Questions and Answers

Mazda B-2300 A/C Problem? Q. I have a 1996 Mazda B-2300, manual 5-speed about 70,000 miles, fuel injection, P/S and A/C. the problem is with the on dash switch. When I turn the switch to the right to get heat at the first setting I get heat but I can also hear a "click" as the A/C clutch engages the A/C compressor and then an increase in engine rpm, it decreases after a few seconds.

This occurs again intermittently every few minutes as I idle or drive. The problem doesn't happen on the next setting, the floor setting; but occurs on the next two heat side settings. When I turn the control knob to the a/c side settings, I get the "click" as the A/C clutch engages the compressor and the rpm change but this is to be expected and would appear to be normal.

But why do I get the clutch engagement and rpm change when I turn the control knob to the heater settings? Any help Mr. Vince? Excellent site, one of the very best.

Thank you...

A. This is the description and operation for the 1996 Mazda B-2300 truck as outlined by Mazda.

Blower Controls
With the ignition switch in RUN, voltage is applied to the blower motor. With the blower switch in OFF, there is no ground connection to the motor. When the blower switch is in LO, current flows through three resistors to ground. In MED-LO, current flows through two resistors to ground. In MED-HI, current flows through one resistor to ground. In HI, current flows directly to ground.

A/C System
The A/C system is turned on or off by depressing the blower switch. When the blower switch is depressed and latched, current flows through the A/C switch, the clutch cycling pressure switch and the WOT (wide-open throttle) cutout relay to the A/C clutch field coil. The clutch engages and the A/C system turns on. The A/C ON indicator light in the switch illuminates. When the switch is depressed again and disengages, current to the NC clutch field coil stops and the indicator light turns off.

A separate micro-switch inside the A/C-heater control assembly automatically engages the A/C clutch, but not the A/C On indicator, when the defrost mode is selected.

The A/C system is monitored and regulated by the powertrain control module (PCM). The PCM, working through the WOT cutout relay, disengages the A/C clutch under any of the following conditions:

1. Immediately after start-up
2. During wide-open throttle conditions to provide extra engine power
3. When engine coolant temperature approaches an overheating condition
4. When engine idle RPM approaches stall speed
5. At high engine speeds

So it seems that the system is working as it should. From your description I can't tell if the A/C compressor cycles on and off excessively. If this is the case, then the system is probably low on refrigerant and should be checked for leaks and topped off.