Cruisair PR8X Pump Relay Fuse Blowing When 2 Units Operating

[Nick in Manitou]

I will be picking up a clamp-on ammeter somewhere so that I can follow the advice I have been given. I certainly makes sense that the pump may be drawing too much current when it kicks on.

Yesterday I tried to check the strainer for the seawater pump and found I couldn't get it open. I could easily see thorough it and it looks pretty clear, so I would guess that that is not the problem.

I looked at the pump with an eye toward what it would take to check the capacitors and although not convenient to access, I assume it could be done.

While looking over the whole system, I found a label in the PR8X pump relay box that stated that the 10 amp fuse that the box was supplied with could be replaced with a higher amperage fuse (not to exceed 20 amps) if the pump required it and if the wiring was sized correctly. Since the wiring used in this case is 10ga, I went ahead and replaced the 10 amp circuit breaker with a 20 amp unit. (Again, this is the circuit breaker I installed in the pump relay box replacing the fuse that had been there. The pump itself is on a 15 amp breaker in the panel in the engine room. Also, this circuit breaker is at a point in the circuitry where the manufacturer decided it was extraneous and had removed it from later examples of the pump relay.)

Overnight and so far this morning, the system has functioned without an issue.

I do intend to pursue determining the amperage draw even if there is no further issue with the circuit breaker popping.

Nick

 

[rustybucket]

I will be picking up a clamp-on ammeter somewhere so that I can follow the advice I have been given. I certainly makes sense that the pump may be drawing too much current when it kicks on.

Yesterday I tried to check the strainer for the seawater pump and found I couldn't get it open. I could easily see thorough it and it looks pretty clear, so I would guess that that is not the problem.

I looked at the pump with an eye toward what it would take to check the capacitors and although not convenient to access, I assume it could be done.

While looking over the whole system, I found a label in the PR8X pump relay box that stated that the 10 amp fuse that the box was supplied with could be replaced with a higher amperage fuse (not to exceed 20 amps) if the pump required it and if the wiring was sized correctly. Since the wiring used in this case is 10ga, I went ahead and replaced the 10 amp circuit breaker with a 20 amp unit. (Again, this is the circuit breaker I installed in the pump relay box replacing the fuse that had been there. The pump itself is on a 15 amp breaker in the panel in the engine room. Also, this circuit breaker is at a point in the circuitry where the manufacturer decided it was extraneous and had removed it from later examples of the pump relay.)

Overnight and so far this morning, the system has functioned without an issue.

I do intend to pursue determining the amperage draw even if there is no further issue with the circuit breaker popping.

Nick

Good to hear! A clamp on amp meter is pretty much required equipment when working on these older boats. It takes a LOT of the guess work out of tracking electrical issues. The one I keep on the boat came from home depot and was only like $75. This is not an item I'd suggest getting at Harbor Freight. You need a little better than HF but not as good as an expensive fluke. Something in the $75-$100 range should work well for you.

 

[Nick in Manitou]

Rustybucket,

Thanks for the suggestions about quality of clamp-on ammeter to go with. I was actually intending to ask what level of quality ($$) was required. Saving a buck and ending up with something less than can be depended on is certainly a poor choice, but spending more than I need to is something I try to avoid!

Thanks,
Nick

 

[Photolomy]

I noticed that the new relays come with a 15 amp fuse, not a 10 amp fuse.

 

[Boatsb]

I have a bunch of meters. Newer, lighter and fancier than the one I use almost all the time. The 20 year old fluke.

It's worth the investment m

 

[Reefgeorge]

Fluke makes good stuff but expensive.

I use mostly Extech, less expensive but not cheap.

I see that Amazon has an amp probe for less than $30 which gets good ratings but I can't vouch for the quality

George

 

[Nick in Manitou]

Thanks for the suggestions on the meters!

Nick

 

[Nick in Manitou]

Just wanted to update this thread.

4 days ago I replaced the 10 amp push button circuit breaker that I had installed in the PR8X pump relay box with one rated at 20 amps. (The schematic in the PR8X box indicated that 20 amp protection was acceptable.)

I have been running the units on heat for the last 4 days, sometimes 2 units at once and have not had the circuit breaker trip even one time.

The support tech at Dometic had said that the problem with probably in the fuse holder itself as the spring gets weak and causes too much resistance. I believe that in this case he was correct. I was blowing 20 amp fuses one after the other and now, with the 20 amp circuit breaker in place of the fuse holder I am having no trouble. (Hoping that continues!)

Now I need to find a source for a serviceable Honeywell thermostat for these units. They are line voltage units and not easy to find.

Thanks for all the help!
Nick

 

[rustybucket]

Just wanted to update this thread.

4 days ago I replaced the 10 amp push button circuit breaker that I had installed in the PR8X pump relay box with one rated at 20 amps. (The schematic in the PR8X box indicated that 20 amp protection was acceptable.)

I have been running the units on heat for the last 4 days, sometimes 2 units at once and have not had the circuit breaker trip even one time.

The support tech at Dometic had said that the problem with probably in the fuse holder itself as the spring gets weak and causes too much resistance. I believe that in this case he was correct. I was blowing 20 amp fuses one after the other and now, with the 20 amp circuit breaker in place of the fuse holder I am having no trouble. (Hoping that continues!)

Now I need to find a source for a serviceable Honeywell thermostat for these units. They are line voltage units and not easy to find.

Thanks for all the help!
Nick

Good to here, but you really should still measure the amp draw of the motor.

 

[Nick in Manitou]

I do intend to pick up a clamp-on ammeter and check to make sure that everything is as it should be. (We are still trying to settle in onboard and the priority list of things that need to be none ASAP is pretty long!)

Since it seems that the fuse holder itself may have been at least part of the problem, I wanted to get that statement out there so that others who may run into a problem with blowing fuses in the pump relay box would know to check out that possibility.

I do agree it would be wise to check the current draw when the pump comes on...and I will do it!

Thanks for the reminder, RustyBucket!

Nick