AC Issue - Compressor sometimes will not cycle. Cause?

Guys,

2012 Base Tacoma, I've owned it 3-4 years and no AC issues until now.

I drove it about 50 miles Saturday. As it was about 80, I turned on the AC at the start of the trip, but it did not blow cold air. The AC light was on solid on the dash. I tried punching it several times off and on. The light would go off and on but no cold air blowing.

About 20 miles in, the air got cold for about 30 seconds....so the compressor definitely ran. Then it went back warm again. About 5 miles after that, cold air started blowing again and the a/c worked normally for the rest of the trip.

I put my gauges on it when I got home. I show about 45 PSI on both sides with the truck off. When I started the truck and turned on the a/c, the compressor kicked on normally and ran for about 45 seconds before cycling. At this point the low side had dropped to 25 psi and the high side was around 180 PSI.

I'm viewing this as a little low on freon since compressor is pulling the freon down enough to kick out on low pressure and cycle on and off.

However, with the freon checking 45 PSI with the engine off....I don't think I've found the real problem here.

When the compresssor does run, the ac blows cold. I mean, with just a regular cab, you have to turn control knob off max or it will be uncomfortably cold.

I'm thinking some chance it's a failing a/c clutch relay....but I've never run into one that "sort of worked" before. Always either worked or it didn't.

Anyone run into this before?

 

Try to add some refrigerent or it could be the expansion valve.

 

Those number are close to normal. Around 30 (+/- 5) psi in low side. and 210 psi (+/- 10) on High side.
The high side might be a bit low according to my data. (but maybe just fine)
I am NOT an AC guy. @Dm93 is my go to AC guy here on TW.

 

Just replaced the a/c clutch on mine. Considering it’s been on for 15 years, I’m good with that.

 

Trying to fix AC issues blindly, only makes it worse.
I wouldn't add anything, or replace anything, until I KNEW what the issue was.

Paying someone to do A/C and Transmission work is money well spent, if you don't know what you are doing.
I am one of the "Don't know what I'm doing" people. I make my problem, someone else's problem.
Then I take it back to THEM when it breaks.

 

If the A/C light isn't flashing when this happens it isn't the clutch or circuit for the clutch.

What is the ambient temperature? Those static pressures seem low, running pressures seem pretty close depending on ambient temp.

 

On the trip, it was about 80 degrees. When I was diagnosing with gauges, it had dropped a bit....maybe 78 degrees.

So....just to verify....if the ac light doesn't flash that rules out both the compressor clutch and the compressor clutch relay?

If that's right, I'm out of ideas. The AC light was definitely ON for 20 miles with no cold air being produced. Then it just got cold all of the sudden for 30 seconds, got warm again and 5 minutes later got cold and stayed cold for the next 30 minutes (rest of the trip).

What about a sticky pressure switch? Is that a thing?

 

The static (system off) pressures are very low then, typically the static pressure in psi should be at or above ambient temp in degrees F on a properly charged system.

Yes because the A/C Amplifier continously monitors the compressor lock sensor circuit when it commands the MG CLT relay on and will lock out the compressor & flash the A/C light if it doesn't detect an RPM signal from the compressor.

Certainly possible, kinda need gauges on it when it acts up to see what the pressures are doing.

 

Possible final follow up for now.

I put gauges on it last night and verified the pressures high and low were low by 10 PSI / 30 PSI. Added R134A until pressures were in spec and all seems fine. Compressor is no longer bumping into the low pressure cut off and instead clutch remains engaged (windows open, AC on Max recirculate, 82 degrees ambient).

The only thing I can think to explain what happened over the weekend was (MAYBE?) it was cool enough out that the freon pressure was too low to allow the compressor to kick in, and then, as I drove and the engine bay warmed up, the freon pressure increased and caused the binary switch to close, thereby engaging the compressor.

But I still don't think the freon was that low. I was checking it at 45 PSI with the engine off, which should have at least allowed the compressor to cycle and create some cool air....but it didn't. Flip side, that was after I drove it 30 miles home and left it parked with the hood closed....so....heat.

I will post back if it fails again. Last night after charging to spec, it was running fine.