Heat Pumps

[Joe Cannarozzi]

I have been told that the reason the heat pumps are set not to function below 40 degrees is due to the fact that freon does not flow very good below that point.

If this is true then could someone explain why it is that every car with factory A/C is designed for the A/C to cycle in the winter with the defrost on with evidently no adverse effect from cycling the freon below 40 degrees??????????

[Jerry Winchester]

Joe,

I don't think it is a freon problem, I think it is a thermodynamics problem in that there isn't enough heat to draw out of the air relative to the delta T needed to efficiently operate the refrigeration cycle. No liquid expansion to gas means no heat.

[dalej]

Jerry, I'm impressed!

[Joe Cannarozzi]

Thank you Jerry. That leads me to my next question.

We have OTR A/C and the switch for the control is a 3 position rocker switch. Off is in the middle, up is A/C, down is heat.

When we purchased our bus the fellow that ran through things with me suggested that in the winter when needing heat not to put the switch in heat but always in the A/C position and with the thermostat set warm it will in fact give heat and the windows will stay defrosted better in this position.

I never practiced this because I was concerned of doing harm to the A/C compressor but I guess from what I now know this is probably a better way to go.?????

[Jim_Scoggins]

Joe:
Thanks for the info.

Quote
When we purchased our bus the fellow that ran through things with me suggested that in the winter when needing heat not to put the switch in heat but always in the A/C position and with the thermostat set warm it will in fact give heat and the windows will stay defrosted better in this position.
End Quote

I haven't really thought about it but that sounds like a good to know item that could be used selectively. I do believe that the OTR compressor running just to heat the coach would result in more, and in most cases, unecessarily increased fuel consumption. I will use it for those early launches then switch back to heat only.

Good tip.

A thinky. The other morning I was running a cruise air just puttering around trying to figure some things out about it. It was around 35 degrees out side. The cruise air was putting out warm air. Do some of these units have an additional heat element in them?

[Just Plain Jeff]

A 'thinky?' From a Marine? Hmmm.

Anyway, here's 2 cents worth. In a camper, you have two types of heat from your A/C units: Heat sticks (very rare in a Prevert conversion) and heat pumps.

Heat pumps actually run the A/C units 'backwards,' and are designed to do just that. If you have a cruise air with SMX, you can go to the front of the POG site and download or look at the SMX control manual for heat pump operation. If you have roof airs, usually there is a setting on the thermostat which will invoke the heat exchanger.

Depending upon your altitute and ambient air temperature/humidity, a heat pump is good to go at between 28-35F, assuming a fully-charged and in good condition unit (clean those A/C filters troops).

Air conditioners with heat pumps like to blow hot air. Wait a minute....ah....anyway, you get it.

The alternative to using heat pumps is, well, y'know.