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Old 07-10-2017, 06:14 AM   #1
sceh
 
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A/C advice please

My A/C doesn't work. When I press the A/C button there used to be a drop in revs because the mechanically driven pump was now engaged - presumably through an electrically engaged clutch?
Since my wonderful Haynes manual avoids talking about anything useful (like this or the auto box...), how can I test this? In other words, do you know which wires connect to the clutch so I can see if there is a voltage?
Obviously the voltage could be there IF the computer says there should be and IF the pressure is low then it might say no. If I know the wires, I can force it to at least see if the pump is OK before I add gas.

thanks for any help
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Old 07-10-2017, 10:38 AM   #2
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Youre right the clutch is electrically activated. You should be able to find the wires going to the clutch and check for voltage. Also, you should check the fuse. I think you will find voltage at the clutch and the fuse is good. If not...theres the problem.


Beyond that I cant help! Good luck and be sure to tell us what the problem was!
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Old 07-10-2017, 11:14 AM   #3
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There is a pressure sensor switch the will disable the compressor if your coolant charge is low. You need to check the pressure in your system.

The pressure sensor itself could be bad, but not likely.

Lastly, you could be experiencing what has happened to my compressor. The internals of the compressor seized and the clutch is not activating. Compressor replacement would be in order.

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Old 07-10-2017, 11:59 AM   #4
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SO, no voltage at the compressor with the engine running and A/C switch on or off. Fuses OK too.
I will try to find and bypass the pressure switch to see if this changes.
There is no mention of the A/C in the wiring diagrams in the Haynes manual - pity
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Old 07-11-2017, 04:19 AM   #5
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TIred shorting out the pressure sensor - there are four wires so I tried all combinations but the pump did not engage. I disconnected the only wires to the pump (2) and put a battery across them with the engine running - nothing happened. The resistance across them is pretty low - less than 0.3 ohms so not quite a short.
So, looks like the clutch is jammed or broken. Broken is less likely than jammed so later I will try a Barnsley screwdriver when the engine is running.
If that doesn't work I might drain the system and remove the pump to see if I can fix it.
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Old 07-11-2017, 04:45 AM   #6
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This the best video I have ever seen on Youtube - clear and well explained and already tells you that repölacing the pump or removing the pump is not needed.

https://www.youtube.com/watch?v=RFC5jMhUm4s
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Old 07-11-2017, 09:23 AM   #7
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The plot thickens. The internal part of the pulley should not turn normally until the clutch is engaged. So, the normal, non AC, case is that the pulley runs freely and only turns the pump when the clutch engages - hence the drop in revs.

Can someone confirm this on their Yaris?

On mine, the internal part turns all the time, implying that the clutch is jammed in the engaged position. If this is the case, I need to lever it out or lubricate it or change it.
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Old 07-11-2017, 09:55 AM   #8
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Our compressors are not built like the one in the video. On ours what you see spinning and think is the clutch is not the clutch. That piece is always spinning engaged or not.

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Old 07-11-2017, 10:13 AM   #9
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Excellent - thanks for that!
So, the clutch is inside the pulley and doesn't move visibly when engaged? I suppose that it can't be heard either due to the engine noise?

So my tests of shorting out the pressure valve are a bit moot.

However, applying a voltage when it is not moving with the engine off yields no noise so can I assume it is duff or jammed?

To get at it I assume I undo the single bolt in the middle and pull?
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Old 07-11-2017, 11:24 AM   #10
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So, here is the FOUR-pin connector on the high pressure A/C line on the top of the engine. I thought it only had three terminals. Does anyone have the pinout for this?

thanks
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Old 07-12-2017, 10:13 AM   #11
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Give me 30min. I will have the complete wiring diagram and pinout for your connector

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Old 07-12-2017, 11:00 AM   #12
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Pressure switch

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Old 07-12-2017, 11:00 AM   #13
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Close up

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Old 07-12-2017, 11:01 AM   #14
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A/c amp

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Old 07-12-2017, 11:02 AM   #15
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A/C compressor

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Old 07-12-2017, 11:07 AM   #16
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So I show it to be a 3 wire on all north American cars from 2006 to 2012. So our wiring is diferent than yours. So not sure if this will help you for the pressure switch. Let's back up. Go to the A/C compressor. White and black wire is ground. Verify you have ground there. If that's good supply 12v to the light green wire you should get clutch engagement. If not the compressor clutch is bad. If ypu do get clutch engagement your high pressure side should get got and low sign should get cold. Check it this way and get back to me.

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Old 07-13-2017, 10:48 AM   #17
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No dice. Looks like the clutch is duff or jammed. I will try to dismount it without disconnecting it - it is possible so I will let you know with photos. Thanks for the diagrams
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Old 07-13-2017, 11:10 AM   #18
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if you never had voltage at the compressor then even if your compressor works fine it won't kick on.

With no voltage I would suspect low refrigerant is a potential issue and the pressure switch is stopping the compressor from kicking on. That said jumping the compressor should have turned it on since you are bypassing that switch.

get some manifold gauges and check your pressures, and while you're at it add some dye to the system so you can also check for leaks at the same time
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