New guy with AC inop question (long)

[Hairyj]

2004 1500 SLT 5.7
Don’t drive it often, last time I did AC worked. Washed the truck today (including engine bay don’t know if it’s related.

Started it to move after washing, AC inop compressor not running figured it was low refrigerant. Put gauges on fine. Checked for power to clutch coil nothing. Checked clutch coil fuse good, swapped relay good, put +12 to clutch comp runs and AC blows cold.

So
System full
Compressor runs when direct powered (I even powered it from the clutch relay terminal in the box to prove out wiring)

Best I can tell the ECM isn’t sending a ground to trigger the relay why IDK.

Another odd thing is the cond fan runs with the blower off and the control not in the defrost positions. If I unplug the AC pressure switch the fan shuts off.

Idk if it’s something they would’ve programmed in but if the switch failed high they might not run the comp but would run the cond fan.

Apologies for the long post. TNX

 

[jws123]

If you have 100% confirmed your system is full. The pressure switch could have failed you will need to test it. I have also seen the controls on the dash fail on these older trucks I have had a few where hitting the a/c button did nothing.

 

[Hairyj]

Thanks
The system is definitely full when I power the comp from the relay terminal it runs and blows cold, I also had gauges on it.

I did do a good bit of poking around and have seen references to the controls failing which I haven’t ruled out. I do know when u press the AC switch the light comes on and the comp still doesn’t run nor does it run in defrost.

It’s not a pressure switch it’s actually a 5 volt sensor and haven’t found a way to test that.

The condenser fan running all the time even with system off is puzzling as well.