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Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14422
Experience:  Toyota Master Diagnostic
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The A/C light blinks on my 2008 Toyota Tundra. It is the

Customer Question

The A/C light blinks on my 2008 Toyota Tundra.
JA: Just to clarify, can you tell me which light it is? And does it blink first, then stay on steady?
Customer: It is the light on the AC button (green light). When I push the AC button to turn on the ac, it will be solid green a few seconds before blinking, at which point the AC quits operating. This also affects the defrost setting
JA: Are you fixing your Tundra yourself? What have you tried so far?
Customer: So far I replaced the relay. Yesterday I had a mechanic look at it and it was low on 134, so they evacuated the system and recharged it plus changed the Schrader valves. I'm trying to diagnose myself...their $335 fix didn't work.
JA: Got it. Anything else you want the Toyota Mechanic to know before I set up your one-on-one?
Customer: I think that is all. It did start the moment I pulled it out of the bay at the Toyota dealer after a "used car" inspection. Coincidence perhaps.
Submitted: 10 months ago.
Category: Toyota
Expert:  Skyvisions replied 10 months ago.

Is the compressor locked up? What are the pressure readings on the low and high side at idle and at 3K RPM?

Customer: replied 10 months ago.
I'm sorry, I do not know the pressure readings. I know a local mechanic added 134 to it yesterday and replaced shrader valves. The compressor turns when the light is solid green....this is an intermittent problem. More often than not though.
Expert:  Skyvisions replied 10 months ago.

First of all little information on how the system works. When the AC comes on either by being in the defroster mode or one turning the air-conditioning system itself on the magnetic clutch relay energizes sending 12 V to the winding of the magnetic clutch. Once the compressor starts to spin there is a rotational sensor built into the air conditioning compressor. That rotational speed sensor has to match the engine RPM if it does not the AC amplifier will shut power off to the magnetic clutch relay. There are only a few things that will cause this the first one is the relay that you said you've already replaced that. I normally tell people to swap it out with the horn relay and see if the problem goes away a lot of aftermarket relays don't work well. The only other option is the compressor itself is starting to lock up or the pressures are too high so that it causes the speed sensor to detect slower rotation of the compressor compared to the engine RPM so the AC amplifier shuts the system off. If there's any belt slippage it will cause the same thing. The magnetic clutch itself is slipping it will cause the same thing. It is one of those three or four areas that have to be checked. It's very rare to see the actual speed sensor itself fail.

Customer: replied 10 months ago.
Thank you for that information. After work, I will swap the relay to double check, since I did use an after market. I will replace the serpentine belt (age unknown). From there, I will start working the list from cheapest to most expensive.
Expert:  Skyvisions replied 10 months ago.

Ok see how hard the front of the compressor is to turn with the engine off. Should turn by hand with some resistance.

Customer: replied 10 months ago.
The mechanic I had assess the system yesterday stated that at idle and the compressor on the high side was 150 and the low was 20. At idle with the compressor off, the high side was 150 and the low was 40.
Expert:  Skyvisions replied 10 months ago.

If his gauges are correct and at idle you have 150 on the high side in 20 on the low side that would indicate that the air-conditioning is under charged. A normal operating system at an average of 80°F ambient temperature will put you at about 220 on the high side and about 32 give or take five on the low side. With the compressor off after about 10 minutes both sides should equalize and be the same if they're not this would indicate an issue with the compressor. He probably didn't wait long enough when he looked at the pressure readings.