How do I test the AC pressure switch?

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Old 06-17-11, 02:50 PM
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How do I test the AC pressure switch?

2005 Impala--compressor clutch not engaging. I can pull in the clutch by removing the clutch relay and jumping the contacts so the problem is upstream of the relay coil. I suspect the refrigerant pressure switch but there are 3 terminals down inside the switch and it's very hard to reach--not up top like in other cars I'm familiar with. Which of the 3 terminals on the connector do I jumper to activate the clutch relay? Measurements on the disconnected plug find 5V on the gray wire, ground on the black and nothing on the red. All fuses & relays check OK.

I'm afraid to simply stab a jumper across the 5V & the others in case it goes to the body computer instead of a simple interlock on the relay coil.
 
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Old 06-17-11, 03:18 PM
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The usual way of testing the pressure switch is to service the a/c system to know whether the system pressure is above or below the switch setting.
 
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Old 06-17-11, 03:52 PM
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Tried that. Took it to mechanic & he said it's an electrical problem & he doesn't do electrical Hoping for a quick fix so I can take the car on vacation Sunday instead of taking my truck.
 
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Old 06-17-11, 04:53 PM
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try going to a parts store and finding one in stock. they usually have wiring diagrams for the switch in the box. yeah, not like the g'ol ones with 2 prongs, aye?
or look up wiring diagram in a library.
 
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Old 06-17-11, 04:59 PM
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I'll also add I have over 85psi static on both gauges at 72F ambient.
 
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Old 06-17-11, 05:03 PM
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Originally Posted by ukrbyk View Post
... yeah, not like the g'ol ones with 2 prongs, aye?
...
And what's up with that--does it test low and high pressure now?
 
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Old 06-18-11, 05:37 AM
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Nobody in a sharing mood?
 
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Old 06-18-11, 03:59 PM
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Originally Posted by guy48065 View Post
And what's up with that--does it test low and high pressure now?
NO, THERE WERE SIMPLY VERY EASY TO JUMP. no guesswork. and you should have about 70% difference in pressures between the lines.

also, Google usually works well:

YouTube - ‪HVAC High Pressure Sensor Testing‬‏
 
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Old 06-18-11, 05:54 PM
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Originally Posted by ukrbyk View Post
...and you should have about 70% difference in pressures between the lines.
Not for static pressure. If I could get it running, then yes.
 
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Old 06-18-11, 07:45 PM
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I am pretty sure that the PCM (engine controller) actually controls the a/c clutch.
it uses inputs from various sensors to determine clutch status.
you better find a wiring schematic- or chance of damaging something!
have you tried to register your vehicle on the autozone website?-they have online manuals.
 
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Old 06-18-11, 07:49 PM
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Originally Posted by guy48065 View Post
I'll also add I have over 85psi static on both gauges at 72F ambient.
so it has refrigerant in the system-enough for the low pressure sensor to close contacts
 
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Old 06-19-11, 07:21 AM
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Originally Posted by guy48065 View Post
Not for static pressure. If I could get it running, then yes.
i don't think you even should measure "static" pressure. but it's whatever. by now, you have all info, i think, including how to test the switch with 3 prongs, aye, mate? btw, i have jumped that switch, in 2 prong config, on multiple makes, and ECU never had any issues with me doing this.

This A/C Manifold Gauge Set is designed to test automotive air conditioning systems (using R134A Freon only) by comparing the "high side" and "low side" pressure reading to the vehicle manufacturer’s A/C system specifications. The high-pressure gauge measures compressor discharge pressure, and the low-pressure gauge measures suction.
 
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Old 06-19-11, 07:46 AM
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Originally Posted by ukrbyk View Post
... you have all info, i think, including how to test the switch with 3 prongs, aye, mate? btw, i have jumped that switch, in 2 prong config, on multiple makes, and ECU never had any issues with me doing this.
Didn't get any info on the sensor from this forum but luckily aircondition.com has its own forum and I got a knowledgeable reply there. My sensor is a actual transducer that outputs a signal proportional to the pressure. Jumping the contacts could damage the computer.

So in the end I can't take my car on the trip but at least I did get enough useful information to be able to eliminate the obvious easy stuff.
 
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Old 06-19-11, 08:10 AM
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i am very sorry 3 terminal switch check video i posted here did not work for you. glad you had it fixed.

for the sake of others, i'll drop in some info:

all those switches are transducers. it's a fency word for something that converts one type of energy (in this case - pressure) into another type of energy (in this case - electricity): A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered as a transducer.

a/c pressure switch simply senses level of pressure applied to its end, called bulb, and tells the system if it's at specific level, safe enough to run compressor:

A thermostatic expansion valve is a metering device that monitors the amount of refrigerant that enters an A/C's evaporator. When an air conditioning unit switches on, the compressor transfers refrigerant in gas form to the condenser. The condenser switches the gas refrigerant into a liquid refrigerant. The liquid refrigerant leaves the receiver-drier and enters the expansion valve pressure switch.

The expansion valve has three points of pressure that work together to regulate the amount of refrigerant that enters the evaporator so it complements the amount of refrigerant burned off by the evaporator. The valve pressure switch receives pressure from the bulb, the evaporator and the spring. The evaporator and spring pressure work together to close the valve. The bulb pressure opens the valve. When the expansion valve pressure switch decreases pressure at the bulb, the valve closes. When pressure increases at the bulb, the valve opens.



 
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