Intermittent A/C

2000 standard cab started having intermittent A/C operation. Truck has 99k miles on it (belonged to my 91 year old dad).
Of course when I go to troubleshoot it, the AC works fine. The repair manual that I downloaded from Tacoma World says the wire (pin 9) coming out of the AC amplifier going to the compressor clutch should have less than 1 volt when compressor clutch is engaged and zero when disengaged. I read battery voltage (13.8v) when the clutch is engaged and zero when disengaged. The strange thing is that the ac is working with 13.8v on pin 9.

I’m wondering if there is a misprint in the manual?

Anybody have this issue?

Thanks! bf

 

I can't comment on the voltages, but a lot of people have this issue. Try moving the hot/cold mix from hot back to cold and see if that makes the A/C blow again. If so it's likely the blend door actuator / servo motor.

 

Must be a misprint, Pin 9 controls the A/C clutch so it should have battery voltage when the clutch is engaged.
Need to catch it acting up and see what's missing.

It's a fairly simple system, power comes from the 10 amp A/C fuse to the A/C switch and dual pressure cutout switch, when the switch is turned on it sends it to the A/C amplifier as the A/C request signal.

To enable the compressor the A/C Amplifier needs 4 signals, A/C request signal on Pin 5 (Black/Blue), power from dual pressure cutout switch (opens below 29 psi or above 455 psi) on Pin 1 (Red/Green), A/C Enable signal from the PCM on either Pin 3 (Blue/Black) or Pin 8 (Blue/Yellow) (not sure which is which here, it's not clear in service info but I do know 1 is A/C request from the Amplifier to the PCM and the other is A/C Enable from the PCM to the A/C Amplifier), and the Evaporator Temp Sensor (Thermistor) (Pins 2 (Yellow/Green) and 10 (White/Blue)) above approx 34F (Temp/Resistance Chart Below)

 

Thanks Crusty. Since the compr clutch was not pulling in (the original problem) it’s probably not likely that moving the temp controls would impact that operation.

my main question is why do I have battery potential at the clutch coil circuit when the the service manual indicated it should read less than 1 volt.

 

Service manual is incorrect about the voltage according to the wiring diagram.

 

Thanks for the reply and confirming what I suspected was a misprint in the pin 9 voltage. It didn’t make sense that it would be such low voltage but I wasn’t sure what was inside the amp such as a voltage dropping resistor. I have the drawings you sent but sincerely appreciate your going to the trouble to send them! There is also a drawing that shows the entire circuit on one page (attached).

Yes, I will have to catch it in the act to troubleshoot it. I have my glove box door off and my meter constantly connected to pin 1 in case the hi lo pressure switch is the issue!

 

Yea intermittents can be a pain to troubleshoot if they won't fail consistently, bad service info on top of it makes for a really bad time.
Good luck and let us know what you find

 

Amen to that! Will post when I have found the problem! Thanks again!

 

Update to an old post. I suspected a bad ac clutch coil so I replaced it with a new clutch assembly. AC kicked in works fine now.

 

Is this a fairly easy fix?? Snaps on the end of the compressor?

 

Not easy because of snap rings inside the clutch assy. connecting it to the compressor. Difficult to get to even with compressor unbolted with refrigerant lines intact.

 

Check the air gap between the plates first... it could be something as simple as that.

 

Air gap was set per mfg recommendations. Clutch coil resistance was low and was blowing 10A fuses.