Automotive Air Conditioning Information Forum (Archives)

Jag987 on Fri July 18, 2014 4:16 PM

Year: 1993
Make: Toyota
Model: Pickup
Engine Size: 2.4
Refrigerant Type: R134a converted
Ambient Temp: 80
Pressure Low: 37
Pressure High: 210

The short version- With the truck idling, the compressor will not engage, with the engine a few hundred rpm's above idle, everything works great.

The truck came to me with a very poor cooling issue of a very low charge and little air flow coming out the vents. I found the fins on the evaporator core were plugged up with dirt and other debris. I was unable to clean it out without damaging the fins, so it was replaced along with the expansion valve and drier. I replaced the O-ring on the other joint that was leaking, the fitting was only about finger tight. It held vacuum and everything went great charging. The system calls for 29 ounces of R12, it has been previously converted and I settled with about 25 ounces of R134a in it. Once the engine was revved up to about 1500 rpm's then came back down to an idle, the compressor disengaged. The High side pressure had reached just over 300 so I though it could have been the HPCO, but it never came back on. If I rev the engine even a few hundred rpm's above idle, the compressor with come back on. I have tried adding more and taking out refrigerant, and made sure all electrical connections were done up and making good connections. It was working at idle while I was charging, but not after the rpm's were raised for the first time after charging.

Any ideas? I think my customer will be happy, but I am not.



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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

mk378 on Fri July 18, 2014 5:09 PM

The computer is usually programmed to drop out the compressor if the idle rpm is too slow. Is the idle rpm at specification?

Jag987 on Fri July 18, 2014 6:39 PM

I had that thought, spec is 750, right now it is about 900. Just discovered the fan clutch is bad.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Jag987 on Sat July 19, 2014 12:42 AM

But a bad fan clutch would not explain why it will not come on at an idle.


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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

wptski on Sat July 19, 2014 8:58 AM

Something in the HVAC logic in the PCM and/or HVAC module.

Jag987 on Sat July 19, 2014 1:31 PM

Quote
Originally posted by: wptski
Something in the HVAC logic in the PCM and/or HVAC module.

Genius! I had to do some reading on Toyota forums but I learned more about the control module mounted to the evap box. I saw the knob on it that said "rpm" with a "+ and -" on it. I just barely turned it down, and the compressor came on. Thanks for your help everyone.

Stay cool out there!
Jag

-------------------------
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

alan73 on Sat July 19, 2014 2:06 PM

is the a/c amplifier adjustable? not sure what year they quit making the amplifiers adjustable but you might check and see if there is an adjustment knob on this year model.
there is a lot of Toyota based forums like Toyota nation or yotatech that might be of more help.

wptski on Sat July 19, 2014 2:34 PM

Quote
Originally posted by: Jag987
Quote

Genius! I had to do some reading on Toyota forums but I learned more about the control module mounted to the evap box. I saw the knob on it that said "rpm" with a "+ and -" on it. I just barely turned it down, and the compressor came on. Thanks for your help everyone.



Stay cool out there!

Jag
Come to think of it, I had a 1979 Toyota 4x4 mini pickup. Maybe because it was four banger, the A/C cut off at idle. Luckily it was a manual shift so if you got stuck in traffic, you could easily raise the idle to get it to kick on unless you wanted to sweat.

Number4 on Fri August 01, 2014 9:03 AM

Quote
Originally posted by: Jag987
But a bad fan clutch would not explain why it will not come on at an idle.

If the fan clutch was bad and the fan wasn't rotating sufficiently, wouldn't this cause the refrigerant to build up too much pressure and then the system would shut down?
But when moving, the air across the condenser could be enough to lower the pressure and allow the AC to function again.

Jag987 on Fri August 01, 2014 12:29 PM

Yes you are right about the fan and building up pressure, but it was not shutting off due to high pressure. When I was replacing the evaporator, I must have bumped the rpm control knob on the ac control module/amplifier. As soon as I turned it up a little, everything was good. The fan clutch does still need to be replaced, but it was not in their budget at the time.

-------------------------
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!