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. 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.  polar wind air conditioning unitA capillary tube is a long, thin tube that is a specific diameter and length to generate a specific pressure.  how to charge ac unit with 410aThere are no mechanical parts in a capillary tube, therefore refrigerant can flow through it in both directions.  18000 btu window air conditioner heatSo 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.  

-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. Step 1: Install the piecesShow All Items« PreviousNext »View All Steps DownloadHow Can B-Y Help? Have B-Y contact you Why Are You Adjusting That TXV? Why are you adjusting that TXV? To answer this question we first need to look at the main functions of the TXV. The TXV is designed to keep the evaporator as full of saturated refrigerant as possible while at the same time protecting the compressor from slugging or overheating. This is accomplished by maintaining a set superheat. The typical TXV comes factory set for 8-12 degrees of evaporator superheat, which in most cases should be fine.

What is the correct setting for evaporator superheat? While it is true lower superheat will make the evaporator more efficient, we need to be more concerned with compressor or total superheat. If we check the superheat on the suction line 6” from the compressor we should normally have at least 20 degrees of total superheat. This will ensure the compressor is not slugging with liquid even when frost is present. The suction line temperature at the compressor should not exceed 65 degrees to ensure proper compressor cooling. The last but most important reading is the discharge line temperature taken 6” from the compressor. This temperature should never exceed 220 degrees, as higher discharge temperatures will lead to compressor failures. Reducing superheat will lower both the compressor suction line and discharge line temperatures. The TXV can not be adjusted open or closed, it is a modulating valve. Turning the adjustment stem clockwise will only increase spring pressure causing a higher superheat.

Turning the adjustment stem counterclockwise will decrease spring pressure reducing superheat. When an operating refrigeration system stops working, the TXV may have lost its power head charge or it may have become restricted, but it’s not likely that it came out of adjustment. Clean or replace the malfunctioning valve, don’t try to readjust it. When replacing a TXV, protect it from overheating while brazing as this will damage the new valve. The sensing bulb should be mounted snuggly to the suction line on the evaporator outlet at the 9:00 or 3:00 position for smaller suction lines 5/8 or less. For suction lines 7/8 and larger the bulb should be mounted at the 4:00 or 8:00 position. Adjustments may be needed on a new system at start up, especially when you have long line runs. Crankcase Pressure RegulatorMini-SplitA/C Compressors You know how when you change the filter in your air conditioner, it has a little arrow on the edge showing which way the air is supposed to flow through it?

What do you think happens if you put it in with the arrow in the wrong direction? And then let it get too dirty? That's what happened with the filter below. Notice that it's dirty. Notice also that it seems to be a bit lighter in color in the center. Looking at it from the side (above), you can see that the filter material is blown out. The blower in the air conditioner was trying really hard to pull air through the filter but the static pressure across it was high because of the dirt. Looking at the other side of the filter, you can see the wire mesh is now separated from the filter fabric. Of course, now it's clear why that wire mesh is there in the first place. It holds the filter fabric in place to keep it from getting sucked into the blower. What happened here is that the air conditioner pulled so hard on that filter that it sucked big chunks of the dirt and fabric off of the filter. Then it deposited them on the evaporator coil. A while back I wrote about a dirty evaporator coil, and that one had a large accumulation of small stuff.