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Dual A/C Project

dbshelton on Sun August 16, 2015 8:42 AM User is offline

Year: 1996
Make: Ford
Model: E-SuperDuty bus
Engine Size: 460
Refrigerant Type: R134a
Ambient Temp: 95
Pressure Low: 53
Pressure High: 235
Country of Origin: United States

Let me start by saying I know just enough about A/C systems to get into trouble.
I have a 1996 Ford 24' Shuttle bus that I now use as a car hauler. Originally it had a separate factory A/C system for the dash and a separate TransAir A/C system for the rear. I am eventually swapping engines to a Cummins diesel and want to simplify the A/C system. So far I have tied in the lines together from both units, using the skirt-mounted 3-fan 12"x48" Condensing unit, (removed the stock condenser in front of the radiator) and use only the stock Ford FS-10 compressor (about a year old). The rear evaporator has a 3-ton expansion valve (according to TransAir), the front has a red orifice tube. There is a drier with sight glass on the condenser and have the stock Ford accumulator/drier in the front. Also I have partitioned off most of the rear of the bus so that there is less volume to keep cool.
It never has cooled worth a crap, so this week I replaced the Drier, Accumulator, Orifice tube, Flushed both evaporators and the condenser, and evacuated the system for 6 1/2 hours, held the vacuum for 2 hrs, and recharged. I have no idea about how much the refrigerant and oil charge should be (TransAir was no help there but they were happy to sell me a new drier and sight glass. They couldn't even tell me what size the rear system is) so I guessed and went with 9oz of oil. I ended up at 9-12oz cans of R134a (watched pressures and checked vent temps as I added). It cools fairly well, but not as good as I believe it should.
I realize this is just a shot in the dark, but is the charge size anywhere close to what it should be? I guess the FS-10 compressor could be a little small for the application? How do I tell for sure?
I was thinking about maybe using a TM-21 compressor when I do the Cummins diesel engine swap but that's a few months away.

Edited: Sun August 16, 2015 at 8:52 AM by dbshelton

dbshelton on Sun August 16, 2015 9:43 AM User is offline

I rechecked pressures this morning:
Outside temp: 77 degrees
Pressures: 78low/78high
Pressure running 1500rpm and stabilized: 37low/160high

Still low on freon?

Edited: Sun August 16, 2015 at 8:16 PM by dbshelton

bohica2xo on Mon August 17, 2015 1:14 PM User is offline

What was the original secondary compressor?


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

dbshelton on Mon August 17, 2015 2:25 PM User is offline

It was a Sanden but I'm not sure what the model number was. SD7H15 #8105
Went ahead and added about another can of freon. Feels pretty good now.
outside temp is 95
vent temp 66
pressure 53/228
1500 rpm

Edited: Mon August 17, 2015 at 6:52 PM by dbshelton

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