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Old 04-26-2017, 09:03 PM   #1
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Coach a/c

Coach a/c (if it has one) compressor is disengaged when magnetic clutch is not energized. Has anyone seen electric motor or gasoline motor connected to bus a/c compressor and cooling the bus while main engine is off? Why have another a/c when bus already has one? What are the complications? I have never seen It done. Why not?
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Old 04-26-2017, 09:06 PM   #2
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Originally Posted by Bus Wannabe View Post
Coach a/c (if it has one) compressor is disengaged when magnetic clutch is not energized. Has anyone seen electric motor or gasoline motor connected to bus a/c compressor and cooling the bus while main engine is off? Why have another a/c when bus already has one? What are the complications? I have never seen It done. Why not?
Some coaches have separate engines for a/c.
I am no expert, but it should be doable.
Well anything is possible with a little imagination​ and a lot of money lol

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Old 04-26-2017, 09:23 PM   #3
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AC driven by smaller engines was common years ago. It just sounded like a generator running, and it produces a constant speed to power the AC unit. You don't warm up when you're idling in traffic on a hot day.
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Old 04-27-2017, 02:39 AM   #4
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Originally Posted by Njsurf73 View Post
Some coaches have separate engines for a/c.
I am no expert, but it should be doable.
Well anything is possible with a little imagination​ and a lot of money lol

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May be the space restrictions or too much money? Can't say that rooftop a/c units are cheap though.

Some have separate engines because either the bus doesn't have originally a/c unit or in some cases It is technically difficult to have in running on main engine. The more expensive newer coaches don't have that any more. The bus original a/c is a good one usually and powerful also. I am trying to think why haven't bus converters done It. The reason I would not do It is that I don't know how to make It tecnically work. In priciple It cannot be that hard .

I don't have a buus yet, I am doing my research now and I have all kinds of silly qestions but this one is not silly IMO
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Old 04-27-2017, 07:14 AM   #5
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Interestingly enough I've been thinking the same thing. Put a clutch on the compressor and an electric motor (it'll freewheel if not powered or acting like a generator, although a clutch on it as well would keep it from spinning needlessly), and good things happen....
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Old 04-27-2017, 09:06 AM   #6
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Interestingly enough I've been thinking the same thing. Put a clutch on the compressor and an electric motor (it'll freewheel if not powered or acting like a generator, although a clutch on it as well would keep it from spinning needlessly), and good things happen....
Yes, the compressor is "freewheeling" separate from the main engine now unless the clutch is energized. So I am thinking there must be a way to connect an electric motor to the clutch . It doesn't have to be automatic and hight tech, once you park your rig, you can pull some lever in engine compartment to connect the electric motor to the compressor through the clutch that is now not engaged with main engine. In order not to have the compressor running constantly and freezing you, you could use the same relay system that engages and disengages the clutch now, It would turn your AC motor on and off (inside the coach would be a thermostat). It can be done theoretically but my question is why hasn't anyone done It. There are all kinds of geniuses who have converted buses. Why haven't they done It? AC electric motors are not expensive. You probably don't have to run the air conditioner to full power since modern bus air conditioners are very powerful (I consider modern 20-25 years old, full of electronics already) so I figure 2-3 kw AC motor would do fine? I am in Europe and you could get a less than 20 years old coach with less than million km on It for 10 000 euros. It has even floor (most have middle part lower), It is close to 400 hp diesel pusher with air suspension, working toilet, working air conditioner, Webasto hydroponic heater, refigurater, inverter for coffee makers etc. So I am thinking of using as much as possible the technology that is on the bus already. Air suspension can be configured with solenoid valves to work as a leveling system (that has been done). Still wondering why double your air conditioning system with another system?
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Old 04-27-2017, 10:30 PM   #7
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My guess is the type of pump chosen for the A/C system. The A/C system that came on my bus seems to be a piston-style pump thats designed to run at a minimum speed and produce a specific pressure and flow rate with little deviation. I don't think it can run efficiently at a lower speed or pressure because the valves are specifically set for that pressure and flow.

The A/C that can run at lower speeds and pressures (mini- and multi-splits) use a different kind of pump (scroll pump) driven by an AC motor on a variable-frequency inverter and has computer controlled valves. The computer controls the speed of the motor/pump and the valves for a given cooling demand. So I don't think its as easy as it looks.

But I'm just speculating based on what little I know. We'd need an A/C technician to really give us the information.
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Old 04-28-2017, 02:23 AM   #8
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"My guess is the type of pump chosen for the A/C system. The A/C system that came on my bus seems to be a piston-style pump thats designed to run at a minimum speed and produce a specific pressure and flow rate with little deviation. I don't think it can run efficiently at a lower speed or pressure because the valves are specifically set for that pressure and flow."


They are piston compressors. You might be correct that too powerful AC motor would be needed. Those draw 3 times more amps than normal operation while starting also.

This is a thread I could find 12v single shaft motor to run A/C by belt? - DIY Electric Car Forums

There is not much about this topic out there.

My gues is also that bus air conditioning systems are very powerful, the motors needed would be too much (may be 10 kw?).
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Old 04-28-2017, 02:50 AM   #9
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ok, here is one

https://www.transarctic.com/media/co...ygwtmzzb2t.pdf

Revolution range: 600-4000 RPM
Displacement: 635 cubic centimeters/38.75 cubic inches
So they are powerful. You really don't need such a powerful air conditioner on RV.
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Old 04-28-2017, 06:13 AM   #10
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the reason people dont piut an electric motor on the compressor is capacity... if you think of a Coach A/C system, its design is to cool a bus down while moving and full..

a full size school bus like a 12-14 row bluebird will typically be outfiited with 2 A/C systems for a total of 120,000 BTU.. thats right nearly 10 TONS of A/C..

a moving bus is much different to cool than a stationary bus parked in the shade.. you have road heat, wind blowing in the windows, engine heat (esp in an FE or conventional), sunload, plus the desire to drop the temperature of the bus fairly quickly.. just like a car you get in start it up and want cool air.

a little DC electric motor is not going to push a pair of 5 ton compressors.. you may need upwards of 20 HP. (more under heavy load)..

thus a Pony engine was used for busses that needed to idle a lot.. in a full size converted coach 4 or 5 13000 BTU electric roof airs arent uncommon.. and those are fully insulated coaches with less windows.. Plus those coaches have Dashboard /
Driver A/C thats usually 20k BTU on average..

-Christopher
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