Maybe Unique A/C Problem?

I've searched the forums pretty good and cannot find another post with these similar symptoms. Most AC problems seem to come with a blinking AC button light or a noisy compressor and I have neither.

The clutch on my A/C compressor engages intermittently, about every 3 or 4 secs at idle. The result is a barely cool truck at max cool settings.

I've replaced both the magnetic clutch relay and the A/C relay in the fuse box under the hood.

I've recharged the system. It was slightly low.

Blower motor and vent switches work fine at all settings.

AC indicator light stays on, does not blink.

No funny noises from compressor, pulley turns smooth.

Unrelated to the AC diagnosis, I replaced the serpentine belt about 1k mi ago.

The AC does work better at higher rpms. Not sure if its because the compressor is engaged the entire time or if its just turning faster for the periods that it is engaged.

What are some other things I can check?

Thanks!

 

Sounds like it is over pressured. I went through this last week on my wifes car. The fact that it cycles on so much leads me to believe that there is too much pressure. Just my experience.

 

Thanks for the reply!

How can I bleed off some pressure? I do have the hose with the gauge and fitting that pierces the cans of refrigerant. If I attach this to the low pressure port without the refrigerant can and pull the trigger will it vent out of that end or is there a one way check valve on these things?

 

Check the pressure with the gauge on the can. If it is too much, use a nail or small screwdriver on the low pressure side to bleed some off. Be careful not to freeze your fingers though.

 

Did you use a manifold gauge set that attaches to both the high and low pressure sides or one of the AC kits that only have a low pressure hose? There could be several issues that cause poor cooling such as a partial blockage, etc... You may not be able to tell with just a low pressure gauge. Hopefully it's just overcharged and pulling a little out will fix it.

 

I had a similar problem, my AC unit would randomly just stop working while I'm driving. The dealer changed out a relay switch in my tacoma 2010. It was causing my AC line to freeze up completely so blower/clutch wouldn't turn on. Easy way to check is when it's happening, open your hood and look at the AC line, you'll start seeing frost build up on the line. Part number is TOY

$26 90987-02028 Toyota Genuine Magnet Clutch Relay

90987-02028. Maybe that might be your problem. My dealer was running into a couple trucks with this issue.

 

Thanks much for the info! I'll check the system pressure, bleed off if necessary, and report back

vssman, I used a single gauge on the low pressure side.

TacomaToday; I replaced that relay yesterday Found it at NAPA...expensive little bugger at $27. Its for the magnetic clutch. The other relay is in a smaller box attached to the main fuse box under the hood. It has a single relay for A/C in it. Replaced that one too.

 

If it works at higher rpms 9/10 times you have a bad compressor

 

Ok. The can should tell you that the pressure is correct when the compressor is on. Make sure that is the reading you're using and not when it's not cycling. You can overfill if measured when the compressor is off.

 

If it's cycling that fast, it's either way overcharged (covered above), very undercharged (low pressure drops fast when compressor kicks on which opens low side switch, but high pressure doesn't go up much) or possibly there's a plugged expansion valve (expansion valve is in evaporator).
how do you know it's undercharged (slightly low) in op? with a full gauge set?

 

what are your pressures reading at idle with max ac on

 

It was reading around 50psi initially. After bleeding some off its reading just over 40psi. Compressor was running constantly in the parking lot after I bled off pressure. Going to run it around tomorrow and see how it does.

Hopefully this fixes it. This experience has allowed me to learn way more about ACs than I ever wanted to haha. Seemingly complicated stuff.

 

This

 

Too much pressure then. I bet it will start working fine now

 

Watch it and make sure compressor is cycling in normal usage. If it's running full time, esp in moderate weather, there's still something not quite right. In humid weather should show a pretty good drip from the condensate tube.

 

Seems to be running fine and blowing nice and cold! This was a thankfully easy fix

 

Nice! Glad to hear it.

 

I have a 2012 Tacoma, I'm still under my warrenty I also bought the extended warranty. I'm trying to get the dealer to fix a similar problem with my A/C. It doesn't want to cool if I'm sitting and the truck is running. They replaced the clutch recently. What else can make the A/C blow hot air or stop cooling if the truck sits at an idel for a while? They want to reproduce the problem before they fix it, but it's intermittent.

 

Low charge or over charge is the most common cause. Have they checked the pressures?

 

They said they checked the entire system when they replaced the clutch. I'm not sure what they did, I'm not a DIY mechanic, so I don't know much about this kind of stuff. I have always had/paid somebody else do the work for me.