How to turn an air-conditioner into a heat pump (on a 1969 Airstream Trailer)

Picture of How to turn an air-conditioner into a heat pump (on a 1969 Airstream Trailer)
I have a 1969 Airstream Ambassador travel trailer with the original air-conditioner.  I like to upgrade things while keeping them as original as possible.  I decided to rebuild the air-conditioner (new compressor, new fan motor), but while I was at it, I figured I would turn it into a heat pump as well!

A heat pump is just an air-conditioner that can change the path of the refrigerant.  In cool mode, the refrigerant goes from the compressor to the heat exchanger outside the cooled space (condenser), through the capillary tube (or thermal expansion valve, TXV), into the heat exchanger inside the cooled space (evaporator), and then back to the compressor.  In heat mode it goes from the compressor to the heat exchanger inside the heated space (condenser), through the capillary tube (or TXV), into the heat exchanger outside the heated space (evaporator), and then back to the compressor.  Remember, heat flows out of the evaporators and into  condensers.

Here's a link that provides a more detailed explanation: http://www.heatpump-reviews.com/heat-pump.html
This unit uses a capillary tube to restrict refrigerant flow and generate the pressure needed to condense the refrigerant.  Modern units use TXVs to regulate the pressure of system.  While they are more efficient, they generally only work when the refrigerant flows in one direction unless they are specifically designed for heat pumps.  A capillary tube is a long, thin tube that is a specific diameter and length to generate a specific pressure.  There are no mechanical parts in a capillary tube, therefore refrigerant can flow through it in both directions.  So in order to make this A/C a heat pump, I only needed to add a reversing valve and reroute the copper tubing.

Here's what I did:
-Remove unit from roof of trailer.
-Get part numbers of compressor and fan motor to find compatible replacements, if needed.  (I did)
-Measure copper tubing diameter so you can but a compatible reversing valve.  Reversing valves come in different sizes based on how big the unit they are designed for.  Try to find a valve that has the same size fittings as the copper tubing in the A/C unit.  If not, you'll have to get adapters to step up or down sizes.  Remeber, refrigeration copper is "tubing" and is measured on the outside diameter and not "pipe" which is measured on the inside diameter.
tlbdm33 months ago

Did you have to replace your expansion valve to one that would work both directions?

jmpratt (author)  tlbdm33 months ago
No, this unit has a capillary tube instead of an expansion valve. I'd it did, you would have to install one for each direction.
blackghost2 years ago
would an A/C unit work like a heat pump if u installed it in a window backwards ?
so the hot coil would be inside and the cold coil on the outside ......

jmpratt (author)  blackghost2 years ago
Yes. A window A/C unit is a heat pump that moves heat from inside to outside. If you turned it a round, it would pump heat from outside to inside. However, as the outside temperature approaches freezing, the unit's will become unable to transfer heat. Also, the evaporator will probably ice over because there is no auto defrost cycle.
sbharti jmpratt8 months ago

Isn't your H/P unit icing up near freezing temperature?

jmpratt (author)  sbharti8 months ago

I used it in the desert so there wasn't enough moisture to freeze up. If it does, you just need to switch it to A/C mode. That will push heat back into the outside coil and melt the ice. That's what a home heatpump does automatically to keep from freezing the outside coil.

Thanks for the fast reply !
I was thinking icing was going to be a problem. I guess i dont need to test a backwards A/C unit anymore ha
hybridupgrade10 months ago

I have been converting air conditioners to heat pumps for 8 years.You did a good job. I sell a kit for central units. We mostly upgrade the air conditioners that are combined with fossil fuel burning furnaces. I call it hybrid upgrade.

we achieve heating utility bill savings of 30 to 40% and a return on investment of three years. it makes the a/c more efficient as well.


jmpratt (author)  hybridupgrade10 months ago
Thanks! Your hybrid system looks pretty good as well.