Low pressure freon alarm

[Mischief Managed]

I get an occasional low pressure Freon alarm on one of my reverse cycle AC units that shuts the system down. It blows ice cold air in AC mode and makes plenty of heat in heat mode. If I wait awhile, the alarm will clear and the unit will start working again autonomously. I can usually just power cycle it and get it to work again within minutes of the alarm if I don't feel like waiting.



I had the freon level (pressure) checked and it was perfect. I have a rudimentary understanding of how these systems work, but not enough to truly troubleshoot. I don't want to start throwing parts at it until I understand it better.



The other two AC units in the boat share the same raw water pump and the manifold is wide open to all three. Could my problem just be inadequate water flow through the affected AC unit? Cleaning the raw water strainer does not seem to make a difference, but maybe the flow through the affected unit is marginal in the best of circumstances... I was thinking about adding flow control valves to the raw water lines in the other two units to see if it helps.


Any thoughts would be appreciated.

 

[Lepke]

Marine growth happens in AC systems, just like engines. I'd flush the raw water system.

 

[Comodave]

Maybe try Barnacle Buster in the water path. Pump it in and let it sit for about 6 hours or so then flush it out.

 

[Barking Sands]

So it is functioning perfect all the way up to the alarm and shut down? If its the low pressure switch tripping it they are usually pretty low...like 6 PSI. Usually that is low servicing, faulty/intermittent pressure switch, or clog in the expansion valve with internal debris (freon system)

When he checked level did he just hook up gauges? You really need to recover the freon by weight to check what amount was in it and then reservice with the correct weight the system calls for.

 

[MacPhid]

Reduced water flow would result in a high pressure alarm. If static and running system pressures are correct I would look at the low pressure switch or relay. We’re the guages attached during a low pressure alarm event?

James

 

[Mischief Managed]

Reduced water flow would result in a high pressure alarm. If static and running system pressures are correct I would look at the low pressure switch or relay. We’re the guages attached during a low pressure alarm event?

James

No, there can be days between alarms and it did not occur while the gauges were attached.

 

[Mischief Managed]

So it is functioning perfect all the way up to the alarm and shut down? If its the low pressure switch tripping it they are usually pretty low...like 6 PSI. Usually that is low servicing, faulty/intermittent pressure switch, or clog in the expansion valve with internal debris (freon system)

When he checked level did he just hook up gauges? You really need to recover the freon by weight to check what amount was in it and then reservice with the correct weight the system calls for.

Yes, seems to work perfectly until the alarm trips and it shuts down.



Freon level was checked solely with gauges.

 

[Mischief Managed]

I will try flushing and I will use Barnacle Buster. Thanks for the suggestions.

 

[gulfstar1]

Intermittent problems can be the most frustrating to diagnose. I had a similar problem with the high pressure switch on my cruisair unit. It finally became frequent enough that I was able to see it trip with gauges connected. It confirmed that the switch was bad. I replaced it and the problem was solved. I'm not saying that is your solution but it could be. You would have to know what the suction pressure is when the unit goes into alarm. Also if you are able you can trace the wiring from the switch to see if there is a loose connection that could cause the issue occasionally. A plugged air filter or dirty coil can also cause low refrigerant pressures.

 

[Mischief Managed]

Intermittent problems can be the most frustrating to diagnose. I had a similar problem with the high pressure switch on my cruisair unit. It finally became frequent enough that I was able to see it trip with gauges connected. It confirmed that the switch was bad. I replaced it and the problem was solved. I'm not saying that is your solution but it could be. You would have to know what the suction pressure is when the unit goes into alarm. Also if you are able you can trace the wiring from the switch to see if there is a loose connection that could cause the issue occasionally. A plugged air filter or dirty coil can also cause low refrigerant pressures.

I will get a set of gauges connected and see if I can catch it in the act next Summer if cleaning the raw water passages does not help. I keep the air filter very clean and cleaning it has not made a difference in the frequency of the problem. Thank you for this idea.