New AC unit acting like old unit, High Pressure Error

[The Brockerts]

Now this new unit has me thinking since it acting just like the old unit.

The unit high pressures out after a little while no matter what the water flow is. I can adjust the water flow from 3-10 gallons per min. Factor recommends 4.5 gallon per min.

The unit is under the front V berth with large intake on the side of the bed.

I'm thinking that it's not pulling all the air across the coils since the unit is just sitting in a large open space with the air opening(and filter) 2 feet away.

So do you think I should box up the intake and direct it to the front of coils?

The Brockerts

 

[rslifkin]

How hot is the water the unit is picking up?

 

[The Brockerts]

88 degrees in 93 out, I've got 3 units running on the same pump, all new(1 or 2 years old), all dometic, and this unit is the same as another unit that runs the same water, at the same flow rate and never HP's out

The Brockerts

 

[O C Diver]

Generally, if it's not getting enough air flow, the evaporator coils ice up. If there's no ice on the coils and fins, it got enough air flow. Have you ever cleaned the condenser tube? Growth forming on the inside of the tube acts like insulation, irrespective of water volume. I know you said it was new, but is it 2 or more years old? Might be worth cycling Barnacle Buster through the condenser tube for a couple of hours.

Ted

 

[twistedtree]

You say that the same pump serves three ac units? This is pretty common from what I’ve seen, but it depends on getting more or less balanced flow through all three branches. My first suspicion would be that there is some restriction in the water line branch to the unit in question such that it’s getting inadequate flow even thought the pump is moving enough water. Are there manifolds or just tee fittings to break out the water flow to each AC unit?

 

[The Brockerts]

This unit is 20 days old. Been in use for 20 days. There is no icing and I’ve been watching for that. Yes we do get growth but that that much.

Flow, I have this on an adjustable manifold and I measure flow rate at the outside of the boat where it come out. Bucket and stopwatch work well. Each unit has it's own thru haul output so I can measure flow rate and the output water temperature of each unit. The output water temp on this unit run 2-3 degrees less than one running 4.5 gallons when I match the flow rate.

The exact same unit(model number) 18 months old runs well on 4.5 gallons a min.

The Brockerts

 

[tiltrider1]

I would swap with one of your known good units. If the problem follows the unit then it’s a bad unit. If the problem stays with the location then we know it’s a bad installation.

It’s a bit of work but will save you from running in circles.

 

[O C Diver]

What is your dock water temperature? I might consider temporarily connecting it to dock water with an appropriate flow rate. The idea would be to see if a lower temperature makes a difference. Don't know if this is a warranty issue, but being able to determine it functions ok at 80 degrees but not 88 degrees might help arguing that it's not functioning as designed.

BTW, does the owner's manual say anything about maximum temperature for cooling water?

Ted

 

[The Brockerts]

I'll check into my dock water temp in the morning, in the afternoon, after traveling 200 yards to my boat it's hotter than the hot water. I'm not sure I can get 4+ gallons per minute either. Water pressure here in Corpus Christi in the summer is really low.

I've talked to dometic support several times. The input water temp is right on the edge. It's just that I've got other unit's on the same water working just fine.

And here is another thing for the puzzle. This new unit is replacing a 20 year old unit that was doing the same thing in the same location. I replaced the 20 year old unit as it was rusting out everywhere and had to be on it's last days.

The Brockerts

 

[Arc]

Pinch off the other units and go all in with the pump. See if problem goes away. Don’t worry about flow rate for now.

 

[O C Diver]

I'll check into my dock water temp in the morning, in the afternoon, after traveling 200 yards to my boat it's hotter than the hot water. I'm not sure I can get 4+ gallons per minute either. Water pressure here in Corpus Christi in the summer is really low.
⁸7
I've talked to dometic support several times. The input water temp is right on the edge. It's just that I've got other unit's on the same water working just fine.

And here is another thing for the puzzle. This new unit is replacing a 20 year old unit that was doing the same thing in the same location. I replaced the 20 year old unit as it was rusting out everywhere and had to be on it's last days.

The Brockerts

I feel your pain. If you can get there first thing in the morning and try running it off dock water, it may point to a defective or sub standard condenser tube. If you've pushed 10 GPM through the condenser, I'm leaning toward a condenser problem.

Ted

 

[O C Diver]

One more thought.
The higher the fan speed, the more air passes over the evaporator coils, the harder the compressor works, the higher the freon pressure. Try running the blower on the low fan setting and see if it stays running. If it stays on, try the medium fan speed. An air conditioner works hardest when you turn it on and the room is 100 degrees. As the temperature drops, the unit becomes less efficient as the result of a lower fan speed and not being able to extract all the cold from the evaporator freon. Maybe you can use a lower fan speed to get to the less demanding room temperature.

Worth a try.

Ted

 

[The Brockerts]

Ok, the dock water did not work out. It's running 88+ degrees by the time its get to me and the flow rate is a 3 - 3.5 gallons per minutes.

