View Full Version : Dual mode Air Conditioner for RV

15-07-2007, 07:59 AM
Has anyone out there done work around making a dual mode automotive air conditioner. I have always thought it would be great to have an A/C unit that could use the compressor driven by the engine or an electric compressor powered by a shore line connection. This would be used in an RV and keep from having all the redundancy of several A/C units. I am an automotive A/C Tech. and understand the operation of a system but know little about the actual engineering. Do you think such an idea is possible? If not why. Has it already been done and if so by whom.

15-07-2007, 09:48 PM
Hi TKC and welcome to the forum.

Sorry to ask but.... what is a dual mode unit?

15-07-2007, 10:35 PM
Don't know that it exist. Didn't know what else to call it but I am exploring the idea of being able to run an automotive air conditioner with a electric compressor.
Here the picture. You parked in your RV engine off. You have access to 110 volts AC. Is it, could it be possible to use the automotive evaporator, condenser and controls with a electric compressor. Dual mode in that it would have two compressors. One driven by the engine and the other would run on electricity. I hope this helps you understand what I'm hoping to do. I need to lean on the experience of those who have a great deal more refrigeration know how that I do. Bleed on this and let me know if I'm entertaining a lost cause.

16-07-2007, 04:41 AM
Hi tkc

I work on refrigeration and air conditioning on sailboats and have seen many combinations such similar to your proposal.
However, it is usually used for refrigeration rather than air conditioning.
There is often an engine driven compressor identical to those on automobile air conditioners with an air or water cooled condenser and a cold plate evaporator. When the boat is in a marina, where shore power is available, that same cold plate is cooled by a separate hermetic compressor using a separate evaporator coil in the cold plate.
The only sucessful system I have seen using the same refrigerant circuit with both an engine driven compressor and an alternating current driven compressor, had to have an oil management system. It seems that otherwise all of the oil ends up in one compressor and the other one burns out.

16-07-2007, 06:29 AM
Thanks for the reply Mayball
I felt fairly certain that what I was proposing had been done I just didn't know how.
Do you know where I could get additional information on these systems. I would be particularly interested in the system with the oil management system. Do these other units you mentioned share a condenser or are they in reality two complete cooling units sharing the same housing?

16-07-2007, 04:18 PM
I'm sure something could be added with a little bit of cunning :)

I seen quiet a few systems that use engine drive compressor and an overnight compressor, Both compressor use same evaporators and condensers and most of the wiring is the same as well, just on the overnight 'mode' a transformer is used instead of vehicle battery to supply fans/controls.

Oil concerns, can't say too much on that one as I still wonder myself, some units have no oil control at all, some have oil separators, some of both types go on for years and years, some die early. I think if I had such a project I'd fit separators and just make sure they be clean every year when the driers replaced.

I could probably draw up a basic system if you get stuck for info, it's nothing official, couple ideas maybe.
Good luck, sounds a rather interesting project!

16-07-2007, 06:26 PM
This is the best news I have received yet Alpha. Thanks.
I am really hoping that this has if fact been done before because I don't want to do all the figuring, guessing and testing that it would take to get a system up and running. Sounds like the systems you were refering to is on over the road trucks am I correct in assuming that? I need more information to go with on this. Are they OEM, after market or custom fabrications. Give me some leads as to where I might start looking for information. I can picture what the system would look like all except for this oil management system. This is not something I have encountered on automotive air conditioning. Unless the receiver dryer serves this function. Oil management, matching up two compressors, and working with a refrigerant compatible to both compressors these are the questions I am hoping to find answers to.
Once again thanks!

16-07-2007, 06:54 PM
One idea I have is to add an electric motor with a separate clutched drive to the existing compressor.

It would require some modification to the compressor pulley system but might be possible.

17-07-2007, 02:33 AM
I would think oil management would be especially critical on a swash plate compressor similar to the Sandens found on many automobile AC systems, because they have such small oil sumps. Both compressors would need an oil separator followed by a check valve. The separated oil would be routed to the respective suction sides. You might check on the Temprite 320 and 340 series separators at

17-07-2007, 02:50 AM
Has anyone out there done work around making a dual mode automotive air conditioner. .

Have a look at this site.


They produce exactly the kind of thing you are looking for and their site may be of help to you.

Delivery vans in the UK use dual systems all the time. engine driven comp while on the road and mains driven comp while plugged in.
Cheers taz.

18-07-2007, 02:06 PM
One idea I have is to add an electric motor with a separate clutched drive to the existing compressor.

It would require some modification to the compressor pulley system but might be possible.

Brians idea sounds best - using one compressor but two drive mechanisms. This will take up less room - take a look at electric and "dog" clutches to disengage the drive from the engine and engage the electric drive.

Use one switch to disengage one and engage the other - stick in a confirmation circuit that both have occured and also put a timed delay on startup of the electric motor to allow completion of this mechanical process. When reversing this (going back to engine drive) unsure that electric motor has time to stop before it is disengaged and the engine drive is engaged.
Once again put in a confirmation circuit on this re-engagement and a stop circuit on the engine being started until engagement is complete (I would put this at the starter motor solenoid).

Sounds complicated but broken down into each stage it should provide little problems.



18-07-2007, 10:36 PM
another solution is to fit an automotive type compressor on the engine and another one in the top housing of your a/c, some examples of this type of setup include the thermo king v range, the carrier xarios range and the transfrig kv range. all of these have a sanden compressor fitted on the engine of the vehicle and another fitted in the top housing. the compressors used in the top section vary from unit to unit but it will give you an overall idea of a dual unit.

REMEMBER: oil seperators is a must, as was earlier stated, the one compressor will starve of oil and die a horrible death while the other one will be flodded with oil and cause damage as well.


20-07-2007, 05:23 AM
Thanks to everyone for your assistance.
I wrote Alan at Hubbard and lets see what kind of information he is willing to part with. They do in fact make a unit that works on what they call a stand by electrical compressor.
Does anyone else know of a company that is making a similar unit.
So let see what we are up against.
Choosing a compressor. It must run on 120 volts AC with a maximum running current draw of about 10 amps. I would think the capacity of the pump should be nearly the same as that of the engine driven compressor. Thought I'm not sure if that would be necessary as the thermal load on an RV setting is not as great as one with the engine running. The refrigerant and oil must be compatible with both compressors and functional in an automotive environment. What is everyones thoughts on a compressor.

25-07-2007, 08:57 PM
on the thermo king v range units you have a sanden compressor mounted on the engine, its usually a 7h15, and then also a sanden at the top, but a smaller one, like a 7h13 driven by a 1hp electric motor. this could aslo be usefull