Air conditioner

[Oznog]

I have a camper van with a home air conditioning unit installed in the rear window. It is very handy when camping where there is power.

I have a huge ass Solar inverter, around 160 amp alternator, and excellent power cables and terminals installed. That setup can run the a/c unit off of the alternator when stopped just fine. I checked and the battery is still charging and the inverter does not get really hot.

That should be nice because with Texas summers the van's automotive a/c system can't get that thing cold. It's not lethal but not exactly cold either, feels like 80-85F at the driver's seat. Any kind of boost would be great.

The problem is every time I try to drive with this thing it ends up shut down after maybe 10 min and I'm not sure why. I need to check the power inverter further for one. But aside from that, do home a/c systems have any known reason why they can't be used that way? For some reason they usually use R22 instead of R134a- anything funky there, like foaming up when it's shaken around on the road? None of those a/c use some kind of tilt switch or anything like that, do they?

 

[dingo]

I am guessing that the power is ok going to the unit although I wouldn't rule that out at the momnent with what you have discribed.

IF the power is ok then you would be beter taking this to an air-cond forum as it sounds mechanical to me. Having said that I can offer some ideas on what might be the problem.

I take it the unit only shuts down while you are moving. It could be that you are getting too much air flow to the condensor (air cooled fins a the back) or not enough due to the slip stream. You could work this out by looking at how fast you are going when the unit shuts down. AC units depend on a set range of pressures (heat and state of the gas) to work, going outside these ranges will cause the unit to trip out on high or low head pressure.

The other thing that may be happening is that as the unit was not designed to be moved around it may be using gravity as part of the design and by bumping it about causing gas in liquid form to enter the compressor. Without looking at test guages on the unit when it trips out you can only guess.

I would speak to the manufacters of the unit otherwise buy one more suited for what you need, maybe a unit designed for a boat.

 

[Dialtone]

If you take a look at AC units mounted in RV's and Camper trailers, they are just like any window AC unit except the mounting system. They are made for a thru-roof mount setup. They also have ducted shell covers that help airflow when in motion.
If yours is mounted in a rear door window, my bet is that the unit is going into thermal overload when moving due to the lack of airflow thru the exterior coils. That wimpy little fan just cannot circulate the air properly when moving due to the vortex created by the square back of the van.
A possible fix:
I have seen air deflectors for vans & pick-up camper shells that are designed to break up the vortex.
They are basically a wing that is mounted on the top at the rear that forces the air to sweep downward off the trailing edge of the van. They mainly help keep the back glass clear of dust/dirt which would be sucked onto the surface, and also help somewhat to reduce the drag induced by the vortex.

Dialtone

 

[Oznog]

If yours is mounted in a rear door window, my bet is that the unit is going into thermal overload when moving due to the lack of airflow thru the exterior coils. That wimpy little fan just cannot circulate the air properly when moving due to the vortex created by the square back of the van.

That's not a bad theory. I should check if speed makes a difference. I might be able to put a thermistor on the condensor too.
But the vortex would only matter if it cancels out the motion of the fan without so much counterflow that it provides cooling again, just not in the intended airflow direction. The static pressure drop is quite low- fraction of a PSI- so the reduction in dissipation coefficients due to lower density air is going to be minimal.

The idea of liquid hitting the compressor is a good one. Trying to compress a piston full of liquid would probably mean the motor will draw enough current to shut down the inverter resulting in a motor stall. But I listened for the tone the inverter makes during an overload and never heard it once. Nor was a fuse blown inside the A/C unit.

I'm thinking about something I saw where I couldn't get the inverter to work after trying this. I'm not sure what I saw because I fiddled with it, couldn't get it to light its AC ON led, then fiddled some more and the light was on. That's implying to me the inverter is just overheating, but when I idled it parked I didn't see anything like that. In fact, while the inverter was certainly warm it was not really hot to the touch. But then again that was when it was parked in the shade and already fairly cool inside, in contrast to pulling out of a parking lot with it already like 120F inside.

 

[Dean Huster]

They also have ducted shell covers that help airflow when in motion.

Using those systems while on the road was an afterthought. The Coleman A/C units have been designed like that for travel trailers from the beginning. They were on the RVs before some idiot decided that 120VAC generators in campgrounds was a good idea (I wish they would all explode). So, the guys with motorhomes started running their AC generators while they were driving down the road so they could have whole-house A/C ... which implies folks are moving around in the RV while on the road and endangering their lives in case of accident.

As mentioned, one A/C system is just like another. Your car doesn't have A/C problems from the motion, so I'd also assume improper airflow if the electrics are all in order.

Dean