AC Compressor

MBRZ71 · May 21, 2023

A few questions about the AC compressor. It looks like the AC compressor clutch isn't activating on my 1997 K1500 5.7L.

The fuses look good and the relay was swapped with the one next to it and the clutch isn't engaging on the compressor.

To check for power of the plug going to the compressor do I need the truck running?

Do I need to put the multimeter ground to the plug or just ground on the truck body to check for voltage to the plug?

Trying to follow the instructions from this video/thread:

ac clutch does not engage

I got truck in garage around -10 or so with doors open. its a 1991 5.7 . while running I press the ac on inside the cab. all I see is ac blinking on and off. I am trying to engage the clutch. is it possible it is too cold to engage the clutch etc? I somewhat read it has...

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thx1138v2 · May 21, 2023

Your low pressure side sensor is probably failing to have enough pressure. There is a switch, typically on the accumulator, that will open so the clutch does not engage and tear the compressor up when the pressure in the system is too low. If that's the case, you won't be able to measure any voltage at the clutch.

Disconnect the pigtail from the switch and jump the two connectors with a small piece of wire. Then start the engine and observe the clutch. If it is engaged, quickly turn the ignition switch off so you don't do any damage. Then get a can of refrigerant (probably 134a) and hook it up to the port on the low pressure side, make sure your jumper is in place and start the engine again. That's how you get the system to take a charge of refrigerant when the clutch won't engage - bypass the low pressure switch.

Shut the engine off again and disconnect the refrigerant can and your jumper wire and reconnect the pigtail to the low pressure switch and try it again. Repeat until the clutch stays engaged when the pigtail is connected to the switch.

Once you get it working, you'll need to do some diagnostics to find out why the pressure was low in he first place.

PlayingWithTBI · May 21, 2023

How about simply putting a set of manifold gauges (or at least the cheapy gauge you can buy with a can of refrigerant) on it and see if it has over ~25 PSI pressure. If you don't have any pressure and, you jumper the LP switch, run the engine, you'll damage the compressor. It relies on refrigerant, as a carrier. to flow oil through and lubricate it.

If you do jumper the LP switch, you don't necessarily need the engine running to hear the clutch engage.

You're asking for trouble just randomly adding cans of refrigerant without gauges to tell you what's going on with the system.

Jeepwalker · May 21, 2023

Yeah, wouldn't be a bad idea too check the pressure first. Some parts stores sell a simple gauge ...like a tire gauge, you can test system static pressure with, if you don't want to spend too much. Some refrigerant cans even have a gauge on them. If you have a set of gauges, use them.

Also, you can also hook up a can of refrigerant to the AC port, put the can in a pan of warm/hot water (vehicle off). The refrigerant will *jump* right from the can into the AC system!! LOL

You may need to start the vehicle to draw the last bit into the system depending on it's state of charge.

Schurkey · May 21, 2023

Or just rent the proper manifold gauge set from the "loaner tool" section of various parts-stores.

I've gotten loaner-tools from NAPA, AutoZone, and--mostly--O'Reillys.

MBRZ71 · May 22, 2023

I did the loaner tool this morning with my local parts store.

I hooked up the gauges (following a video) with nothing running.

You must be registered for see images attach

Temp was about 85 F and 37% relative humidity.

I don't think I hooked it up incorrectly. I did my car first and it read about 60 psi on both sides with nothing running. I'm guessing there's a feature that prevents things from running when pressures are too high also.

Flush the system next?

tayto · May 22, 2023

perfectly normal for the gauges to read the same pressure when the system has been sitting static

PlayingWithTBI · May 22, 2023

Do you have a volt meter? Now that you proved you have pressure (lots of it), you can start up the engine and turn on the A/C. If the compressor doesn't run, pull the LP Switch connector and see if you have voltage on one of the leads. If so, try to jumper the connector and see if the compressor runs. If so, you probably have a bad LP Switch. If not, go to your service manual and trace down further in the circuit(s) to find the culprit. Good luck!

MBRZ71 · May 22, 2023

PlayingWithTBI said:
Do you have a volt meter? Now that you proved you have pressure (lots of it), you can start up the engine and turn on the A/C. If the compressor doesn't run, pull the LP Switch connector and see if you have voltage on one of the leads. If so, try to jumper the connector and see if the compressor runs. If so, you probably have a bad LP Switch. If not, go to your service manual and trace down further in the circuit(s) to find the culprit. Good luck!

That's not too much pressure to try and run the system?

Where is the LP switch connector?

PlayingWithTBI · May 22, 2023

MBRZ71 said:
That's not too much pressure to try and run the system?

Not when ambient temps are high, use the chart posted here,

AC clutch cycling on low fan setting.

Hi guys, I just finished redoing my AC. In my 99 2 door Tahoe with no rear AC. I went with a Delphi compressor, ACdelco dryer, hoses and a rockauto condenser and a 4 seasons orifice tube. Everything went smooth..added 32 oz of Freon and it’s blowing really good. Only issue I am having is the...

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AC Compressor

MBRZ71

Newbie

ac clutch does not engage

thx1138v2

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PlayingWithTBI

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Jeepwalker

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Schurkey

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MBRZ71

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tayto

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PlayingWithTBI

2022 Truck of the Year

MBRZ71

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PlayingWithTBI

2022 Truck of the Year

AC clutch cycling on low fan setting.

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