AC troubleshooting / Low Pressure Switch

[pinmode]

My AC was working one day and not the next. R134a pressures look fine at rest using manifold gauges, so I don't think it's a leak. The compressor clutch does not engage. It does engage if I manually give it 24v from the truck batteries. That pushed my attention to the low pressure switch or electrical connection to the switch.

The part I'm concerned about is that when I unplug the connector to the low pressure switch and jump the connection with a paper clip, the clutch still doesn't engage. The connector does show 4.95v on the multimeter. I don't know what is on the other end of this that might be malfunctioning. It's in the dash, so I hope I'm just performing this test wrong and the problem is actually the pressure switch.

If it does turn out to be the pressure switch, it looks like the refrigerant has to be drained because there is no Schrader valve/O-ring setup on it. Can anyone confirm that? I started to unscrew it but heard the R134a escaping, so I assume that it has to be vacuumed to change it out.

One more thing - the switch part # is RD-5-9165-0. Is there a good way to source this or an equivalent? I'm only seeing the whole AC package out there.

 

[simp5782]

Red Dot still sells the switch.

What is the continuity on the compressor wire?

 

[pinmode]

Red Dot still sells the switch.

What is the continuity on the compressor wire?

On a second test the clutch does engage when the pressure switch connector is jumped. I must've been doing it wrong the first time. I'm not sure about the continuity question - from where to where?

Yes, Red Dot sells that switch for $250! Pretty wild. Especially if a 3 year old copy is broken. I decided to buy a new Sanden 4402 and have a shop install it with a new belt and new refrigerant. After the R134a is vacuumed, I'll see if they can remove and test the pressure switch. I heard today from a parts dealer that Red Dot has a minimum order of $5,000. Not sure how to get one even if I'm prepared to pay $250.

 

[simp5782]

On a second test the clutch does engage when the pressure switch connector is jumped. I must've been doing it wrong the first time. I'm not sure about the continuity question - from where to where?

Yes, Red Dot sells that switch for $250! Pretty wild. Especially if a 3 year old copy is broken. I decided to buy a new Sanden 4402 and have a shop install it with a new belt and new refrigerant. After the R134a is vacuumed, I'll see if they can remove and test the pressure switch. I heard today from a parts dealer that Red Dot has a minimum order of $5,000. Not sure how to get one even if I'm prepared to pay $250.

If your compressor was not coming on when you jumped at the switch then you would continuity test that wire from the switch to the compressor to see if it's broke. Apparently it's not if it's on.

I have been able to order parts thru a red dot distributors in the past for small stuff unless something has changed

 

[pinmode]

Gotcha! So from the connector to the compressor. Thanks. I need to buy some longer probe wires.

I'll check other distributors to see what they say. Ranshu in Reno said they're not really open to the public, but the guy working there still tried to find the part. Order minimum was still an issue though.

Thanks for the help!

 

[simp5782]

Find out the pressure rating on the switch. Its probably a common civilian replacement. You may even try mobile climate control

 

[pinmode]

I was on the wrong track. The issue turned out to be a stuck blend door or maybe actuator. I don’t know exactly because rather than tear apart the dash and try to source the part, I had a coolant shutoff added so the heater core can be bypassed entirely. This worked and I have cold air now, which I think confirms that the blend door/actuator is the problem.