P8M4108a OTR a/c question

chessie4905 · June 06, 2018, 08:03:20 PM

From my 4905, 4108 shop manual:. Refrigerant compressor Frigidaire 6 cylinder axial 12.6 cu. In. Rotation veiwing drive end counter clockwise GM part number 5910771.
12 volt clutch coil.

luvrbus · June 06, 2018, 08:18:50 PM

Where do they pick up the 12v for the clutch on a 4905

chessie4905 · June 06, 2018, 08:30:23 PM

4905 uses a big v type compressor running off a driveshaft from front end of engine. Comes off at an angle and clutch is air operated.
The dual A-6 option is belt driven and both compressor clutch units are rated at 12 volts. Wiring diagram shows them wired parallel, so I don't know if coil voltage rating is a typo or it doesn't care.
Apparently since the 4108 doesn't have a dash evaporator, it gets by with the single compressor.

richard5933 · June 07, 2018, 02:56:07 AM

Thanks for the information and confirmation that I was looking at the correct data, especially the part about the 12v clutch. After looking at the various listings online, the hard part looks like it's going to be finding the CCW rotation.

The A6 compressors in the online catalogues all list either r12 or r12/r134 as the compatible refrigerants. None that I've found show r22 as compatible. Is that simply because no one is running r22 so they don't show it, or is there a physical difference in the compressors used for r22? They look to my eye to be the same, other than possibly the oil being used.

Our 4106 had been converted to r134 at some point, and the only piece of hardware that I knew to have been changed was the compressor. Since we are going to be changing the compressor on this bus now, what would be the result if the refrigerant was changed and we left the condensing coil and other hardware in place? The rubber lines to the compressor have been mentioned as possible problems, anything else? What about functionality? Will the other components still produce cold air or am I going to need to change other things?

Or, is my original plan of just replacing the compressor and refilling with r22 the best working plan at the moment.

What's killing me here is actually the amount of time this is taking - weather right now is gorgeous and I really want to be on the road. But, we are planning to drive to Gillette WY in July though, so we'll need the a/c working by then and this is as good a time to deal with this as any.

chessie4905 · June 07, 2018, 04:40:09 AM

If you are replacing compressor anyway, it would be foolish to stay with R-22. The newer rebuilds MAY have more robust seals made from compatible material.

chessie4905 · June 07, 2018, 05:34:42 AM

I suspected this but decided to verify. Your compressor, due to its design can operate in either direction.
https://www.powernationtv.com/post/different-model-ac-compressors-and-how-they-work

Outlet and inlet ports should be same size.

richard5933 · June 12, 2018, 02:24:40 PM

This gets more confusing every day. Luke was not able to get a replacement compressor through his usual channels. Apparently the hang up is the CCW rotation. The part number we're looking for is 1131207, which is an A6 Frigidaire compressor with a 5.5" clutch, 12v, CCW, with type C ports.

I was able to find one which is nearly the same as what is in the bus, but with two minor differences. At least I hope they are minor.

The one I'm looking at is: https://truckerac.com/gm-compressor-model-a6-type-c61138002.html

The two differences are that the new one has a 6" pulley instead of the current 5.5", and the new one is filled with PAG150 oil instead of the mineral oil which is in the current one.

The pulley size doesn't seem that big a deal. Seems like it would spin slightly slower, which might create a problem at idle or low speeds, but I'm thinking that at highway speeds things should be okay.

The oil is what I'm more worried about since I don't think that the PAG150 is compatible with either the r22 or the current mineral oil. I'm hoping that it's possible to flush the PAG150 out of the compressor before installing it and then refill with the mineral oil.

Anyone able to shed some light on these two issues?

chessie4905 · June 12, 2018, 07:37:54 PM

In reply #65 and again here, the A-6 can be run either direction without changes.

http://www.refrigeration-engineer.com/forums/archive/index.php/t-40024.html

luvrbus · June 12, 2018, 08:01:17 PM

It's not the turning direction of the compressor it's the clutch engagement and I have no idea how you solve that on a A-6 compressor

luvrbus · June 12, 2018, 08:48:38 PM

I bet AP Air in IA will have what you need 800-806-5312,be for warned they can be a bitch to convince to sell to a individual but will come around most of the time

richard5933 · June 13, 2018, 02:25:02 AM

Quote from: luvrbus on June 12, 2018, 08:48:38 PM
I bet AP Air in IA will have what you need 800-806-5312,be for warned they can be a bitch to convince to sell to a individual but will come around most of the time

I'll call them in the morning.

Quote from: luvrbus on June 12, 2018, 08:01:17 PM
It's not the turning direction of the compressor it's the clutch engagement and I have no idea how you solve that on a A-6 compressor

Not sure what you mean here. The clutch seems to engage by pulling along the axis of the main shaft. My concern about the clutch was the diameter being 6" instead of 5.5" as was originally in the bus.

Quote from: chessie4905 on June 12, 2018, 07:37:54 PM
In reply #65 and again here, the A-6 can be run either direction without changes.

http://www.refrigeration-engineer.com/forums/archive/index.php/t-40024.html

That's not what I'm being told. The A6 is sold in both versions, CW & CCW. If they could turn either way, the specs wouldn't include rotation. The guy at Welch in GA told me that the oil pump is different on the two rotations, and that spinning them backwards will make cold, but the oil won't circulate and the compressor won't last last long running backwards.

chessie4905 · June 13, 2018, 02:29:02 AM

Clutch engagement? The electrical coil pulls the clutch plate in against the armature, causing the pulley to turn the internal components. Direction of rotation doesn't matter. It's just like the car model GM made, only larger. They reverse the inlet and outlet connections on the rear.

richard5933 · June 13, 2018, 03:11:24 AM

Quote from: chessie4905 on June 13, 2018, 02:29:02 AM
Clutch engagement? The electrical coil pulls the clutch plate in against the armature, causing the pulley to turn the internal components. Direction of rotation doesn't matter. It's just like the car model GM made, only larger. They reverse the inlet and outlet connections on the rear.

Like I said, I did find one that is built to spin CCW as I need, but has the 6" clutch and the wrong oil. Any idea if this one can be made to work by flushing/changing oil and using a larger belt?

Not sure how much of a difference the 1/2 diameter difference will make in performance and can't find anything online with charts or other information.

luvrbus · June 13, 2018, 05:33:48 AM

Quote from: chessie4905 on June 13, 2018, 02:29:02 AM
Clutch engagement? The electrical coil pulls the clutch plate in against the armature, causing the pulley to turn the internal components. Direction of rotation doesn't matter. It's just like the car model GM made, only larger. They reverse the inlet and outlet connections on the rear.

I have come across magnetic clutches the lining are made to engage right or left on equipment and they come apart if wrong.I have a GMC the friggin fan spins backwards through a magnetic clutch figure that one out

richard5933 · June 13, 2018, 10:26:56 AM

Quote from: luvrbus on June 13, 2018, 05:33:48 AM

I have come across magnetic clutches the lining are made to engage right or left on equipment and they come apart if wrong.I have a GMC the friggin fan spins backwards through a magnetic clutch figure that one out

Can't figure that out any more than I can figure out why GM used a 12v clutch in a bus with a 24v electrical system.