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Turning compressor by hand

77shovelhead on Wed August 11, 2010 12:01 AM User is offline

Year: 95
Make: Olds
Model: 88 Royale
Engine Size: 3.8
Refrigerant Type: 134
Country of Origin: United States

I read in the instructions with the new compressor that I should rotate the compressor after adding the oil. Before draining and measuring the oil,I tried to rotate the compressor and it is tight, REAL TIGHT. The first 1/4 - 1/2 turn even had a squeak, like the seal was rubbing. I set the compressor up on the clutch end, thinking that the oil will lube the seal on the inside and no squeak but it's still tight.

I read somewhere in the Mastercool manual that some compressors can be turned by hand and some need to be mounted in a jig and a wrench used to rotate it.

Is there some way of knowing which compressors turn by hand and which ones need a wrench?

The new compressor I installed on my daughter's PT Cruiser turned by hand, but this one, for the Olds, won't.

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Quality is never an accident it is always the result of intelligent effort.

GM Tech on Wed August 11, 2010 8:27 AM User is offline

H-6 compressors after they sit for a year or so in a box are extremely tight to turn- the axial plate shoes are the culprit-they are "glued" to the axial plate from the resin used in the manufacture of the axial plate.... you would do good to just mount it and let the vehicle turn it for you if you cannot turn it on the bench.....that is what I do.....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

iceman2555 on Wed August 11, 2010 10:42 AM User is offlineView users profile

GM and some Ford compressors are almost impossible to rotate by hand.
Break-away torque for a GM H series or R4 is 175-195 in/ft...or 14 to 16 lb/ft.
A recent test of some OE GM compressors indicated that break away torque for these units exceeded 75 lb/ft.
To properly rotate a compressor prior to installation, the unit should be charged with the correct type and amount of lubricant. The unit should be mounted to the vehicle, the manifold attached and then rotated utilizing the correct tool. The 'old' way was what GM stated....lube it up....mount it up....and let the engine rotate the darn thing.....this works also....performed this process many times.
Best procedure to accomplish this....engine @ idle speed and Normal Operating Temperature, disconnect the LPCO....jump the wiring connector....a paper clip works well......engage and disengage the clutch multiple times, 12-18 is good.
Insure that the system is properly charged....increase engine RPM to app 1200-1500. Using the same procedure listed above....engage and disengage the clutch app 50 times. This is a process known as 'burnishing' the clutch. This greatly increases the initial torque/holding force of the clutch. Normal compressor clutch engagements are app 25-30 % of maximum hold force. A clutch cycle period of several hundred engagements is necessary to maximize clutch/drive holding force.
Many compressor swash plates are coated with tin. During the assembly process, chemicals are utilized to 'hold' all parts together for assembly. After a period of time, these products can actually contribute to the force necessary to rotate the compressor. R4's present their own unique break away issues...but some are the same.
This 'can't turn by hand' should not be a major factor for GM units.....if it is a quality new unit...or reman'd unit this should not be an issue.


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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson



Edited: Wed August 11, 2010 at 10:42 AM by iceman2555

77shovelhead on Wed August 11, 2010 4:13 PM User is offline

Thanks again guys.

Before seeing the replies, I stopped by Napa and checked another off the shelf compressor. It too was tight. Now I know what it should feel like. I added oil, bench mounted the compressor and turned it 10 or so revolutions and it feels good.

I just try to check everything out and know that I'm doing the best that I can. I have learned alot and forgotten almost as much.


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Quality is never an accident it is always the result of intelligent effort.

TRB on Wed August 11, 2010 5:12 PM User is offlineView users profile

We use a large vice. Open jaws enough so the hub can be clamped, not to tight. Then turn the body of the compressor. May not see this listed in the office icemann handbook. But it works well. especially when you drain the oil out as we doing from the manufactures.

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iceman2555 on Wed August 11, 2010 6:01 PM User is offlineView users profile

TRB...must admit...that is the first time for that....I think.....have to check the mental notes.
I like the one....suggest to use a spanner wrench or clutch turning tool....now both of these tools multiply the force being exerted on the drive correct.....well....the 'tech' (?) is still trying to hold the body with one hand and using the tool multipler with the other.......still think the book would be a great idea!!!!!!!!!!

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

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