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6.9L Diesels Technical discussion of topics related to vehicles powered by the 6.9 Liter In-Direct Injection Navistar engines.

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Old 04-26-2005, 01:22 PM   #1 (permalink)
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How to know if AC compressor is dead or just clutch

TO the experts,or any one that knows more that me. How do determine what to start with to get my AC working? The system does have a leak i belive but it hasn't been charged in many year so it is empty. If I select AC on the controls the clutch never engages. Is this because it needs recharged or do you belive that the clutch is bad and or the copressor?

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Old 04-26-2005, 01:30 PM   #2 (permalink)
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Re: How to know if AC compressor is dead or just clutch

There is a pressure switch which prevents the AC compressor clutch from engaging when the system is empty.
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Old 04-26-2005, 01:41 PM   #3 (permalink)
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Re: How to know if AC compressor is dead or just clutch

Exactly, I thought the A/C was gone in my truck. When filled with refridgerant, the system started right up once the proper amount was in the system.
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Old 04-26-2005, 01:57 PM   #4 (permalink)
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Re: How to know if AC compressor is dead or just clutch

Good Deal I thought if went something like that i was just not sure. I did price the compressor and clutch and if dosn't work with just a recharge i will just go with the 2 at 55 kind of in cab cooling. Thanks for the info

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Old 04-26-2005, 02:27 PM   #5 (permalink)
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Re: How to know if AC compressor is dead or just clutch

If you have to replace the compressor, you need to replace the drier/accumulator also.
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Old 04-26-2005, 07:55 PM   #6 (permalink)
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Re: How to know if AC compressor is dead or just clutch

All you have to do to test the compressor is to jump across the wiring harness for the cycle switch. Don't leave it run for more than the second it takes to make sure it engages, or you will burn up the compressor.

But if the system is empty, the clutch will not engage. Just jumper the switch connector to make sure the clutch works, and evac the system and recharge with an R134A retrofit kit. Do not add the R134A without evac'ing the system, all you will accomplish is creating acids which will destroy the system. The oils and refrigerants are not compatible.

I have done many retrofits with no problems after evac'ing the system.
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Old 04-26-2005, 08:26 PM   #7 (permalink)
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Re: How to know if AC compressor is dead or just clutch

I have the same problem; leak, no refrigerant, but compressor good. How does one evac the system. I see conversion kits available, do these come with all needed materials/tools? If you wouldn't mind, would you mind a brief rundown on what to do to switch the system to 134A?

Thanks in advance-
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Old 04-27-2005, 09:31 AM   #8 (permalink)
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Re: How to know if AC compressor is dead or just clutch

Just had mine serviced.Thought i needed a new clutch,didnt cycle anymore and wouldnt engage.Turned out it just needed a new pressure switch...
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Old 04-27-2005, 09:56 AM   #9 (permalink)
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Re: How to know if AC compressor is dead or just clutch

One of the guys here has a great article on troubleshooting the system, maybe Mel, SARguy or Ziggy...

In short, I had the same problem. Followed the article...first step was jumping the pressure switch in the "can" which is located near the heater core lines on the passenger side. Tall black can, maybe 10-12" high, 3" diameter. There are two wires that go to a switch that screws into the side of the can. Start the engine, disconnect the connector to the switch, and stick a wire between the two plugs on the connector, see if the clutch engages.

Those pressure switches are a "weak link" on the older trucks. Turned out that was my problem...switch was $30. Screwed it in, connected the plug, and presto...cold air [img]/ubbthreads/images/graemlins/wink.gif[/img]

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Old 04-30-2005, 11:36 AM   #10 (permalink)
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Re: How to know if AC compressor is dead or just clutch

[ QUOTE ]
I have the same problem; leak, no refrigerant, but compressor good. How does one evac the system. I see conversion kits available, do these come with all needed materials/tools? If you wouldn't mind, would you mind a brief rundown on what to do to switch the system to 134A?

Thanks in advance-

[/ QUOTE ]

To evac the system you need a A/C vacuum pump or have a shop do it. I bought a relatively inexpensive vacuum pump from JC Whitney to do the job myself... I have used it on probably 5 vehicles now.

THe conversion kits that you can get at Wal-Mart, etc come with everything that you need to do the work, except the evac pump of course. The kit instructions "insinuate" that you can add the R134a to an R12 system, however that is not true. All of the old refrigerant and oil must be evacuated first. And a vacuum must be held for at least 30 minutes in order to boil off any moisture that may be in the system, particularly if the system was low or empty. An A/C system will actually pull outside air through a leaking O-ring under certain circumstances.

As far as refilling the system, that's easy. You screw on the R134A adaptors onto the two system fittings, and refill the system with refrigerant / oil.
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