Air Conditioning Weirdness

I had the frame replaced on my 2009 4.0L Automatic Tacoma Access Cab in 2018 at 78K miles. I believe that part of the procedure involves draining and recharging the AC system. In 2022 at 107K miles, the system seemed to have trouble blowing cool air, so I had the system checked by a local independent shop. They pulled a vacuum on the system, and recharged it. All seemed good for 7K miles. In 2023, at 114K miles, I ran a quick errand and when I left the store and re-started the truck the serp. belt let out a scream as it was pulled over the A/C compressor that was not turning. I shut the A/C off, and everything was normal. When I turned it back on the banshee returned, leading me to the conclusion that the compressor had seized.

I tried to address this by buying all of the tools and components (Denso compressor, Denso condenser, valve core, R134a etc. etc. $950 worth of components, $200 in new tools) to rebuild the system. I got the system rebuilt and working, but the compressor was making weird noises. It turns out that Amazon had shipped me a compressor that sombody else had already returned! Arrgh - I then went to a local shop that specializes in Auto AC, and had them replace the compressor, and recharge the system for an additional $1350.


All was great until this week (5-18-2025). At 136K miles, I was driving home from my work, and the cab seemed to be getting stuffy, so I turned the knob from cool to MAX AC. The AC and Recirc. lights came on (no flashing) but there was no change in the air temp. I kept playing with it during my next three 50 mile commutes, but no joy. I would turn the AC knob to MAX AC and the temp of the air from the vents was the same.

So today I went to another independent shop to have them look the system over. $78 later, they tell me that all is good, and the system is fine. When I picked up the truck I tried the AC, and YES, it is working fine...

Can any of you AC experts suggest or guess what's going on?!?

TLDR: I turned on the air conditioning the other day, and did not get cool air out of the system. Today, I had the AC system checked, and no fault found - It's working fine. What's up with that?

 

Magnetic AC Clutch?

 

2014 AC V6 6spd MT, ~84K miles.

I've had this happen twice now, in 2 different years.

Conditions: first time activating the AC after a long winter season with no use.
Symptoms: AC light turns on solid (no blinking), blower blows air, but no cooling happens at all.

After cycling the AC & blower switch on and off maybe 20 times over a space of 25 minutes, still no joy.

Wait a few days or a week, and next time I try the AC --- voila, it works fine, no issues.

Actions taken: None, no testing, recharging, or attempts to replace any AC parts.


I tried googling around a bit on this and haven't found anything conclusive so far. The closest rumor-explanation I've seen so far is that after a long period with no use, refrigerant collects or settles in either the evaporator or the condenser (?? not sure which) and refuses to move & circulate when the AC compressor spins. Like maybe some kind of fluid air-lock sort of thing? A vaccuum bubble in the system somewhere?

Another theory I've heard is that after a season with no use, the AC clutch solenoid might get sticky & not engage, but after attempting to cycle it on/off X number of times it finally gets "unstuck" and manages to self-lubricate enough to make it through another full warm season.

I don't understand the cause. All I know is that the problem has so far happened only twice, in 2 different years, at the start of the summer season, the first time I try to activate AC. For the rest of the summer the AC keeps working fine.

 

THIS may be the situation!

On Saturday, I just returned from being away for 5 weeks (Florida, a transatlantic cruise, then 2 weeks in Italy). I re-installed the battery on Sunday, and drove the truck on Monday and Tuesday. Monday it was warm-ish, and when the first sign of trouble was noted.

Thanks, but the mystery continues.

 

If the mag clutch wasn't engaging the a/c light should be flashing. It flashes when "compressor speed doesn't match engine speed" (ie, broken belt, bad clutch, etc)

Maybe a blend door issue? Maybe some debris blocking expansion valve?

If it was in my bay first thing I'd be doing is verifying correct amount of refrigerant is in it

@Dm93

 

I don't recall the exact relay, but on my daughter's Corolla, her AC quit working but had a good charge. It turned out to be a relay under the hood. I could imagine that relay getting 'flakey' before it quits working. Find that relay (on her Corolla, it was under the hood in the main fuse box) and give it a tap or unplug it and tap it a little, then reinstall the next time it stops working.
If that 'fixes' the problem, I'd replace that relay. They're pretty cheap.

 

Yep, intermittent clutch relays are common on Honda vehicles

Still, on a toyota, I'm pretty sure if the a/c button (request) is on and it doesn't see the mag clutch spinning (through the compressor lock sensor) the light should be flashing. Pretty sure that includes a faulty mag clutch relay. But there's also a a/c amplifier module that I dont really know much about. I think the a/c button tells the amplifier to engage the mag clutch relay, and then the amplifier watches the sine wave from the lock sensor to make sure everything is happy..

Dm should be along sooner or later, he knows his stuff..

 

Correct, if the A/C Amplifier commands the MG CLT Relay on but doesn't detect the correct speed signal from the Lock Sensor it will turn the relay off and flash the A/C light so a faulty relay or clutch would result in a flashing A/C light.

There's multiple inputs to the A/C Amplifier to enable the A/C, any one that is not correct would prevent A/C operation:

Engine Speed (Tach) Signal from the ECM in range
A/C Enable signal from the ECM
Dual Pressure Switch closed
Evaporator Thermister in range
Engine Coolant Temp signal from the ECM in range
Ambient Temp Sensor in range (09+)
A/C Request from the A/C Switch or one of the blend door servos

 

But as I and @GilbertOz observed, the light on the AC switch comes on SOLID; no blinking/flashing.

I did a quick test during the failure with the engine idling. I could hear the magnetic clutch engage ("click") when I pressed the AC switch. The ambient temp was in the mid to upper 60º's F. This leads me to believe that the AC relay, and the magnetic clutch are working as they should.

The only symptom was no cold air.