My99

Well, I've been trying to figure out my a/c problem over the past week. I can't get my a/c compressor to kick on. Well, tonight I got bored and I went and unhooked the plug from the compress or that hooks to the harness. I then turn on the truck along with the a/c switch, and went back under the hood and stuck my volt meter on the side of the plug that runs off the wiring harness. It showed only .02 volts. Or in other words, nothing. With the truck off, it showed zero volts. So... this tells me there's no voltage running through this wire in the harness to even tell the compressor to kick on. My question is SHOULD there be 12 volts in this wire at any time? Or is there some other swtich or sensor in the circuit that would keep the 12 volts from flowing through here?

Just as a test I turned the truck and a/c switch on again, and with the harness unplugged I connected a wire from the comporessor side of the harness up to the positive battery terminal. Immediately the a/c compressor started turning, and sounded normal, making me think that the compressor's just fine.

So, I'm left at a loss here. Does anyone know where/what to check next? Does 12 volts flow through to all accessories in the truck? If I were to wire up my own switch for the a/c, from the battery, would this in any way harm the compressor? I'm not saying I'd do this, just looking for theory mainly.

EDIT: Something just occured to me. I know there is an A/C fuse, but is there also an A/C relay? If so, where is it, and how would I check to see if it's good or not?

AverysDad

the compressor has to be able to cycle itself on and off when the a/c is on otherwise you wont get very good cooling...........there is a switch that tells thecompresor to run but it only will turn on if the pressures are correct ..............you probably have a leak and have low pressure therefore the compressor is not kicking on by itself

My99

I've established it's not leaking and pressure is holding. What other fail-safes are there that would keep voltage from flowing out of this wiring harness and kicking on the compressor? Where is this switch located that tells the compressor to run or not? Perhaps there's an issue there.

WT

Hmm low pressure switch could be bad if your at the right pressure.. it may not be switching so it wont let the voltage get to the compresor.. worth a try and I would think easy replacement.

My99

I've got a toyota manual here that says there's an "Air Conditioner Control System", fuse number 17, which is a 40 amp fuse. I'm unable to find this one. I was able to find the "Air Conditioner" fuse, which is a 10 amp fuse behind the glove box. This 10 amp fuse is fine.

My99

Just found what MAY be a crucial part to the puzzle. Ever since i put my engine back in, I could not find what this plug from the wiring harness was hooked to.



I'd forgotten about this until tonight I was rummaging through some old digital photo's and came across it. SO I went out to the truck and tested it with the volt meter. With the key "on" i tested it, and it put out .02 volts. Same as the other wire did that led to the compressor off the wiring harness... hmm. So, I turned on the blower motor and this plug all of a sudden read 12.XX volts. Full voltage. Whether the a/c button was on or not, it did not change the voltage. SO... what I'm thinking is this is some sort of switch that only supplies power to the compressor if the fan is ON, and when the fan is switched off it does not supply any power to the a/c compressor, so that you're not wasting fuel by running the compressor without the fan.

This leads me to my next question. I cannot find where in the heck this plug hooks on. IF anyone could help me out I would be eternally grateful. It comes out of the wiring harness around the same spot as the fuel injector plug, back towards the firewall on the driver's side of the engine. Please help me, this could just be it!

Thanks!

Waterboy

I went out and scurried around my engine for 15 minutes and couldn't find the connection you were talking about. Sorry. With the headers I had a really good view of the area too. If someone doesn't find it by tomorrow I'll look some more in the day light.

My99

Hey thanks a lot! I've been my head on this one for a while, but I think it might just be the culprit.

98 Joes

I think I have it for you. I looked at mine and found that there is plug that looks just like that one, on my rig. It has a pink wire coming out of the plug. It's plugged into the water temperature switch that is screwed into the engine just below where your plug is and all those hoses in you picture. A real PITA to get to. Apparently it needs to be plugged in for the A/C to work. I unplugged mine and the A/C wouldn't come on. The switch is there to read water temp and cut it off if the truck starts to overheat, by breaking the ground connection. With it unplugged, it thinks it's overheating. If you can plug it in, it might work. As long as nothing else is wrong.

And your other question about the blower having to be on is yes, the blower has to be on for the A/C to work.

Now one more thing, according to my manual, that temp sensor may have been only on trucks with automatic transmissions. So if your donor engine came from a manual transmissioned truck, it may not be there, but the provision will be and you can probably just get the sensor and install it. I haven't been able to confirm the auto/manual question. One of my books says only A/T trucks, the other says nothing about it. The one that says only A/T trucks had it, also matches the wire coloring, so I tend to believe it.

My99

Well, I owe you a round or two if you ever end up in my neck of the woods. I kinda had a similar hunch as you, but the fact that that sensor already had a plug plugged onto it sort of confused me. So, I unplugged the plug that was on there and plugged in (after re-wiring b/c i pulled the wire out of the plug) the blue plug and voila! Cold air! Thanks again for all the help. It's nice and cool now. I owe you one!

I only wonder what it was that I unplugged to plug in the right plug. Obviously the plugs were the same shape/fit but the other plug was white. Kinda odd, but hey, if it works it works.

98 Joes

Glad to hear that fixed your problem. Enjoy the cool air.