Powering Coach AC While Engine is Off

[brettpearson67]

Was wondering if anyone has tried running coach ac with another compessor(electric) while engine is off?

[richard5933]

Seems like running the huge HVAC air handler fan would use as much or more power than the compressor.

[Jim Blackwood]

It's a DC motor so if you want to run it slower just supply less voltage.

Jim

[brettpearson67]

I'm picking up a DL3 this week and thought that there might be a way to switch to an electric compessor while parked, rather than replace it with rooftops or minsplits or basement hvac. Especially since it is still working great.
Maybe even some sort of ac motor powering the coach compressor? Is there such a thing as a "dual fuel" compressor, so to speak?

[rusty]

The only eagle 25 built had an AC system like that. The last time I saw it at the poor excuse for a factory it was working. I have not seen the bus or have heard if the system is working. I don't know what size the system was.
Wayne

[brettpearson67]

It seems like the coach compressor is maybe 16-18 tons. HP requirements of 12-14. doable with a 240 volt power supply. Although I dont know that the requirements wouldn't be less for an electric motor, as torque specs are different?

[Jim Blackwood]

I didn't know anybody had done it but that is my plan eventually. I don't think it is too practical to try to drive the original compressor with an electric motor, both because newer sealed compressors are more efficient and because the drive would likely be both impractical and inefficient. But there is no reason a sealed compressor could not be plumbed in parallel to the original. What size to use is the question. My thought was that you might be able to get by with running two smaller sealed compressors, making it more versatile for if you had 30 or 50 amp service. Run one or both depending on power available.

Jim

[brettpearson67]

I’m waiting for my HVAC friend to get back to me to talk about sizing the compressor/s

[Jim Blackwood]

It will be interesting to see what he has to say.

Jim

[jap42]

So this was one of my first thoughts also. I asked on an HVAC form I belong to about running a electric compressor in parallel.

As I understand the OTR HVAC system is much larger then typically required because its harder to heat or cool the bus while its in motion. So I want to know, how big is the system now, and could a smaller compressor providing 24K-36K be feasible using the same condenser and evap.

One Idea I had was to replace the current belt driven compressor with an A/C generator. 240V 10KW. And then use the existing system with a 240V compressor and fans.

[chessie4905]

You could consider one of these run by an electric motor. GM used two of these in 4905's as an option inplace of the big V york compressor. Might need a large motor though. You also will need lots of current to run the condenser fan and blower motors.
https://www.hemmings.com/stories/article/frigidaire-a-6-air-conditioning-compressor

[Jim Blackwood]

Maybe you could use a couple of these:

https://ordering.fwwebb.com/woitem/437290*1?CAWELAID&gclid=CjwKCAjw8df2BRA3EiwAvfZWaMuXio9wJ7zPZet5FrsR6i5beX37E8xLPLwtLEhZ90JTL5cet5XqjBoC3UsQAvD_BwE

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Or, depending on the current demands, maybe two or three 3 ton units and stage them in as needed, leave the engine driven compressor alone, and use it OTR as intended. They do have intake and exhaust valves that will prevent backflow. (Might need check valves with the scroll compressors.)

The 102DL3 has 13 tons of on board air at least. Depending on how you add it up, it could be as much as 14 tons.

Jim

[Fred Mc]

Seems to me that it MIGHT be more cost effective and easier to simply put in a mini split.
The Bus Grease Monkey has replaced both his rooftops with a single min split that he says can cool his bus to the point of being uncomfortably cold. AND he runs his off batteries.

[Jim Blackwood]

There is nothing magical about a mini-split other than the new ones using the more efficient type of compressors. Fans being fans and motors being motors, there is a limit as to what is to be gained by changing the air movers. Yes the OTR units are large but it doesn't mean they have to be run at full speed. Their efficiency at lower speeds may be less... or it may not. And, pwm drives are available cheap to boost the efficiency.

What we really want to know is how many amps does it take to start and how many to run a given size compressor in terms of amps per btu. The lower that ratio is, the higher cooling we can achieve from a given shore line. It is likely that ratio is rather closely tied to seer rating, and seer ratings have gone up dramatically in the last 20 years. So the first thing is to upgrade the compressor. The largest one that the shore line will support should be the objective here but soft-start will prove a clear advantage, possibly dropping the amperage draw to the point that is is only necessary to delay the air fans until the compressor is up to speed to even out the current draw and leave some margin.

Jim

[buswarrior]

The huge elephant in the room, is WASTED HVAC...

The mini-splits have rapidly proven that roof airs are total garbage and lies, when it comes down to the effect of their operation on the inside temp.

Up in that box on the roof is some very sad chunks of cheap white styrofoam, poor attention to heat/cold transfer between inside/outside and the heat producing parts. The cold is being stolen up in the box.

Sure, the PARTS may be 12k worth of cooling, but an RV never gets anywhere near 12k of cooling down below.

The minisplit keeps all the hot outside, and all the cold inside, so the effective "cold" out of parts that are rated at the same 12k, is much better.

The elephant in the room for using the stock HVAC is air intrusion, and having to keep cool all those surfaces of the air distribution system, that don't contribute to interior cooling.

Grease Monkey isn't the source i would be using for my information.

Happy coaching!
Buswarrior