A/C Unit as Heat Pump

[Tom and Amanda Lang <rustnrot@domain.elided>]

>Has anyone ever install additional tubing and a reversing valve for an
>automotive  AC systems?  This would give you instant heat out of your AC
>system to aid in heating up the cab before the engine is warm.  
>
>Rob Marks

The colder it gets, the worse this will work.  The heat that untimately
goes into the cab has to come from outside.  Just like home heat pumps that
work great in mildly cold conditions, i.e. above 32 degrees F, once the
outside temp drops below that, the air coming out of the registers is *not*
very hot, that is, until the "auxiliary resistance heating coils" kick in,
simultaneously your electric meter begins to spin wildly  . . .

HVAC mode off.