The fan speed work is a good idea and in reviewing the settings it looks like I can change them. I'll start playing with them.

While working in that area I can also adjust the volume of air going into that room. This unit supplies all the cold air for the front berth and some to the kitchen area. It's set at 40(front berth)-60(kitchen). I might try switching this to 60-40. The thermostat is in the front V-berth.

The Brockerts

 

[DrissZougari]

I am just curious about the voltage level at the unit.
on standby mode and when the compressor is on that is.

 

[ksanders]

I would swap with one of your known good units. If the problem follows the unit then it’s a bad unit. If the problem stays with the location then we know it’s a bad installation.

It’s a bit of work but will save you from running in circles.

This is the easiest, fastest way to isolate the problem.

Known good substitution.

yet not one reply

far and away this is the best post in this thread.

 

[The Brockerts]

This is the easiest, fastest way to isolate the problem.

Known good substitution.

yet not one reply

far and away this is the best post in this thread.

I've already started a task and cost list for this swap, and located a helper. I've estimated the cost around $300-500 for labor moving these units, 6 hours of work.

The Brockert’s

 

[Greg QS]

You Have a water flow problem. I have the same set up. 1 pump 4 units. I recently had to clean the lines out. Since its one pump , when the lines start to clog, it diverts the flow to the others until the lines fully clog. Mine runs so much I had barnacles in the strainer, sponges, and other growth . In the lines too. My salon unit is the highest off the water in the system. Always acts up first.

How to fix.
Mine was clogged with marine growth and sediments due to it running almost all the time.
I recently back flushed all the units and lines.
Ran a long zip tie ,3', through the units coils front and back and flushed.
Added valves to each unit lines at the manifold so I could balance the system. This also allows to close all other area and push max flow through 1 line to flush. (really handy for winterizing too!)
I finished out with filling the strainer ( weekly ) with bromine chips to keep the growth at bay.
There was growth and sediment everywhere. I had to change 1 line because I could not clear. This was on the salon unit. The highest in the system.

I used to have to balance the system with the valves at the manifold. Now all are open and I have better flow than I ever have. I have only owned the boat for a 1.5 years. So I got a boat with clogged cooling. LOL

Greg

 

[Turtle Blues]

If you have sufficient cooling water flow and can get reasonable heat transfer on the coil. Suggest measure in and out temps with IR heat gun to confirm.
Then, second check is sufficient air flow. Boxing intake wont help, if there is enough free air grill space unit will draw sufficient air. Have seen the exact scenario you have in picture. Grill was not sufficient to draw a good return air path and unit (both old and new) went off on HP frequently. Does unit operate properly sitting outside the enclosure?
3rd check is the HP cutout switch they can be faulty or too low a psi. They do come in different pressures but this is the last item on the fault list.
Given this is the 2nd unit with same issue My first focus would be on air flow.

 

[The Brockerts]

I'll test a little more before calling this problems solved as I've been running clean for 40 hours.

1 - Changed the De-icing cycle value from 7 degrees to 5 degrees. Somewhere in the installation and setup this got changed to 7 Degrees. Per Dometic Support the setting of 2(7 degrees) for Parameter P-8 is a very rare thing.

I had adjusted the built-in sensor to read the correct ambient room air temp during initial install(P-5) and the thermostat is very close to the in take. I might be able to turn P-8 off all together.

2 - Increased air flow. Current intake is 143 sq inches, with about 30 sq inches blocked a little by the bed over hang I have fixed the over hang to get the full benifit of 143 Sq. inches. Dometic support recommend something more like 160 sq. inches.

Thanks for all the ideas and I'll post once more after I call this problem solved.

The Brockerts

 

[Turtle Blues]

Anything you can do to increase the intake airflow will add to efficiency and total cooling capacity.
I see many new installations where the only consideration was fitting the grill the finished space, not supplying the unit with what it needs.
Any chance of adding a second grill?

 

[The Brockerts]

This problem has been solved:

1 - Changed the De-icing cycle value from 7 degrees to 5 degrees.

2 - Increased air flow to 180 sq inches.

3 - Reduced water flow to 5 gallons per min from 8 gallons per min as recommended by Dometic.

This was a weird combination of settings, air and water flow to produce this problem.

Thanks to everyone watching and responding to this thread

The Brockerts

 

[jimL]

where do you purchase bromine chips?

 

[Don L]

This problem has been solved:

1 - Changed the De-icing cycle value from 7 degrees to 5 degrees.

2 - Increased air flow to 180 sq inches.

3 - Reduced water flow to 5 gallons per min from 8 gallons per min as recommended by Dometic.

This was a weird combination of settings, air and water flow to produce this problem.

Thanks to everyone watching and responding to this thread

The Brockerts

I wonder which of those really solved the problem

 

[PhilPB]

where do you purchase bromine chips?

Pool supply stores, Amazon

 

[fryedaze]

where do you purchase bromine chips?

ACE hardware, Lowes, Home Depot