Helping a buddy - dodge AC question

[FAKKY]

Symptoms were sometimes cold sometimes nothing.
I evacuated system and vaccumed and started recharge to spec (engine on).

BUt low pressure side hit 90 psi and compressor didnt turn on.

I supplied 12v via powerprobe and compressor clutch moves. I checked an replaced fuse - all ok.

I then started looking for low pressure switch - turns out (maybe ?) the dodge 1500 [2004] doesn't have one its only a high pressure switch with some mechansim in the condensor itself for low pressure ?

How do I determine why it appears there is no signal going to compressor to turn on if there is no low pressure switch.

Any help appreciated. I'd like to get back to working on my truck.

[FAKKY]

Another bit of info.

Checked and swapped the relays. All ok.
Checked voltage at the compressor on switch ........ peaks at like 3v. I thought this was a 5V signal but not sure ...... and how that helps. But its not enough to enagage compressor ... 12v from the powerprobe does

[Dead Parrot]

My 75 C10 doesn't have a low pressure switch. It has a mechanical thermostat with a probe that fits on the cold coils. If the coils get too cold, like frozen up, the switch opens and cycles the compressor off. Possible the Dodge does something similar. If an unrelated repair loosened that connector could explain the intermittent behavior. Or a mouse taste testing a wire or two.

[FAKKY]

Originally Posted by Dead Parrot

My 75 C10 doesn't have a low pressure switch. It has a mechanical thermostat with a probe that fits on the cold coils. If the coils get too cold, like frozen up, the switch opens and cycles the compressor off. Possible the Dodge does something similar. If an unrelated repair loosened that connector could explain the intermittent behavior. Or a mouse taste testing a wire or two.

Yeah the more I read up in it seems like the low side is controlled more by this temp probe in the evap ......

Still not sure why Im seeing a max of 3V at the compressor switch. Heard problems with the TIPM ....... but think its just a bad ac compressor. Still doesnt explain the 3V.

[FAKKY]

https://www.dieseltruckresource.com/...-273835/page2/

[truckdude239]

check that the condressor fan is running the dodges are bad about the condressor fan dieing and jacking the pressures high and shutting doiwn the compressor

[Bigdav160]

The compressor is ECM controlled. There should be a pressure transducer on the A/C lines near the compressor. This is NOT a pressure switch but a pressure sensor.