[BradC]

Ok, some practical experience.

In Australia we don't have "heat pumps" (we do, but we call them reverse cycle air conditioners).

I have 2 Window A/C units (both reverse cycle) and my car A/C running on R290.

The car A/C is actually running a 60/40 mix of Propane and Iso-Butane (pressures are close to R12).

Both window A/C units are running on straight Propane.

I've not taken detailed measurements, therefore my evidence is strictly anecdotal. Both window A/C units run as well on R290 as they did on R22. I changed them over for the "because I can" factor, not because they needed it.

I removed the R22 by using a thermal vacuum. I vacced out a propane bottle down to about 200 microns. I then placed it in an esky (cooler, chilly-bin..) packed with dry ice and filled with methylated spirits (denatured alcohol). I did this as the vapor pressure of R22 at ~-70 Degrees C is below atmospheric an therefore it would reliably suck all the R22 out of the system (and I did not own a recovery machine back then).

I then charged the systems up with nitrogen, cut the end of the process tube off and brazed on schraders.

Both systems were charged loosely by monitoring the suction line temp where it leaves the evap (in cooling mode) with my calibrated finger and charging them up until it was "about right". Both systems have done in excess of 18 months service and are going strong. I did not filter or otherwise modify the straight BBQ propane I fed into them.

Since then, I've obtained a couple of proper recovery tank Y-valves and put them in some locally obtained propane tanks. I've also bought a recovery machine and some other assorted fruit to allow me to recirculate propane through a filter and sight glass to clean it up proir to feeding it into my ducted A/C which is sitting in the garage to be installed next weekend.

If you are mixing up gas for your car, you want iso-butane not butane. I went and bought one of every kind of camping gas disposable cylinder I could get my hands on, put them all in the freezer and then measured the pressure at the valve output. Iso-Butane retains higher pressure at 0 Degrees than Butane so it's easy to see which is which.

I then dumped 4 cans into an empty (vacced to 200 microns) propane cylinder and then weighed in the propane on top of that. You need to give the bottle a good shake and roll before you charge it in, and you need to charge it in as a liquid to prevent it fractioning off as it evaporates. I used my gauge set as an expansion valve to dump liquid from the bottle, but charge it into the system as a vapor. The gauges get *really* cold.

There.. now the thread has some real experience.

Hopefully after next weekend, when I hook up my new 7KW ducted system I'll have some more to post.

<edit> Charging scales are REALLY handy. I found some *cheap* shop scales on e-bay that do 30kg with a resolution of 5g. They were about $35 delivered and have a rechargable battery in them. Brilliant for mixing gasses and weighing in and out charges.