Okay, I have a 92 Pickup, using a motor from a 2001 Taco.

Other than the A/C compressor, I am using everything A/C-wise from the 3.0. I am using a 3.4 compressor that I swapped the top plate with my 3.0 plate, like UKrunner did his.

On the wiring, I did like vasinvictor posted. I did not use the ACT or AC1 lines at all. The only line I ran was the signal to the A/C clutch to engage it.

I charged it all up. The air at the vent is cold. The gauge readings are proper -- 38 psi on the low side and 379 psi on the high side. The high side line is hot to the touch, and the low side is cold to the touch. There are no leaks anywhere (that I can tell, and I used UV dye). I can't see the sight glass because of where the drier/receiver is installed -- besides, my glass is too dirty to actually see into it anyway. As vasinvictor posted, when the A/C is on, the idle drops (don't have an idle-up function anywhere) and the idle comes back to normal when the compressor is off.

Now, the problem. The A/C compressor doesn't always engage when I hit the A/C button. If it is at idle and the compressor clutch doesn't engage, I notice that it will engage if I rev the engine a little. Once it engages, it will stay engaged until I turn off the A/C. At speed, it's obvious I won't know, but I'm sure sometimes it still doesn't engage because I'll be driving at the temperature at the vents is just ambient temperature. Sometimes if I cycle the A/C button back and forth, it causes the compressor to engage and I do get colder air at the vents.

Is there something amiss? Did I do something wrong or is it supposed to act that way because none of the other wires were hooked up? I haven't checked my thermistor, but just from my knowledge, it doesn't seem the expansion valve is cold enough to freeze yet, so the thermistor shouldn't have shut off the compressor. Not that I won't check it, it just seems to be ruled out as a source for the problem. Any ideas?

And yes, I have thought about wiring a +12V directly to the compressor clutch (with a switch, of course), but that doesn't fix the problem.

Oh, btw, my truck is ref-ed and legal as of June 25, 2012. The first time I went in, it failed for not having a service port on the EVAP and 3 of my OBDII sensors weren't ready. Now it is all good, but my HC's were right on the MAX at 15MPH. At 25MPH, it is well below half of the MAX. This was with brand new aftermarket cats.

I took it to the Florin Road center in Sacramento. They didn't complain about the driver's exhaust drop. The only thing he did say was that the distance from the first flange to the air/fuel sensor, cats, and O2 sensor needs to be spec'ed out. But he didn't fail me for that. The techs there actually commended me for having done a job that looked pretty clean and like stock.

 

There's a knob on the A/C amplifier that changes the low idle compressor shut off. Adjust this one way or another and report back. Several have had this problem.

 

You, sir, are awesome! That was the problem. Fixed the issue.

For future searchers, the 3.0 A/C amplifier has a knob that is labeled "L" and "H". It sets the rev's at which the A/C compressor clutch engages or disengages. On mine, the "L" is for a lower RPM and the "H" is for a higher RPM. If you set it all the way to the "L", the clutch will engage at pretty much any RPM.

As Toyota doesn't list the A/C amplifier as a serviceable unit, they do not document how to adjust this. But this is what I did:

1) Warm the engine to normal operating temperature. You want the idle at its normal idle, not at cold, fast-idle.

2) Leave the engine running and A/C off.
NOTE: If you are having the problem that I had, you should start with the knob at its current location and go to step 7.

3) Turn the knob a tiny bit (5 degrees or so) towards the "L" (clockwise).

4) Turn on the A/C system by hitting the A/C button.

5) Go look at the A/C compressor and see if the clutch is engaged (spinning). (With mine, I can see it from underneath, so I didn't need to open the hood.)

6a) If the clutch is spinning, turn the A/C system off. Go to step 3 and repeat with turning the knob towards the "L" a tiny bit more.
6b) If the clutch is not spinning, continue to step 7. With the knob at its current setting, the A/C compressor is set to disengage (or not engage) at the current RPM.

7) Turn the knob a tiny bit (5 degrees or so) towards the "H" (counter-clockwise).

8) Turn on the A/C system by hitting the A/C button.

9) Go look at the A/C compressor and see if the clutch is engaged (spinning).

10a) If the clutch is spinning, go to step 11.
10b) If the clutch is not spinning, go to step 7 and repeat.

11) Cycle the A/C button by turning it on and off, and check to see the clutch is engaged or disengaged in between each cycle. If it works all the time as expected, then go to step 12. If it is intermittent still, repeat at step 7.

12) Drive it around the block and cycle the A/C button, ensuring your vent air temperature coincides with the A/C system being on or off. If it works properly and your engine doesn't stall when you come to a stop, you are done. If your engine stalls, the knob is set to engage too low of an RPM, meaning the clutch will not disengage the A/C compressor load until your engine's idle cannot sustain itself. Repeat from step 7 to raise the set RPM.

 

Updated with my results.

 

Thanks for updating. If you don't mind, I'd like to link your "how to" in my "A/C thread".

 

No problem at all. It should all be linked so that it's easier to find everything.

 

The gauge readings are proper -- 38 psi on the low side and 379 psi on the high side.
Are you sure thats right???? your high side seems a bit high to me. I've always been told 30/150 at around outside temp of 70.

 

For r134a, your numbers are correct. I used r12. With r12, the high side should be roughly 10x the low side.

 

Any reason you didn't want to convert? I've been running 134 with no problems and not even a full conversion.

 

No particular reason. But I have read that R12 components will not run r134a refrigerant as efficiently as r12 refrigerant. For instance, to get the similar efficiency as an r12 condenser, an r134a condenser needs to be twice the size of an r12 condenser. That's in theory. In practice, there is no real quantifiable way to compare.

I have converted another car to r134a and ran it. But recently, I converted it back to r12 and it is noticeably colder with r12.

 

Interesting, I converted my old 93 accord to 134 and it was ice cold. 92 i converted blows ice cold too. Maybe its just vehicle depending. Hey if you can find R12 then go for it.

 

Yeah, I had two vehicles before (sold by now) that were charged with 134 at a shop with no conversion done and were ice cold. So who knows? Perhaps there were other problems with the system (the ones that weren't cold) too.

I know a guy who still has a good supply or r12 left from his shop and he doesn't charge an arm and a leg for it. I suppose with the r12 replacements like HotShot coming out, the price of r12 dropped back down?