AC Failure Solved

About two weeks ago I got into my Taco and was going to run an errand. It was 105 degrees outside. Turned on the AC and no cold air. I noticed that my AC Buttons light was flashing. The AC had been work fine earlier in the day. Naturally, I was stressed out over this. I had a plan B though (my wife's car). So I could still run errands, in the heat.

My first thought was the 10A fuse. It was good. Then I checked out the MG/CLT Relay. There was continuity on the coil, so it must be good. WRONG. After much waving of arms and knashing of teeth. I rigged up a test jig using a Bosch 12V and an Ohmmeter and some test leads. The MG/CLT relay contacts were not closing. I tested the horn relay on the jig and it worked fine. Put it in place of the MG/CLT relay and still had no cold air and the AC light was still blinking. WTF Over?

So I thought about this a little while and decided to make me a jumper to short the MG/CLT 'contact points' in the relay/fuse box to simulate the MG/CLT relay contact closure. Viola!!! I had cold air,..BUT the AC light was still blinking. There is obviously another issue besides the relay. I took the contact closure simulator out. Now I hooked up a voltmeter to the MG/CLT relay coil to see what it does inside the Relay/Fuse Box. When I started my Taco and turned on the AC, I immediately saw voltage across the coil input on the Relay/Fuse Box for about 2 or 3 seconds then it disappeared. That told me there was a control issue with the AC compressor.

So I started doing some research on the net and in particular Tacoma World. During that process, I took the compressor magnetic clutch apart and cleaned it and verified it was working properly and checked the clearance. It addition, I changed my serpentine belt. No change in symptoms.

Research revealed that the Compressor RPM Sensor signal is combined with the engine RPM signal in the AC Amplifier, where it is 'COMPARED' to each other. If they do not match within certain limits, the AC Amp will drop out the MG/CLT relay, as it is in series with the MG/CLT Relay Coil. In addition, the High Pressure Sensor and the Low Pressure Sensor are also in series with the MG/CLT Relay Coil. Any one of these three will prevent the MG/CLT Relay from picking up, therefore prevent the compressor Magnetic Clutch from activating, thereby creating cold air. Still with me?

OK,..OK,...OK,...Since there was a slight delay before the Compressor was being cutoff, that indicated to me that the problem is with the Speed Sensing Portion of the circuit. So, I tried to find a new AC Compressor Speed Sensor. There was not any available. The Stealership wanted to sell me a whole compressor with clutch and sensor. But I got lucky and found one at a dealership in Florida. About fours days passed and it arrived. I removed the old one and Viola!!! Eureka !!! The AC is working and NO Blinking Lights. !!!!!

If that had not worked,..I would have replaced the AC Amplifier, which is in back of the glove compartment.

I had talked to the Stealership earlier and they indicated that they would have to replace everything to fix my AC. Compressor, Evaporator, Condensor/Dryer and Expansion Valve. Which would have cost me in the neighborhood of $2000.00.

I hope this experience I had will be of help to You out there in Taco Land. At first it was stressful but later it became fun figuring out how the AC System works and finding what was wrong.

Spock Out

 

What’s the part number for that sensor and congrats!

 

Great post what was the cost of the part you replaced?

 

Great job!

 

I replaced the compressor pick up sensor as well and haven't had 1 occurrence of the blinking AC light.

 

Good job!

 

Would you mind sharing the part # you ordered?

 

Great work and great post, thank you for sharing the info bro!

 

88346-04010 ?

 

Compressor Speed Sensor PN = 88346-04010

 

Oh, by the way the Stealership wanted $90 for the MG/CLT Relay. I picked it up at my local AutoZone for $17.00

 

Great write up and way to track down the problem . If you don't mind take some pictures and edit them into the original post to make it the AC repair post of the decade. Subbing for future trouble shooting.

 

Yes, I need to take some pictures and write up a better article that will assist Taco Pilots with fixing their AC's. That may take some time as I am buried right now with 'Honey Do's', but I will try and get it done ASAP.
It really makes you appreciate your AC, when it goes on the blink. We had a 110 degree day last week in OKC.

 

Very impressive work OP!

 

My blower motor in my 2007 was shorting itself because of fine metal shavings that it generated from years of use.

 

motor brushes wear out and the dust from it causes the short

Mine wore out after 6 years or so since I keep it on III all the time for fresh air

 

Thanks for posting the issue and the solution!

 

I need to ask a stupid question...

So If this sensor is bad will the system produce cold air until the the light starts to blink?

I can sit idling for a while and the truck cab isn't cooling but when I rev the engine the AC light begins to blink.

 

Are you still there after all these years? If you are, I have a question... We just replaced the A/C compressor on my 2017 Tacoma and when we try to engage the clutch by jumpering the relay terminals 3 & 5, the Fuse in the cabin, IG1 No2 blows. This fuse controls the blower and temp control on the dash. Any suggestions how to trouble shoot this?

 

Assuming it's the same as the 2nd gen, you could first try directly jumping the clutch with a fuse inline to see if the clutch it's what's causing it to blow.

You can disconnect the single wire coming from the fuse box at the clutch and run a wire straight from the battery with an inline fuse to see if it blows on its own.

Also check that you have the correct rated fuse in there (and don't try to use a higher rated one to "fix" it).