Cruisair PR8X Pump Relay Fuse Blowing When 2 Units Operating

[Nick in Manitou]

New to Boating. New to Forum.

1984 53' Extended Deckhouse

Using 2 Cruisair systems onboard for heat. They seem to work fine individually. Both operate the same seawater pump when their compressors are running. Everything seems to be fine unless we try to operate them at the same time. If we do, after a while we realize we are getting cold and that the seawater pump is no longer working...the 20 amp fuse in the PR8X has blown.

I have put my hand on the pump after it has been running for hours and it is just warm - not at all hot.

I don't have a lot of experience with AC systems, but it seems that if a pump is running and another unit calls for that same pump to turn on, that there would not be a significant change in the power being consumed by the pump circuit.

What might be the cause of the fuse blowing? It has happened 3 times so far, but if we run only one unit at a time, we are going on more than two days now without a blown fuse.

Any thoughts? Any experience with this problem?

Thanks for any help!

Nick

 

[Boatsb]

Voltage drop from a second unit running.

As the voltage drops the pump gets browned out and blows a fuse.

 

[SEVEN]

Welcome to the forum. I’ll take a guess because I’m not there in person. The fuses are old and weak. Try switching them out. If that’s it, it’s a cheap fix. Question, what power do you have going to the boat? 50/125/250?

 

[Photolomy]

Where is this fuse? The water pump has a breaker, no? Also, the controller only turns on the water pump once, that I am aware of, no matter how many AC units are turned on. I wasn't aware that it speeded it up as more units are turned on. As far as I can see, the pump feeds a manifold that then distributes the water to all of the units equally, regardless of whether they are running or not.

 

[Nick in Manitou]

We have 240V to the boat.

The fuse is a 20amp SFE (slow-blow?) fuse that looks like the old automotive size/style fuses. Box was onboard when we arrived 2 weeks ago and appears to be new.

The fuse holder cap sticks out of the top of the PR8X box.

I assume that the pump would operate at a fixed speed no matter whether one or more units call for it to be operating. The pump feeds water to a manifold that supplies water to all the Cruisair units.

I must admit that I assume that there is a breaker for the pump, but I have not specifically looked for one (yet).

Nick
(in San Francisco...it is cold enough to want the heat to work!)

 

[Photolomy]

I see. I haven't had to look at mine, but the PR8X is a set of relays that turn on the water pump if any AC unit is on, but the fuse in it supports the relays, not the pump. The pump is supported by a breaker in the helm. My guess is that the fault is in the PR8X, not the pump. Maybe one of the relays is bad, or the controller circuitry is bad and burning out the fuse. You could test which by turning on the other two AC units and seeing if that also burns out the fuse. But I don't think the water pump has anything to do with this issue.

https://citimarinestore.com/en/parts-displays-accessories/7230-cruisair-pr8x-pump-relay-115-230v.html#/1776-control_triggers_included-four_115v_triggers_115

I have the same box and might take a peek inside this weekend.

 

[Nick in Manitou]

I just spoke with a fellow at Dometic in product support for Cruisair.

He said that the problem is probably the fuse holder itself. He said that the spring in the fuse holder is weakened by heat over time and ends up not holding the fuse with enough pressure to maintain a good connection, building up heat and causing the fuse to blow. He said that they eventually eliminated the fuse from the design as the pump is protected by a breaker.

Perhaps this makes sense, as I was getting a brain cramp trying to figure out how we were blowing a 20 amp fuse in a circuit that is supposedly protected by a 15 amp breaker.

He suggested I just bypass the fuse holder and depend on the breaker to protect the circuit. I must admit that this makes me a little nervous. (I hate removing protection from a circuit where the wires are bundled up together with lots of other wires for other circuits...!)

Nick

 

[Cricket]

Wouldn't eliminate the protection of the fuse. Just replace the fuse holder or do what we did, changed the fuse holder to a breaker, fit in the same hole.

 

[Nick in Manitou]

Cricket,

What was the source for your fuse-holder-replacement circuit breaker?

I do like that idea much better than just hard-wiring the fuse out of the system.

The fellow I spoke with at Dometic said that the fuse was originally a 10 amp fuse. What size breaker are you using?

Thanks!
Nick

 

[Cricket]

The boat is laid up for the winter and not close.
Not sure what size breaker, most likely whatever size fuse it originally came with.

