TXCTD01

So I posted a few days ago that my A/C was only blowing hot air and the compressor would not kick on. I had a guy today put gauges on and it has pressure but the compressor is not kicking on. I'm thinking it might be one of the pressure switches. So my questions are:
1. Do these trucks have a high side and low side switch or just one or the other?
2. Where are the switches located? I see one above the compressor but not sure if that is the one I need to test.
3. Lastly, what is the exact name that I need to use to ask for at the autoparts store? I tried looking online but wasn't sure what the exact name of the part is.

Once again thanks so much for the help!!!

Mr Jerry

I guess you didnt belive me when I said you should check your comp-coil, there is a 95% chance thats the problem. takes about 90 minutes and about 30 or 40 dollars to replace.

bradler

it has pressure but how much on high and low side? low pressure switch will keep comp from kicking on if undercharged...

Chris Taylor

^^

I would have the freon checked first before throwing parts at it. I see it everyday in the shop, someone comes in swearing that the compressor is dead but it just needs more freon.

Sevir

what are your pressures? for your compressor to come on, your low side PSI should read at least 20psi. How did this tech check pressure? the proper way is to drive it around for about 10 mins then put gauges on it. your low side should read 30-40psi while your high side is current ambient temp x2 +10deg every 10% past 50% humidity. that might be a little confusing, here is a example. if the current ambient temp is 80deg with 60% humidity, your high side should be around 170psi +/- 20psi. But if you do have pressure and your compressor isnt coming on, it can be two thing, your pressure switch or your clutch assembly. The bad news with our compressors is the clutch isnt replacable, you have to get a complete compressor.

SpeedyWS6

There are so many things on newer vehicles that will prevent your compressor from engaging. A good scan tool is almost as important as a set of gauges.

Static pressure should be over 60 (very dependent on ambient temp) on a hot day with a hot engine it will probably be over 100psi with a full charge. Over 60 though and that is plenty of pressure to at least get the compressor to engage a few times.

The evaporator core temp sensor is a pretty common failure on our trucks, and it will not let the compressor engage if it does fail. You need a scanner to verify.

The coils on the compressor is also pretty common. You need to check power and ground to the clutch to verify. No power, the problem is somewhere else.

You also need a scanner to verify that your pressure switches are reading close to your actual pressure on the gauges. I have seen them get way out of range and the compressor will not engage due to the computer seeing very high or very low pressures.

nedz19

I have been having problems with mine too. I did pull a code off it and I'm pretty sure it was a PO533. I have it wrote down at home but dint have it with me right now. AC pressure sensor high input. Check voltage at the compressor and didn't have anything. Static readings on the gauges looked good. I'm thinking the high pressure sensor maybe bad but wanting some reassurance if anyone is willing to help me out before I drop 100 bucks on it. Not to mention that I hear it is OEM only.

Mr Jerry

If you bridge a wire across the conector on the pressure switch down by the compresser, that should turn on the compresser, if it doesnt turn on, check for resistance on the cluch coil by disconecting the 2 wires and checking and seeing if there is any resistance in the clutch coil, if not buy a coil on e-bay 40.00 and about an hour and your done.

Spooler

Yeap, what he said. Jump the wire on the pressure switch right above the compressor. Easy.

nedz19

It's a three wire connector. Which two are you supposed to jump?

Spooler

Have to get under my truck and look. It will the weekend before I could offer help on this. Most of the time it is just a 2 wire switch for high/low pressure.

nedz19

That's what I thought too but I looked ad ha my truck mech at work look and it's three wires. Got a new one comin in tomorrow and hopefully that will fix the prob. I appreciate the info though.

Mr Jerry

Sorry I havent looked at the switch for so long I thought it was a 2 pin switch, not a 3 pin,,I would just check for resistance through the clutch coil first, just pull fender liner unplug the compresser conector 2 wires and check if any resistance in those 2 wires going to the compresser, if no resistance replace the clutch coil, its sold on e-bay 40 bucks, sure wish i had thought about takeing pics when i did it, real easy job.

SpeedyWS6

Just an FYI, just about any newer model vehicle has a true pressure sensor no more switches, they work off a 5 volt reference signal. If you have access to a good scanner (it takes a pretty good one) you can look at the pid for the pressure sensor.

nedz19

Put a new pressure sensor in. Didn't do the trick