Just installed a new A/C amplifier, A/C Compressor, Receiver/dryer. Pin #7 is the pin that is supposed to send 12V+ to the A/C compressor clutch to engage it. The wire going from Pin #7 behind the dash has been traced and has resistance as well as continuity. Is there something else from maybe a sensor that is causing the amplifier to not send power to the A/C compressor clutch??? I have a back up New A/C Amplifier I will try tomorrow to see if the New one I installed was defective. Also we put a jumper from the Positive post on the battery to the A/C compressor just to test the compressor and it all works. We are just trying to get it to all work normally from the Controls to the A/C Amplifier to the A/C Compressor. Thanks, Picture/diagram below.

 

What do the Manifold gauges read ??

All the criteria needs to meet before the AC amplifier will engage the clutch

Pressure to high or to Low will keep the clutch from getting voltage .

It could be poor connections

Failed sensors

bad switch

something not hooked up

Just what are you working on?

You have to look at the complete AC circuit diagram to figure why things are not working

 

Very correct. There are fail safe's in place to keep the compressor from running dry and without a charge as the r-12 or r-134 lubricates the pump and keeps the pump from staying of and freezing. If you are auto, there is also a temp sensor the kicks a/c off to keep engine from overheating and or transmission from overheating.

 

This should help: http://web.archive.org/web/201204270...ditioning.html

Note that pin 6 is the ignition pulse (the compressor won't engage with the engine not running). It's just a pulse, so it is possible that your voltmeter would only show 0v at idle. You need that pulse, as well as the appropriate signal from the thermistor and the pressure switch.

 

I see so many try and test things on a new install without charging the system.

Then wonder why it does not turn the dry compressor on

 

Everything was hooked up and charged after the new parts were installed before we tested anything. My buddy works at a shop that has the A/C machine that Evacuated the system for 30 mins then charged the system precisely afterwards. Then when the A/C compressor would not come on with the normal controls on the dash that is when we used alligator clips to power on the A/C compressor which worked and blew cold air into the cab. That is when he started wire chasing VIA ALLDATA and continuity/ resistance checks from the A/C compressor to the A/C amplifier.
I cannot remember what the gauges were reading but honestly my buddy said, "They were within spec for a truck that was idling." the high side was a little high because it was idling he said and the condenser wasn't getting the normal flow so he said that was ok.

 

As I said, pin 6 is the ignition pulse, and your test shows 0v. According to the manual, http://web.archive.org/web/201102052...ng/22airco.pdf you should get 10-14v with the engine running.

Also, pin 8 is ground, and your measurements show (I think) 10v. That obviously is incorrect; I'd start there.

But, pin 4 goes to the A/C switch, and your notes show NO connection there. The manual I've linked is for a '93, but this sort of wiring doesn't change much with the years. Alas, you may the one to discover that it does.

Good luck!

 

Thank you for the luck, that is where we shall start looking into things first. I will keep this updated until fixed properly.

 

Forgot to add this pic with some more info of the conditions being produced.



My buddy says we may have a crossed wire and a possibly a bad thermistor

 

Ya think? Here's the specs: http://web.archive.org/web/201102052...20thermist.pdf

Careful, though. On most digital multimeters, "0L" (which is arguably short for over-load?) means the "resistance is too high" ... for this range! In automotive, we're usually just looking for continuity, 0L on any range means "open," and that's good enough. The thermistor runs from about 1.5k ohms (room temp) to 5k ohms (really cold). If you had your multimeter set to the 200 ohm range (our favorite $7 multimeter has that range), then a within-spec 1.5k ohms would read 0L.

So re-do your thermistor test, just to be sure.

 

some of these also had a dial for rpm kick on/ kick off. On a few 3.4 swaps I've done there was a need to turn the dial to the lowest setting.