2007 Expy suddenly without AC

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Superhuman

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Hi all,

Yesterday was a warm day, and our AC was working great. Today we loaded into the truck for the first time since late last night, and no AC at all.

This spring I had to have the refrigerant recharged, but since it was working well yesterday, I don't think it's so low that it won't work at all. But hey, I'm no mechanic, so maybe I'm way off base.

In any case, the compressor isn't engaging at all. I can watch the pulley and nothing is happening. I know it can be anything between the computer and the AC, but I don't have the tools or the pin-outs on the AC relay (5L3T-AA) to test the relay or the fuse block to see if the computer is sending a signal at all.

I was wondering what you, the experts, would do in this situation? Does anyone have a diagram of the relay pin-out so I know what or how to test it?

Also, I have a question about removing the compressor clutch assuming that the electricals prove to be sound. When I turn the bolt in the clutch, the compressor just turns over. Is there a special tool for holding the pulley fixed while you turn the bolt or is there more of a "trick" to it?

Thanks,
SH
 

stamp11127

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If you want to fix it yourself you will need tools. The first thing to get would be a good test light. Forget about the clutch at this point. But you do need a clutch holding tool to remove the clutch.
 
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Superhuman

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Am I completely off-base about the refrigerant, or is that where I should be focusing? Without the compressor engaging, I'm sure that the pressures measured there (I have a cheap gauge from Wal-Mart) aren't informative.

I have tools, but I am not a well-outfitted mechanic, that's what I'm trying to get at, like the clutch-holding tool mentioned. What do I do with the test light for now? I am afraid of probing the wrong sockets of the fuse block for fear of shorting out the computer, so I'd like to know which sockets are to energize the coil in the relay.

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stamp11127

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You would use the test light to check for power on both sides of the fuse and to see if the compressor is getting power. You need to know the low and high side pressures to diagnose your problem.

If there is a leak, all of the refrigerant will leak out resulting in low to 0 pressure. Below 25psi on the low side, the pressure switch opens and kills power to the compressor. Finding a leak requires uv dye, uv light , injector tool and uv glasses at the least with the possibility of a sniffer for areas you can't get to.
 
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ExpeditionAndy

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The quickest thing to do is check the pressure. Put your cheap WalMart gauge on the low side line (the fat tube) and see if you register any pressure. If you don't have any you have to find the leak, if you do then you have an electrical problem. (I'm assuming that your system pressure with it not running is above 25 PSIG)
 
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IMINYOURCHAIR

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TL:DR for the trouble shoot for ac clutch not engaging, Fuse>voltage in and out of low pressure switch>voltage in/out of high pressure switch>relay to engage compressor>clutch coil> freon pressures (low side pressure should be greater than 30psi to engage low side switch, high side should be less than 250 psi to close)

where I start with a no cool is with the climate control (manual or auto) you have to know if the truck is actually calling for cooling and sending this signal through the switches to the relay and that the clutch actually works.

start at the fuse for the ac compressor or ac clutch then move to the low pressure switch and look for power there, it should also read continuity as well. if there is power when in "ac" then move to the high pressure switch, same as the low pressure switch but it opens under high pressure, the power will then go to the relay that sends power to the clutch to engage the compressor, I usually have the truck on and remove the relay with the ac on and feel for it to click on/off as I pull it for me it's quicker than using a test light but you may choose to use a test light to see if there is power to engage the relay if you wish. if the switches tested good this relay should be commanded to turn on and you should see power to the relay coil. the fuse needs to be good to have power to the switched side of this relay. If all looks good there, try swapping the relay with something that has the same relay but is not important to the truck to run properly. ( in a gm vehicle the horn relay would work, one dodge truck i did this to, the wiper relay was the only compatible one but still helped to diag the issue and single it to a bad relay), if the entire circuit to this point seems good, you will want to check the resistance on the clutch, I don't have an expected value but it should read something and not open.
 

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