AC Diagnostic Help

Here is the story so far.

My AC does not work. Before any questions about when it stopped or the history of the truck I do not know. The truck is "new" to me and the AC has never worked.

What I did:

• Took it to a mechanic for a leak test and was explained the system had no refrigerant.
• Pulled a vacuum (-28) which it held for over an hour. I actually did this twice. Number never changed.
• Tried to add refrigerant... low side pressure would stop at 50psi and compressor would only click on momentarily.
• Every time AC button was engaged, compressor would kick on for a second or two, then AC light would flash. Then compressor would turn off.
• System would take on hardly any refrigerant (basically none).

I cried uncle... and took it to the mechanic.

What they did:

• Evacuated the system and did a vacuum test (passed). Was low on refrigerant (understandable as I could not get enough in)
• Charged system with refrigerant... compressor would not kick on... same flashing AC light problem.
• They jumped the relay (part 98987-02028) and got the compressor to come on.
• Still no cold air. AC light would start to flash.

It has been suggested that the AC amplifier and relay are bad and that both should be replaced.

Any opinions, theories... alternate tests or ideas?

Or should I just keep the windows rolled down and call it good...

 

The Ac led flashes when the engine speed and the compressor speed do not agree.

My guess.

Defective AC compressor clutch.
Defective compressor rotation sensor or wiring.
Defective r134a pressure switch.
Defective compressor.

Prints: http://www.customtacos.com/tech.old...toyewd/06toypdf/ewd/2006/tacoma/h/em01d46.pdf

 

So... would better course of action be to just get a new compressor and also swap out the pressure switch?

Sounds like you are saying it's unlikely to be a relay / amplifier issue...

 

I would suggest further troubleshooting using the the sheet I linked above rather than throwing parts and money at it.

 

I suspect that if there was an item that would deter the PO from repairing the AC due to it's high cost, that item would be a faulty compressor. I concur with JimmyH regarding the troubleshooting route.

 

did you put two jumpers in place of the relay or 1 .1 jumper made my compressor spin but not cold , added a second and got cold and no blinking light. That told me the Amp was not telling the clutch to spin the compressor. Speed sensor was good , 134a level was good pressure switch was good. Replaced the amp and all was well.

 

I'm not really great with A/C, but I know enough to be dangerous... and usually enough to know when I'm being dangerous.

Did the shop eventually get a correct charge in it? Do you know what pressures they were seeing either way?

Getting barely any in and having 50psi on the low side sounds like a clog somewhere, from my memory. Haven't had to do it with just gauges in a long time, but I seem to remember seeing around 100psi on an equalized system. If the shop couldn't get it charged either, did you have a gauge on the high side too?

 

The mechanic jumped the relay... I am not exactly sure how he did it. This pic might help identify what he did. He admitted it was a odd way to test it but felt the relay was shot already (not sure if I believe him... but it is what it is). To me it looks like it was only jumped in one spot (the chipped portion).

According to him this "jump" made the compressor click on. I assume that meant the clutch engaged.

In your case... what was the difference between the compressor coming on... and the compressor coming on and blowing cold? I mean... doesn't the compressor clutch engage and then work, or the clutch does not engage and doesn't work at all?

 

It's my understanding they were able to get the correct volume in... but I did not get information on the pressures they were seeing.

I had a gauge on the high side when I did it myself but I honestly don't recall the pressure. The system just stopped taking on freon no matter what I tried so it went to the shop.

 

I agree with you both. I would prefer to identify and solve the problem then just start replacing parts. But I am not really sure how to test the pressure switch or compressor rotation sensor.

I would assume the pressure switch would need to be removed to be tested.... and I assume that would require the freon to be removed first, system empty.

Honestly the pressure switch and relay and pretty cheap. The amplifier seems to be under $100 so still not terrible. But I will admit getting a compressor and the rest I would definitely prefer not to just "guess" at.

This is the first time I have taken a vehicle to a mechanic. I am generally pretty capable turning wrenches myself from engine swaps to all sorts or modifications. But I will admit electrical understanding and troubleshooting is a weak point for me, and AC systems even more so.

 

Definitely this here

Here is the areas you need to look at although I've not done many A/C repairs, but if those with a similar situation, i had to replace the pressure switch or clutch switch with your symptoms.

TEST THEM FIRST, though. I can't reiterate enough to diagnose before you drop hundreds on parts and labor you don't need.

 

I removed the relay and put jumpers in the socket. Use the search tool and you will find out how to test each component. Process of elimination . if all test were good and the amp has a good ground it may be a bad amp as I had . Their are many things that will make the light blink and no AC . All of those sensors and switches report back to the amp or get a signal from it.

 

We would see flashing A/C lights on Lexus GX470's at work. There was an updated relay TSB.

 

Why is your relay melted?

 

Not melted... that was how the mechanic "jumped" the relay to confirm the relay was bad. At least, that is the story I got.

 

Dude! You need a new mechanic. That one is an idiot!

 

Well... this is why I try to never take my truck to a mechanic

 

More likely the "mechanic" used a pair of pliers to remove the relay and cracked/broke the relay housing in the process.

 

OK... here is what I have tried so far still with no luck..

Replaced the "bad" relay
Tested pin 2 and 5 at the relay, both have 12V with engine on (seems to be correct)
Ran a wire with a switch to get 12V to the AC clutch, clutch will engage (seems to mean clutch works)
12V at pin #12 (IG+) on the amplifier with the key on (seems to be correct)

AC light still flashes, compressor only comes on momentarily but draws in about a 3/4 can of R134. At this point, low pressure is 100 and high pressure is 95. Then no more coolant, light flashes, can only get compressor to turn on with AC button for a brief moment then AC light flashes.

Then I...

Bypassed pressure switch with a jumper between wire harness pins (per FSM pressure switch test instruction)
Replaced the pressure switch
"Forced" the AC clutch to run with bypass 12V switch with engine running
Replaced amplifier (with #88650-04030)

Still nothing. Flashing AC light, no pressure change, won't take more R134.

What should I check next? Frustrated beyond belief...