Pretty sure it's like these.
https://www.bluesea.com/products/21...Only_Screw_Terminal_Circuit_Breaker_-_15_Amps

 

[Nick in Manitou]

Well Shucks.

I liked Cricket's suggestion of replacing the fuse holder with a fuse. Since the tech support guy at Dometic said that the unit originally came with a 10 amp fuse, I went to West Marine and picked up a push button 10 amp breaker and installed it expecting my troubles to be over.

I started up the unit that supplies heat/cooling to the galley and v-berth and the circuit breaker popped very quickly. (I could hear the pump turning over very slowly - really laboring. I had not heard the pump doing that before...but maybe I was not where I could hear it when it did...) I tried resetting the circuit breaker a couple of times and had the same result.

I then turned off the v-berth system and tried the unit that supplies the master stateroom. It worked and the pump sounded fine (although I was not where I could hear it clearly during the first couple seconds of its operation, through the walls it sounded as though it came up to speed immediately).

I called Dometic again and eventually get a call back and had a long discussion about what might be the problem. During the telephone call the system continued to run without an issue operating the master stateroom unit.

After the call, since the system was running fine, I decided to try adding the v-berth unit...and it is working.

So, where we are at the moment is not very clear:
>Is the problem with the pump, in that perhaps it occasionally has trouble starting due to an internal problem with the motor?
>Is the problem with the trigger activated by the v-berth unit controls in that it (sometimes) sends only partial voltage to the pump?
>Is there a problem with the P.C. board in the PR8X relay box that is causing the pump to (sometimes) not start properly?

Right now, the boat is warming up (and there is a heck of a storm outside) so I am going to leave well enough alone. I will dig back into it tomorrow.

(My guess at the moment is that the trigger associated with the v-berth unit is bad. There are a couple currently unused triggers in the PR8X and if they are the correct voltage, I will try swapping one of them for the one currently associated with the v-berth unit.)

Again, any input is appreciated!

Exciting times for a couple folks new to boating to be bouncing around in a rather major storm!

Sorry for the long-winded post, but I figured that if I gave all the details I could, the solution might be obvious to one of you.

(I should point out that I am VERY impressed with the support from Dometic!)

Nick

 

[Briankinley2004]

Nick have you tried turning the V berth on first then the master to see if V berth runs fine without the master? Then when the master kicks on does the issue replicate? If so I would suspect something with the pump or a voltage issue. If you think it is in the PC board or trigger are they the same type on each unit? If so try swapping them and see if the issue reverses itself. If so its probably the suspect parts you swapped. If not its something else

 

[Nick in Manitou]

Brian,

When I first tried the system after installing the circuit breaker I started the galley/v-berth system first and saw the issue with the pump turning over very slowly. I eventually gave up and tried the stateroom system and had no trouble. Later I added the galley/v-berth system to the mix with the pump already running (started by the stateroom system earlier).

I have not experimented further this evening because since we have heat, I didn't want to mess with a good thing, plus since we may lose power due to a significant storm in the San Francisco area (many areas are already without power) we figure let's get it warm and keep it warm and experiment tomorrow when things calm down a bit.

I like the idea of swapping the triggers to see if the problem follows the trigger!

Nick

 

[kelpy]

Does the same issue occur when running on the generator?

 

[rustybucket]

I would almost suspect a motor capacitor on the pump. A bad capacitor would satisfy all the symptoms (as I am interpreting them). An amp spike when the motor starts causing the motor to struggle, especially in a voltage drop situation (such as when both units on) but able to overcome it when the systems are staged on. Lower voltage equals higher amps, possibly the voltage drop is just enough to push the amps over the trip level of the fuse/breaker.

You could clamp an amp clamp on a lead to the motor to see what kinda amps it's drawing at start/run. Is pretty easy to check the cap(s) on it as well and a VERY cheap fix if that's the issue.

I'd be tempted to measure amps on the motor at start/run. Then also voltage of the system as the units are turned on (this will take two people). If you see an amp spike on the motor and a voltage drop when everything is powered up then I would pull the capacitor and test it. Or if you have a spare handy just plug it in and give it a test.

A second consideration. Is the pump a higher amp pump than what was originally installed on the system?

