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Full Throttle Intermittent AC

GammaRadiation on Mon June 29, 2015 12:28 PM User is offline

Year: 2000
Make: Mazda
Model: B3000
Engine Size: 3.0l
Refrigerant Type: R134a
Ambient Temp: All
Pressure Low: 40PSI
Pressure High: 250+
Country of Origin: United States

Hello, I have a Mazda B3000 with an AC that hasnt been operational for 10 years. I am refreshing the vehicle for daily use and would like to solve this AC problem.

When I initially checked the charge it has less than 100psi static and the compressor would cycle every 3-5sec. I added a small can of oil and enough refrigerant to raise the low side enough to keep the compressor on at idle.

Now whenever I go full throttle or high load in general the compressor shuts off as it is supposed to but it does not come back on unless I leave it off for a while (20min seems to do the trick). I have replaced both pressure sensors and that did not resolve the issue.

If I have a leak it is VERY slow, no change in operating pressure after two weeks of use, dealing with the intermittent AC.

I believe it is either the WOT cutout relay or the TPS sensor. However, the truck runs fine in open loop and exhibits no other symptoms of a potentially bad TPS. Mynother option is overcharged but I have normal low side pressure for the ambient temps.

Please help! I am taking it on a road trip and FL summers are HOT!

Vent temps are in the 50s on full blast fan and just below 40 on the lowesr fan setting.

Edited: Mon June 29, 2015 at 12:42 PM by GammaRadiation

GammaRadiation on Wed July 01, 2015 8:20 AM User is offline

32 views and no responses, I guess you guys are as stumped as I am. I guess its time to take it to a professional who can recover all of the refrigerant and refill with the known correct weight.

Dougflas on Wed July 01, 2015 11:34 AM User is offline

First thing you need to do is make sure the correct charge is in the system. recover and weigh in the correct charge. You may want to do a leak check first.

AC_Doc on Wed July 01, 2015 5:18 PM User is offline

I'd be looking for the Wide Open Throttle (WOT) relay that controls power to the clutch coil. This relay is probably located in an engine compartment CCRM riveted closed module case. If so, you'll have to drill out the rivets.

Among several other relays there, you'll likely find that the WOT relay is soldered into a circuit board and the relay plastic case looks like its been overheated. Might also look at the solder connections of the relay to the board. These connections tend to crack from repeated thermal cycles heated by the coil current passing through them.. When it gets too hot the solder cracks open up and drop the power to the compressor clutch coil. When things cool down, the connection restores and the clutch works for awhile. Also likely the power contacts on the WOT relay are worn, corroded, and intermittent.

If you're competent with a solder iron you can replace the relay.

Good luck.


Sometimes you must accept things at faith value!

GammaRadiation on Tue July 07, 2015 9:13 AM User is offline

Thanks for the suggestions!

After reading through here for a few days I couldnt find another thread with the exact same symptoms, however I did pick up a trick or two. After the AC cut off I pulled over and tapped the front of the clutch with a plastic flashlight and sure enough it came back on. So I believe the air gap changes just enough after the compressor warms up to prevent the clutch from engaging. I am going to try taking the clutch apart and removing a spacer. If that doesnt work I will try changing the relay. Unfortunately none of the local autoparts stores have one in stock. Ill report back once the AC is fixed.

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