More Dometic aircon HP errors

[crayiii]

We have 4 dometic aircon units and one shuts off with a HI PS error every once in a while.

There is good flow. I also hooked a dock hose up to the line and flushed it out. The strainer screen is clean and I’ve cleaned the air filter. I’m also leaving the compartment the compressor is in open so there is good airflow.

The unit blows nice cold air.

Sometimes it will run for days without any issue then it errors on high pressure. I’ll try to restart it and it errors again. Then, I’ll hit the power button and away it goes for hours or days.

It was flushed with barnacle buster last year and has only run for a few months after that.

It is hot here (80-100) and the marina water is about 85. I have the set point set to 76.

Anything else I should check?

[Sailmonkey]

The high pressure switches are known to occasionally go bad

[crayiii]

Originally Posted by Sailmonkey

The high pressure switches are known to occasionally go bad

It looks like the unit would need to be recharged after changing the switch. Is that correct?

[ItDepends]

HP Failures are only caused by insufficient cooling in the condenser. Maybe a bad pressure switch, but this is very rare, and would be very unlikely to give the symptoms you describe.

You say the flow is "good." "Good" is not a number. Get a number.

Collect it in a bucket and calculate how many gallons per hour are flowing and compare this the the manufactuers specification. What might be just fine when seawater temps are in the 70s might not work when they are in the high 80s

If possible, check the temperature of the water coming out of the AC unit. Hopefully you can find a specification for this. If this is above specification, you need more flow.

Lastly, a check for possible fouling of the interior of the condenser: You can do this by hand, but a IR temp meter is more precise: Check the temperature of the line carrying refrigerant out of the condenser. It should be very close to the temperature of the incoming water.

If the refrigerant is still hot coming out of the condenser, there are only three possibilities:
1. water flow is not sufficient. Clean circuit or get bigger pump.
2. the condenser is fouled. Clean it.
3. the condenser is undersized for the incoming seawater temperature. You are stuck...

[Edit]
One more thing I saw once on an owner installed AC unit. The water connections were BACKWARDS. This provided sufficient cooling at low seawater temperatures, but not when they climbed... Worth a quick check as an easy fix...

[Sailmonkey]

Originally Posted by crayiii

It looks like the unit would need to be recharged after changing the switch. Is that correct?

They’re screwed onto a schrader valve (normally) so a small puff is all that escapes.

[Sailmonkey]

Originally Posted by ItDepends

HP Failures are only caused by insufficient cooling in the condenser. Maybe a bad pressure switch, but this is very rare, and would be very unlikely to give the symptoms you describe.

8 out of 10 times I’ve seen the behavior described it was a failings HP switch. The others were attributable to a failing pump trigger.

When the seawater flow is insufficient a repeatable pattern appears.

[crayiii]

The water temp here is actually hitting at and just below 90. The manual does say that at and above 90, we could see these errors.

This unit is on a pump that it servicing two other units and they aren’t getting the error. They also have a bit more flow than this unit so the manifold must be imbalanced.

One other unit that is on its own pump is also running fine.

[GreenWave]

Water temps above 85 will cause all sorts of issues including this error and just generally insufficient cooling. Not too different from land based AC units that usually cannot cool more than 25 degrees below ambient.

[stevec195]

I had the same symptoms and found the problem to be a loose connection on the high pressure switch!

[ItDepends]

If you are pushing the upper boundaries of the allowed seawater temperature, and an imbalance of water flow is giving this unit a bit less cooling I think you have your answer. It fits all the pieces.

It works OK, but is teetering on the edge of too hot. A bit of a longer than normal run, or hiccup in water flow, and it shuts down.

I would not go changing the pressure switch until I was SURE that cooling was sufficient and the exit temperature of the refrigerant was in spec. Even then, I'd probably make sure I was sure and put a gauge set on it before changing parts that are most liking doing exactly what they are supposed to do by shutting the compressor down when it occasionally rises over the max pressure because of the marginal cooling.
.

[Sailmonkey]

Originally Posted by crayiii

The water temp here is actually hitting at and just below 90. The manual does say that at and above 90, we could see these errors.



This unit is on a pump that it servicing two other units and they aren’t getting the error. They also have a bit more flow than this unit so the manifold must be imbalanced.



One other unit that is on its own pump is also running fine.

Ok, now I’ll second what itdepends is saying. With water temp that high, and multiple consumers on the same pump any small restriction in the system cooling circuit can cause this.

If you’re running constantly in really warm growth filled water you might even need to flush every three months of the flow rate is particularly slow through a single unit.

[Squanderbucks]

At my home dock here in south Florida my canal water temp gets to 90F or above each summer. The units will not run as stated in the manual.

Also, I had a pump that would run fine for about 30 minutes and then shut down from over heating reducing the water flow and HP error. New pump fixed the issue.Check the pump temperature with an infrared gun. I keep one onboard as they are about ten bucks and good for checking all sorts of temps on engines, freezers. etc.

My Depth sounders give me the water temp. I have a spare HP switch after one quit a few years ago in my small parts kit.

[Escapaide]

I had a similar problem, turns out it was a loose electrical connection on the high pressure switch. Spade terminal had vibrated loose.