The other day, I drove my truck and the A/C was working great. This morning I got in my truck and no A/C. The blower and everything is working, but the compressor isn't kicking on. I was thinking maybe the pressure was too low, maybe a leak. Got some dye but it wouldn't take it. Got to the house and hooked up a gauge and it immediately pegged the gauge, way too much pressure. Relieved the pressure and the compressor never kicked on. Started checking power to the compressor. I have no power to either of the 2 plugs on the compressor. Not exactly sure which one is supposed to supply power to the compressor. Started checking fuses. Started with the fuse box under the hood. Everything was good except Maxi fuse #17. Looking at diagrams, this fuse has nothing to do with the air conditioner. Checked the fuses under the dash and all were good. Can anyone provide some insight on this matter? It's too damn hot no to have air.

 

Sounds like either the air gap on the compressor or the low pressure switch crapped out....

You can jumper the low pressure switch temporarily for a test .

 

Which one is the low pressure switch? and How do you do it? Also, will there be power to the plug when ever the A/C is on, or just certain times?

 

There are 2 pressure switches , high & low . IIRC the low pressure switch is on top of the compressor. With the air on & truck running , unplug the connector & use a clip lead to test the switch momentarily ...

 

I like the little insulated paper clips for that. I keep some in the truck for such bull. Anyhow if you have it all running and the ac unit to run and no fuses open then if the pressure switch Rick's speaking of is jumped then the clutch will engage regardless if the pressure is too low or if the swtich has failed. I have personnally never seen a bad pressure switch on a AC system. Usually its some other reason.

I have had my share of temperature switch failers though on other engine components.

Earlier mentioned was that the pressure was really high when checked. That has my attention- what was really high?

 

Mine will quit and I tie it back with plastic ties. In other words, pull on the plug. Mine is back and a little to the side. Play with it by pushing it around and see if the clutch engages. Rubber Duck has a mod for the 'loose' switch by putting in a few strands of copper wire to tighten up the plug. All though, this might not be your problem.

 

I don't know exactly what "high" is. I had the gauge that connects directly to the 134 can. I'm sure it is not the most accurate gauge. But when I connect the hose to the low side, The needle on the gauge goes all the way around and pegs against the back side of the pin.

As far as which plug to jump. Would it be the one towards the front of the truck or the back of the truck on the compressor?

 

please dont take it the wrong way at all but if you dont know much on how an a/c system works, you shouldnt be messing with bypassing safety high/low cutoff switches. not knowing what your doing on a pressurized system like that can result in serious injury to yourself.

but as far as the quesiton goes, get a good wiring diagram, start at the low switch see if you got pressure before and after the switch, if thats good, move to the high switch, and then the compressor and so on. thatll tell you where your power is getting stopped at. it could be something as simple as a cutout switch or a lost connection, but getting a voltage meter on the wire will tell you what it is. if i remember correctly the green wire is the one that should have power

 

You probably should have a real set of refrigerant gauges hooked up before you start letting pressure off. If the compressor is not running more then likely the pressure on the high side and low side have equalized and the reading would be high. You can pick up a set of refrigerant gauges for about $100 maybe cheaper if you shop around. But that is only a small part of it. I'm no expert but I know you need gauges if your going to work on your AC.

 

Be careful and good luck.

 

The low pressure switch on my dad's 97 failed once. You can check the switch with a multimeter. It should read 0 or very close to it when you do an ohm reading. If it doesn't, the switch went bad. The nice part is you don't have to relieve the pressure to chance the switch out.

IIRC, both switches are in series with the compressor clutch so if one fails, the clutch won't pull in.

 

Did you try pulling the plug around? You might think I'm crazy but its a problem that has been discussed many times on here.

 

Manifold Gauges. =)

yeah, you can get a cheap set for 80-100
They have short leads, but they work.

 

Good Idea...

 

Thanks for all of the advice and guidance. I'm going to get a set of gauges today. I know that when I used my Multi meter on the plugs on the compressor, both plugs seemed to be dead. That's why I started checking fuses.

I take no offense to the comment about not knowing much about the a/c systems works. However, I have already learned so much about my truck through this website. I get more satisfaction out of doing my own repairs, not to mention (usually) save myself some money.

I feel like repairing my a/c is something that could do. I learn a little from every post that I read on this sight.

Again, thanks for all of the input.