Manager Forum

This is a G3500 cab and chassis that is a 16 passenger bus. Has factory ac in the dash and an added Carrier inside roof mount auxiliary unit in the back. Powered condenser under the side of the bus. Front condenser has been bypassed.

Came to us with a hot electrical odor. AC clutch was burned up. When went to replace clutch ( compressor is buried on bottom right side of engine ) found that the compressor was seized up.

Sold compressor, accumulator and expansion tube replace with system flush, Did not however attempt to flush through rear evaporator and expansion valve ( block style ), no evidence of contamination at that location.

Evac and recharged with amounts listed on label from bus manufacture – 5.5 lbs and 11 oz of oil. Compressor would engage for a few seconds then not come back on. Hotwired low pressure switch and compressor ran well, no biggy that a new switch wouldn’t fix. BUT…..high side pressure would go to about 110 – 115 psi and low side pulled into a vacuum. When shut system down it would not equalize. Rechecked everything, scratched head, pulled hair, all the usual stuff. Determined had bad compressor.

Replaced compressor and orifice tube. No sign of contamination. Confirmed flow with air pressure throughout system both directions.

Evac and recharged with same results. Called compressor manufacture, Cold Power, and they said probable high side restriction.

Broke open the system again and flow tested with air both directions on all components. Replaced expansion valve on rear unit, precautionary. Recharge with same results.

Don’t know what I am missing here. Any and all suggestions and ideas are welcome. Ready to try most anything at this point.
I’m still inclined to think bad compressor. With compressor on bench fresh out of the box, add small amount of oil and rotate compressor it will not create a suction on low side or any pressure on high side. Don’t know for sure if these compressors should do that or not. I think they should. Compressor is a Nippondenso 10S17F.

sounds like another comp issue to me also. My experience tells me that when spinning clutch on bench it should have vac on one side and want to spit the oil out the other. When I've pre-oiled them on bench I always spin them to circulate the oil a little and sometimes wrong hole that spits it out. Have held fingers over them also, vac and pressure. Good luck. Maybe try different brand.

If compressor was not functioning, it would be closer to having the gauges being equal. I would try overcharging it by a pound and see what the pressures are doing then.

If suction goes to a negative you have a blockage somewhere. You may be able to blow through it but not pull s suction through it. The debris may be acting like a one way valve. You may have a collapsed sleeve in the low side somewhere inside the hos e and it's going to be a bear to find. Basically i would break out my old a/c line maker and have at it.

I considered the possibility of an internal hose issue but this being barrier hose and being able to blow through it in both directions kinda discounted that theory. Did not completely pur it out of mind but just can't see it happening like it could on the old rubber hose.

Don't give up on me. Still looking for ideas.

The hose used in the install may in fact be an older hose. It's about the only thing that makes sense. I've seen newer hoses with the plastic sleeve cracked or separated from the hose. Look along the routing for any sharp bends or damage.

Sorry I have not posted this earlier. Wanted to make sure that it stayed fixed and I have not spent much time in the office since my last post with being out of town to help my sister celebrate her 50th wedding anniversery, then took an Alaska cruise. The day we got back our daughter, son-in-law and grandkids spent a week with us.

Anyway, back the subject.

The underhood label from the bus manufacturer called for 5.5 punds of refrigerant, which we were charging to. The first two compressors would not develope pressure or suction on the bench. The third compressor, a different manufacture, would develope pressure and suction on the bench but still got same results as far as pressures and air temp when installed.

We decided to slowly add refrigerant to see if anything would develope. It slowly started to cool and pressures came to normal. It finally functioned well after charging with 10.5 pounds or refrigerant.

Live and learn I guess.