure switch is between 24-43 psi. Didn't know that. I guess that means that if I had more than 43 psi in my low side it would quit working?

tloftis wrote: First let me say thanks for this help. I found the problem while testing with t-pins (back probing). I pushed a t-pin backprobe in the harness that goes to the pressure switch that is mounted on the rear of the compressor and found it was loose. Modis had nothing to do with it.

Nice! It's easy to feel silly over something like that, but at least you knew better than to throw parts at it. Self-induced or not, good find.

and thanks for the wiring diagram. I am going to print that and put it in my manual.

No problem. I got that from the BBB Industries site . Tons of free diagrams available.

Ford/Mazda was really great about throwing nice little tidbits into their diagrams on stuff like switches and sensors. The description is a little misleading - the switch will still be closed above 43 PSI. It opens at 24 PSI (to stop the evaporator from freezing), and closes again at 43 PSI. As Paul would ask, "Make sense?" :lol: