On Becoming a Refrigeration Tech

As I mentioned previously, and you may have read, Eolian's heat pump quit working due to lack of Freon.

Never fearing to tackle a new field, I ordered a 5 lb container of R-410a refrigerant and a syringe of leak-stop fluid compatible with R-410a.  Gonna find out if I can be a refrigeration tech...

Before I begin, some basics that I may have discussed before.

Here's how a heat pump works:

• A compressor pressurizes Freon vapor.  This heats it up (feel that bicycle pump after blowing up your tire...)
• The hot Freon vapor is passed thru a heat exchanger where it gives up its heat to the cabin air, and condenses to a liquid as it is cooled.  
• The liquid passes thru a narrow orifice and is allowed to expand into a low pressure space (created by the inlet of the compressor).  This cools it down really cold.  
• The cold gas is heated up in another heat exchanger , getting heat from sea water.
• The re-warmed vapor enters the compressor inlet, and the cycle repeats.

Thus, the system extracts heat from sea water and delivers it to the cabin.

The problem aboard Eolian was that almost all of the Freon had leaked from the system, meaning that there was essentially 0 psi at the compressor inlet when the compressor was running.  With our current water temperature, the inlet pressure should have been around 100 psi.  Outlet pressure should have been 400 psi, but was only 200 psi.  When the compressor was not running, the system pressure was 150 psi, meaning that it was unlikely that any significant amounts of air or moisture had leaked in.

Clearly there was a leak - otherwise the Freon would still be in there.  Thus the reason I ordered some leak-stop.  This came as a blue liquid in a big fat syringe, with fittings to attach it to the low pressure tap in the system.

Here's what we did:

1. Inject the leak stop:  Jane started the system, the inlet pressure fell to 0, and I injected the leak stop against the lack of backpressure.  I disconnected and Jane stopped the system.
2. Hook up the Freon cylinder to the inlet port.  Jane starts the system again and the inlet pressure falls toward zero once again.  I turn the Freon cylinder over so that the outlet is on the bottom, meaning I will be injecting liquid.  I open the valve, briefly, and a shot of liquid Freon enters the system.  Inlet pressure rises briefly, and then falls again as the injected Freon evaporates and goes into circulation.
3. Continue injecting bursts of Freon until the inlet pressure comes up to 100 psi.

Ta Da!  The heat pump is delivering hot air!

Too much is not good

But:  overnight, as the system cycled on and off maintaining out nighttime temp of 63 degrees, I noticed that the compressor was making an uncomfortable noise when starting up.  I assumed that I had over-charged the system, and the the compressor was inhaling a little liquid on startup.

A real refrigeration tech would have evacuated the system with a vacuum pump, and then charged it with *exactly* 1.45 lb of Freon. But I have no vacuum pump and no scale.

So I had charged until I showed the desired pressure on the compressor inlet, but I failed to look at the compressor outlet - it was nearly 450 psi. It should have been a little less than 400 psi. Aside from damaging the compressor by feeding it liquid, too much Freon in the system also meant that the condenser and evaporator would be flooded with liquid, reducing the capacity of the system to transfer heat.

I bled it down until the high pressure side read 400 psi.  Everything seems to be fine now.  Now the only question remaining is whether the leak-stop stopped the leak...  Time will tell.

On Becoming a Refrigeration Tech