Marine Air Compressor Problem

[geoffschultz]

My boat has been sitting in San Diego since November. At that time the AC was working fine. We just returned and found that the AC wasn't cooling or heating.

I put gauges on the compressor and saw that I wasn't getting any compression. I thought that perhaps that I had a leak, so I vacuumed the system, but found that it held the vacuum overnight. I then recharged and once again saw that I wasn't getting any compression when cooling. I then ran some tests and am quite confused by what I'm seeing.

In cooling mode, I see the low pressure side reading decrease as expected, but I see no pressure increase on the high side. When I put it into reverse cycle heating mode, I see ~115 PSI on the suction side, but there is no pressure decrease on high side as measured at the rotolock valves on the compressor.

The compressor is clearly generating compression as shown by the heating cycle. I'm absolutely stumped as to why I see no changes in pressure at the high pressure rotolock valve. My guess was that somehow or another the condenser loop was clogged, but then you'd expect the pressure reading to be effected one way or the other by the suction side.

Any bright ideas?

Geoff

 

[Bill Roosa]

reverse cycle AC 101

The compressor is always a compressor. So the high side ALWAYS has higher pressure than the low side. The motor does not run backward in heat and forward in cool!!!
So how does it work Bill? glad you asked. The fancy valve in the lines reverses the direction of the fluid so the condenser becomes a evaporator and visa-versa, hot plate becomes cold.
So if you do not see pressure in cold mode that would indicate that the pressure regulating device (there are two types, orifice and valve) is bad. Since you are also getting higher pressure on the "high" (you called it the low) side in heat mode that would mean that it is broken in both directions.
It is located before the (cool mode) evaporator. The place where the line begins to get cold when operating normaly

 

[dwain6805]

Hi Geoff,
Would need a whole lot more info to suggest anything for certain. Like Temps @ suction line, discharge, condenser in & out, evap in & out, ect. R-22 or 410 or 134? If your condenser was plugged either on the seawater side or freon side you'd have a high pressure situation.
Possibilities include a bad TXV or a reversing valve, or compressor valves (not likely), or?
After rereading your post. I think I'd be looking at the reversing valve first. It sounds like (with limited info) it might be stuck, broken, disconnected, or something, and that's allowing gas to bypass though it, and return to the compressor. It's a bit difficult to explain in a short reply but here's a try. the small tube on one side by it's self is the discharge from the compressor and should be warm to hot reguardless of heat or cool. The three larger tubes are on the opposite side and will be like this or reversed. Tube # 1 will be the return/supply to the condenser, Tube #2 will be the return to the compressor, Tube #3 will be the return/supply to the evaporator coil.
In cooling the small tube should be warm, Tube#1 should be warm the same temp as the small line, Tube#2 should be cold, and Tube #3 should be the same as #2. In heat it would be the same, only opposite.
Oh Man, see I knew I couldn't put it in writing! I'll try and attach a diagram of a refrigerant piping for a heat pump, this is a generic diagram and you may not have every thing in it, but it shows the flow.
Possible problems with a RV: wiring (disconnected or broken), burnt out coil, forgien matter jaming the valve (or other problem internal to the valve.
Sorry not much help really.
Dwain

PS Nice boat! I'm in B-37 and admired your boat when I'm over there. I'll be there in a couple of weeks if your still there and need a hand, A/C is what I do on land.

 

[geoffschultz]

I just found out something that I didn't know…that the gauge ports on the Marine Air system have Schroeder valves. My refrigeration system doesn't have Schroeder valves. Anyhow, due to access restrictions, I had reversed the HP hose so that the end with the pin which depresses the Schroeder valve was at the gauge end! Duh…Won't make that mistake again.

Now it's back to taking some real readings and diagnosing this.