AC Compressor Stopped Engaging

[shultzee13]

No the rear AC is not blowing cold either. Same as front. But it did work like front until AC compressor stopped engaging last Saturday.

Yes I replaced the compressor, dryer and o tube when I installed new compressor. I vac'd it down and did refill.

When I hook up test light to battery positive and touch compressor wire harness from back of compressor - the AC clutch will engage and I get cold air.

AC Relay is brand new. All fuses good.

Can a bad condenser cause this? I only ask this question because I go back to my original problem that was it not blowing cold at stop lights - idle.
Can the condenser completely fail and cause compressor not to engage?

I can't shoot dye into system to look for leak because AC won't engage.

Should I VAC it all the way down, and start from scratch? I guess I could take everything apart and look at the o tube.

Just not sure what the smartest approach would be money wise.

I do know the condenser has got some miles on it for sure. I would go ahead and replace the condenser if I knew a failed unit could cause the AC compressor to not come on.

[71403]

When I hook up test light to battery positive and touch compressor wire harness from back of compressor - the AC clutch will engage and I get cold air.

Need to specify which wire(s) you're talking about. Picture would help.

Just not sure what the smartest approach would be money wise.

Trip to a shop with diagrams and a real scan tool will be cheaper than randomly throwing parts at it.

[shultzee13]

The round connector on the back of the compressor that connects to the ac cycle switch

[shultzee13]

The round pressure switch on the back of the compressor. Put a test light to that and battery positive compressor clutch engages

[JohnHere]

Perhaps I wasn't sufficiently clear in my earlier post.

Using only a low-pressure gauge on a can with a hose and gauge--also known as a Death Kit--is not a credible way to diagnose and charge a system. You also didn't say whether the pressures you observed are static or dynamic, what the ambient temperature is, how you evacuated the system, and how you measured-in the charge. I hope that you didn't introduce any sealer into the system.

Regardless, the gauges attached to these cans are known to be unreliable at best. So the pressures you're seeing on the gauge might be (and probably are) far off. Because of that, I routinely disregard them. Apparently, you don't know what the high-side pressure is, making whatever readings you get with the unreliable low-side gauge even more questionable. At this point, I don't think you know how much refrigerant is in the system despite what the Death Kit gauge reads. In any case, you can't determine the proper charge by pressures alone.

To diagnose this, I would ensure that the system has the correct charge by using the proper equipment. After recovering and weighing the refrigerant (and possibly finding it low), I would recharge it to spec. If the compressor now runs normally, great. Use the A/C for a few days and then check for leaks as I described earlier.

You said that the compressor is brand new and eight months old. That's not exactly brand new anymore. There could now be a problem with the compressor as well. But without a correct charge and knowing both high and low pressures, we can't judge for sure whether it's pumping efficiently.

You mentioned that the condenser has some miles on it. Among other things, the condenser is the main system filter and should have been replaced along with the compressor. Should you replace it now? Your call, but it might be a good idea, especially if it's the 20-year-old original. Airflow across the condenser, or lack thereof, can also cause problems with pressures and cooling performance...something else you might want to look into.

Could it be an electrical issue with the ECM and/or AC amplifier? Certainly. But I would first eliminate the mechanical parts of the system and the amount of the charge as the source of the problem, and then go on from there if necessary.

I also agree with 71403.

Trip to a shop with diagrams and a real scan tool will be cheaper than randomly throwing parts at it.

(This.)

[71403]

The round pressure switch on the back of the compressor. Put a test light to that and battery positive compressor clutch engages

Ah, ok, so exactly what a shop told you a few posts ago? Then you need a wiring diagram and figure out what's wrong,

Can buy short term access from Mitchell or Alldata.

[shultzee13]

95 PSI on low side - 2:30 o clock on gauges
100 PSI on high side - 8:30 o clock on gauges

The AC was turned on for these readings.