03 2500. No A/c, stopped blowing cold. Checked fuse, good. Getting no 12v to compressor. Checked A/C relay, found 12v on pin 30 coming from fuse but no voltage out of pin 87 going to compressor. Its my understanding that this should be hot at all times with the key on. Applied 12v to pin 87 and got 12v at compressor. Looking at the wiring diagram, it shows a device PTC NO. 1 which looks like it supplies the ground or control voltage to the relay. Can anybody tell me what this is and where to find it? Any thoughts would be greatly appreciated. Also what is the TIPM, is it the power distribution unit below the fuse box?

 

So is your AC clutch not engaging? Does your orange light come on by the snowflake button on the controller?

 

Is it actually called PTCM 1 and if so that would be the Power Train Control Module block 1 I believe.
On my '03, the passenger side firewall area has three big electrical connectors that plug into the PCM. In the past I've had corrosion stop things like OD stop working, and stuff like you're having an issue with.
Disconnect the batteries, unplug those connectors, spray lots of contact cleaner on them one at a time and plug & unplug them a dozen times to scrape off the corrosion and after blowing them clean with CC, use compressed air and blow off those block connectors one last time, then plug back in and power up your batteries. Hopefully that will eliminate that issue and maybe a couple more that were ready to happen.

 

the clutch does not engage and the snowflake lights up

 

Just a thought.......have you checked the wires going to the compressor and looked for any chaffing or a broken wire?

 

I was able to apply 12v at the A/C relay and got it at the compressor so I think the wire is ok. My problem seems to be the A/C relay is not working. I swapped relays and that is not the problem. I am not getting the signal for the electromagnet in the relay for it to work.

 

Gotcha. Have you actually Ohm'd the coil to see if it's bad? Just throwing cheap and easy things out there for you to check before you go spending lots of money.

 

I haven't looked at the schematic for your truck specifically, but typically the HVAC control unit will energize that relay when there is a demand for A/C, and all the pressure and temperature switches are in the proper state to agree with the demand. It's possible your system has lost charge, or a pressure switch or sensor within the system has failed.

Am thinking PTC 1 may be a Positive Temperature Coefficient, which could be a resettable fuse or circuit protection device somewhere in the system. Possibly the clutch coil was drawing too much current. If you have access to a service manual, you can hopefully dig up some info.

 

Dang.....if this guy hasn't got some information!!!!! Obviously he might be on to something. Did your A/C just quit altogether or did it gradually get warmer and then stop?

 

The air was blowing cold then warm no gradual change. I changed the clutch and compressor last summer. I do have a haynes manual but its too generic to be useful for this type of problem.

 

I'd check your Freon pressure. Sounds like a pressure switch has tripped you off............


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my understanding is the compressor should have 12v all the time. The diagram says hot at all times. By disconnecting the connector at the compressor I have effectively isolated the clutch and compressor. There is no 12v there. I can apply 12v at the relay and it gets to the clutch connector. However my relay isn't supplying 12v on its own. Anybody know how it works

 

08 2500 6.7
AC stopped blowing cold, compressor wouldn't engage. little snowflake light is on, freon pressure is good, fuze is good. took it to a shop and they told me that "One of the pressure switches isn't getting voltage". Their electrician wasn't in today so I'm supposed to take it back on monday. I tried to trace the wires to check for anything obvious but no such luck. any suggestions would be welcome. Thanks

 

changed pressure transducer, no change. Applied 12v to ac clutch and it engages. Pressure according to cheap gauge seems too high, haven't added any freon since last year when I swapped the compressor, why would pressure go high?

 

Did you test it with the clutch engaged?
Did you test the high and low side?
What was the pressure?