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Aux ac unit

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Aux ac unit
Fri Sep 04, 2009 11:06 am

I have been trying to decide what to do with my aux ac unit. I asked chrisber about it and thought that it might be a good idea to share his answer.

I have a welch 26,000 btu aux ac in the back that is belt drive off the engine. I would like to convert it to run on shore power. Do you know what the btu output on the driver ac unit and just how big the motor that runs it is? That might give me an idea of what it would take to run that unit.
Thank you

"I’ll try to answer your question(s) as good as I can.

(1) Welch Industries Auxiliary Air Conditioning systems have been installed on some commercial Eagle coaches in the past to provide “additional cooling” and therefore enhance the comfort for the passengers. Hence, the Welsh A/C systems were designed as “bolt-in accessories” and are totally independent of the main bus A/C system. This way it becomes an excellent back-up unit in case of main system failure making it possible for an operator to continue a trip without interruption even after the main system has failed.

Using shore power as the energy source for the Welsh system would require (a) an electric motor to drive the existing compressor or (b) the incorporation of an electric compressor akin to the ones used within the external condensing unit of a home A/C system (an efficient scroll compressor would be a good choice). In the latter case, you would break open the existing Freon gas lines and re-engineer the overall system and controls, which is certainly a none-trivial task.

Personally, I’d first try to use a 240 VAC electric motor that is typically used on large air compressors to belt-drive your Welsh A/C compressor. The technical challenge here is that you need to figure out the best performance parameter of the A/C compressor as a function of input shaft RPM. This way you can design and implement the appropriate pulley/belt drive ratio as it relates to the fixed RPM of the electric motor.

(2) The driver’s A/C unit of an Eagle 10 has a 1.5 ton capacity (based on the expansion valve type used). A separate A/C compressor is not employed as the Freon loop from the main system is tapped and routed to the driver’s air at the spare tire compartment of the bus.

I am not sure about the Eagle 5 configuration. Yet, I would venture to say that the implementation is similar so that the driver’s air can only be used during travel and the main A/C compressor provides the pressure for the Freon loop. Other than a blower motor providing air flow through the expansion unit up front and through the driver’s compartment, there is no other device used at the frontage of your Eagle.

Best of luck, Chris

"I had been thinking option "a" all along. I think that because of the need for 240v I am going to try to figure out what the unit is worth (i know retail is around $2100), sell it and replace with a pair of smaller 110v mini splits so that I will be able to have more options on how to power the units.

I may need to pick your brain a little more on the subject. I really appreciate the educated yet simple answer. one other thing, any clue why Welch would have told me it was impossible? I thought it sounded like it should work the way you described but for some reason they said it wouldn't."
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Re: Aux ac unit
Sat Sep 05, 2009 6:23 pm

I refuse to recognize the word “impossible,” because I believe you can more often than not find solutions to the most complex problems. All it takes is time, effort and the necessary funding.

Now, there are instances when the simplest way out may not be practical, such as installing a very large 240 VAC single phase motor to belt drive an existing automotive air conditioning compressor at the back end of the bus or trying to regression test and re-engineer an existing system. And certainly, there are -- as you already indicated -- other more elegant solutions to cooling a motor coach that is converted for recreational use only.

Thinking the best for you,
Christian Berlit
El Paso, TX

He who has a why to live can bear almost any how. -- Friedrich Nietzsche
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