 

[Reefgeorge]

As suggested above, you need to look at amp draw and voltage in each section of the system. In particular the compressor(s) and water pumps for excessive current and all points in the power distribution for abnormal voltage drop/resistance. The later is the reason for the fuse holder replacement suggestion but wiring, connections, marginal breakers etc can all be the fault. You don’t have to guess but some systematic analysis is necessary. If you want some help isolating and measuring let me know and I will help you get to the bottom of it. If you prefer to swap parts then I would go with clean all connections, replace fuse holders and breakers one at a time then a water pump rebuilt including capacitors, then condensing unit capacitors both run and start.

Let me know if I can help further.

George

 

[Nick in Manitou]

Thanks for all the responses.

We are still in the fact finding stage. Every time I think I have nailed something down, I find out that I was incorrect!

The master stateroom system ran overnight, working for a while and then the seawater pump quit at some point popping the 10 amp circuit breaker I installed in place of the fuse on the pump relay box.

When we got up this morning I reset the breaker and tried to get the system going without success - first trying the master and then trying the v-berth units.

Turned on the electric heat and had breakfast, then tried both systems individually and they each worked!

I have occasionally looked at display for the voltage to the boat and it has never been below 237 or above 244 that I have noticed. (I don't have any idea of how accurate the meter is...it is built into the large breaker panel by the steps down to the galley.)

As I stated at the beginning of this thread, we are new to boating and have owned and been aboard this boat for just over 2 weeks. Everything is new to me. I am trying to set things up and get things working in between figuring out how to fit into a boat after 35 years of living in houses.

I was told that the strainer for the seawater pump had been checked, so I have not bothered to check it again, but perhaps it is time to start at the basics. I will start with that and while upside down under the exhaust I might as well see what I can learn about the pump motor.

Nick

 

[rustybucket]

Each shorepower is different. I have to be really careful how much I run at the dock. If I do too much I trip the breaker on the pedestal. Dock power is notoriously 'weak' i guess you could say. Low voltage leads to high amps which leads to strain on wiring, motors and breakers.

You need to be measuring the voltage/amps when everything kicks on.

Thanks for all the responses.

We are still in the fact finding stage. Every time I think I have nailed something down, I find out that I was incorrect!

The master stateroom system ran overnight, working for a while and then the seawater pump quit at some point popping the 10 amp circuit breaker I installed in place of the fuse on the pump relay box.

When we got up this morning I reset the breaker and tried to get the system going without success - first trying the master and then trying the v-berth units.

Turned on the electric heat and had breakfast, then tried both systems individually and they each worked!

I have occasionally looked at display for the voltage to the boat and it has never been below 237 or above 244 that I have noticed. (I don't have any idea of how accurate the meter is...it is built into the large breaker panel by the steps down to the galley.)

As I stated at the beginning of this thread, we are new to boating and have owned and been aboard this boat for just over 2 weeks. Everything is new to me. I am trying to set things up and get things working in between figuring out how to fit into a boat after 35 years of living in houses.

I was told that the strainer for the seawater pump had been checked, so I have not bothered to check it again, but perhaps it is time to start at the basics. I will start with that and while upside down under the exhaust I might as well see what I can learn about the pump motor.

Nick

 

[Reefgeorge]

Get a voltmeter and a clamp on ammeter.

Here is an example of a way to approach this. To check the water pump for excessive amp draw either because its failing or there is a voltage drop, set up the clamp right before power to the motor and get a voltage at the same spot. Either watch those during the time that things trip offline or set up a video camera looking at the readouts and go look at it after the system quits. Then you will know if the motor needs repair or replacement. That just one example. You isolate and repeat this in sections to find out where the problem is. You can either start at the loads and work towards the power cord or the converse.

Intermittent electrical problems are fun for you and me,

George

 

[rustybucket]

Get a voltmeter and a clamp on ammeter.

Here is an example of a way to approach this. To check the water pump for excessive amp draw either because its failing or there is a voltage drop, set up the clamp right before power to the motor and get a voltage at the same spot. Either watch those during the time that things trip offline or set up a video camera looking at the readouts and go look at it after the system quits. Then you will know if the motor needs repair or replacement. That just one example. You isolate and repeat this in sections to find out where the problem is. You can either start at the loads and work towards the power cord or the converse.

Intermittent electrical problems are fun for you and me,

George

Excellent advice on using the video camera. I've used facetime and skype (video conference call) several times to monitor something in another room.