Marine Air(dometic) passport II AC compressor cycling

[phorvati]

I am experiencing compressor shutting off at random times during cooling cycle. Then it comes back after few minutes.

No errors are displayed on the control panel. I don't have HHH which would come if water strainer is clogged or air intake screen is blocked.
I cleaned both just now and compressor still exhibits this behavior.
I went through the U modes(programming modes)
U10 was air fan. Default is run fan all the time (1). I changed that to cycle fan with compressor. (0) I did this because it was hard to tell when compressor is doing the shot-off behavior. I would have to go out to look for water coming out.

I am pretty sure the programmed setting "stuck" because i went back and checked.

Interestingly when compressor shuts off fan still runs. Perhaps that might be a clue.

When compressor shuts off, water pump shuts off as well. So i am wondering what to check next or is this behavior normal?


What concerns me is that on one occasion, as compressor tried to start back up, there was significant AC draw(amp meter was pegging to full scale) on 50A analog AC mains (120V) meter panel.



U6 fail safe mode and mnemonics is set to 3. Which i am assuming would cause the system to display the fail code.

[Richard Kollmann]

This could be cooling water not removing the heat, check the condenser's temperature by putting your hand on it. If the larger tube is too hot to keep had on there is ether scale in system or water flow is restricted. Your high amperage is also indication cooling water trouble. The high pressure switch is causing the cycling without this switch or if it fails there can be a major failure.

[phorvati]

So for some reason its not happening any more. I poked around a bit, top of compressor is at 140F on IR gun, dryer and large condenser lines are cool, moisture on them. small line(discharge) is too hot to touch. That should be normal. I did have raw water flow issues before, as in even after cleaning the strainer, pump was not pumping good flow, only trickle. But then it started working again. At that time in anticipation of potential issues i bought a rebuild kit for the raw water pump. I might do that maintenance work now.
https://marinepartssource.com/500-gp...0130-0115-0200

[phorvati]

So this intermittent problem did come back. Inadvertently, While cleaning the bottom of the boat yesterday, I noticed that raw water through hole for AC intake, when looking at it from under the boat, had a lot of hard barnacles on the inside wall. So I used a flat head screw driver to chop up as much of it and let the barnacles fall out. After that, I ran AC for few hours without an issue. Given that days are getting colder in RI its hardly a full test but i hope that was the main contributor to my behavior.

It was hard to tell based on water coming out of the hull how much i might have improved the sea water flow and subsequent heat exchange.

[phorvati]

Originally Posted by Richard Kollmann

This could be cooling water not removing the heat, check the condenser's temperature by putting your hand on it. If the larger tube is too hot to keep had on there is ether scale in system or water flow is restricted. Your high amperage is also indication cooling water trouble. The high pressure switch is causing the cycling without this switch or if it fails there can be a major failure.

Its hot in RI and I am getting back that intermittent shutdown problem. If my seawater flow is good, it filled up a 5 gal bucket in 1 minute. could I still have an issue with transfer of heat?

If I take all my wife's clothing out of the closet where unit is located, and i open the doors, it helps system run longer before shutdowns. This leads me to thing that heat is making high pressure switch open.

Does anyone know at what PSI high pressure switch opens on Marine Air(dometic) passport II AC?
There is a high pressure service port right next to the switch, and i was going to put my gauge set just to see what i get for pressure when system shuts down.

[sailormed]

There is a short pause programmed in the software of these units. Apparently it is in order to avoid the freezing of the cooling fins. Our AC (SMXir control unit) has been showing this behavior for the last 10 years.

[GreenWave]

With good flow YES you could still have a heat transfer problem. Two possible causes. First, is when the sea water temp is very high. On my MarineAire it emphatically states that above 90 F is no good. Guess how hot the bay is this week?
Second possible cause is air flow, or lack thereof. So blockage, dirt on condensor etc.

[Sailmonkey]

Originally Posted by GreenWave

With good flow YES you could still have a heat transfer problem. Two possible causes. First, is when the sea water temp is very high. On my MarineAire it emphatically states that above 90 F is no good. Guess how hot the bay is this week?
Second possible cause is air flow, or lack thereof. So blockage, dirt on condensor etc.

Scale in the condenser coils also cause poor heat transfer.

[GreenWave]

Originally Posted by Sailmonkey

Scale in the condenser coils also cause poor heat transfer.

IN or ON the condenser coils? Just how does one address that problem? Do you mean scale inside the water loop that could be treated with something like Barnacle Buster?

[Sailmonkey]

Originally Posted by GreenWave

IN or ON the condenser coils? Just how does one address that problem? Do you mean scale inside the water loop that could be treated with something like Barnacle Buster?

Yes, the “water coil” is the condenser. When the interior of the condenser coil is even lightly scaled heat transfer suffers.

[phorvati]

Seawater is ~70F in RI. But air flow blockage is the next thing I look into. Air flow must be cooling the compressor itself. When I got the clothing out of the closet and opened the doors, it helped run longer between shut downs.

But I also cant help but wonder if wiring in high pressure switch has intermittent continuity issue. Because one time I wiggled the wires a bit and compressor kicked right back in. Might have been coincidental.

[GreenWave]

Originally Posted by phorvati

Seawater is ~70F in RI. But air flow blockage is the next thing I look into. Air flow must be cooling the compressor itself. When I got the clothing out of the closet and opened the doors, it helped run longer between shut downs.

But I also cant help but wonder if wiring in high pressure switch has intermittent continuity issue. Because one time I wiggled the wires a bit and compressor kicked right back in. Might have been coincidental.

You know what they say - always look at the simplest fixes first. And for boats and power/electrical that starts with the connections

[phorvati]

My high pressure is at 215PSI for high side. That sounds normal for R22. So its either air flow or wires of high pressure switch. But I am yet to witness it cutting out with gauge there to confirm pressure dint rise suddenly.

[Bowdrie]

Those who have posted about scale buildup in the condenser may very well be on to something.
IIRC, the condenser in your system was manufactured by "Packless" and can be identified as to model/part#.
If you can measure the temps of the inlet and outlet on the Freon side of the circuit, you'll get the Delta.
Packless has charts that show for a given water flow/water temp, what the temp drop should be across the condenser.
Also, measuring the water temps across the inlet/outlet of the condenser will get a "ballpark" idea of the BTUs being absorbed by the water.
From your description of the critters in the thru hull you may well have a heat transfer problem in the coil.
Blocked air flow is not helping matters.
Oh, has anybody "serviced" the unit?
If so, might a serviceman have overcharged the unit?

[Bowdrie]

Sorry to get off on a math tangent in above post.
A previous post mentioned doing the easy things first.
Your system has a pump which is rated for a certain flow.
Take the outlet hose off of the exit thru hull and stick it in a bucket, then by jumpering the pump run it for one minute and see what the actual flow is.
If flow is substantially below spec, now you've something to go on without a lot of expended effort.
If you've access to dock water, you might try hooking up your garden hose directly to the condenser and try that out.
Just thinking out loud,,,,,