Caravan pump circuit

[ianb]

Hi, would be really grateful for any advice. Having a problem with our water pump fuse blowing on Coachman 525. We had an issue with the pressure switch on our last trip, so used the control panel pump on/off to control the truma sub-pump. When I replaced the pressure switch with the new version, (checked wiring and instructions) turned on but didn't work. Checked fuses, and the 10amp pump fuse had melted. When I replaced the fuse and turn on the pump at the control panel, fuse blows. So, I've replaced the control panel, didn't work, replaced the PCB in the consumer unit, didn't work, fuse still blows when connected. Looks to be an issue with the negative return wire to the fuse box. But, before I go stripping cables to check for a short circuit, any thoughts or advice would be really appreciated. Everything else including toilet flush (which uses the pump fuse) works fine ??? Thanks, Ian

 

[ProfJohnL]

From the sequence of events you have describe, it suggests the failure of the fuses is related to the installation of the new pressure switch. You must have removed and remade some connections, and I am of the opinion you must have made a mistake with your rewiring. If you are unfamiliar with caravan wiring I suggest engaging a professional.

 

[JTQ]

How many connections does the new pressure switch have?
Years since I had one, [thankfully.]

 

[Beardy]

Hi, would be really grateful for any advice. Having a problem with our water pump fuse blowing on Coachman 525. We had an issue with the pressure switch on our last trip, so used the control panel pump on/off to control the truma sub-pump. When I replaced the pressure switch with the new version, (checked wiring and instructions) turned on but didn't work. Checked fuses, and the 10amp pump fuse had melted. When I replaced the fuse and turn on the pump at the control panel, fuse blows. So, I've replaced the control panel, didn't work, replaced the PCB in the consumer unit, didn't work, fuse still blows when connected. Looks to be an issue with the negative return wire to the fuse box. But, before I go stripping cables to check for a short circuit, any thoughts or advice would be really appreciated. Everything else including toilet flush (which uses the pump fuse) works fine ??? Thanks, Ian

From your description the two most likely culprits are the pressure switch or the pump. It's possible that the pump was damaged when you ran it without the pressure switch (though unlikely it's possible to fail in a way that causes the fuse to blow). I'm assuming that you have an external water pump and aquaroll - does the fuse blow if you unplug the pump then switch the pump on at the control panel? If the fuse doesn't blow it points towards a pump fault, if it does it points towards the pressure switch.
Could you try refitting the old pressure switch and running the pump? This would prove that the pump is OK and point towards the pressure switch.

 

[ianb]

Hi, thanks for the replies. Wiring ok as the instructions, I reconnected the original switch to check whether it was the new one, but still blew fuse. Pump is not connected at the moment. So, must be something in the circuit. I'm fairly competent with electrics and DIY, but this is baffling me ? The new pressure switch has two -ve connections, the original had three connections. Instructions state only connect the -ve to the new pressure switch. Thanks

 

[ProfJohnL]

They symptom suggests the pressure switch is shorting out the pump supply, which is blowing the fuse. You have now told us that the new switch has only two terminals, and you have connected the negative to the switch. This has to be wrong, becasue that will make the switch short out the supply, which is exactly the symptom you have reported.

The 12V positive supply needs to go to one of the terminals on the switch, and the pumps 12ve cable needs to go to the other terminal on the switch.

You then need to connect the -ve supply wire to the pumps negative wire.

I'm pretty sure you have mixed up the wiring.

 

[birdman101]

A standard pressure switch only has 2 connections one positive feed and the other connection wire goes to the pump positive. There should be no negative connected at the pressure switch. The negative on the pump should be direct to the consumer unit negative.

 

[Beardy]

A standard pressure switch only has 2 connections one positive feed and the other connection wire goes to the pump positive. There should be no negative connected at the pressure switch. The negative on the pump should be direct to the consumer unit negative.

I'm guessing that he had something like this and is replacing it with a standard switch. Without a circuit diagram I can only surmise that the pump would have a permanent 12v supply and the 'smart switch' switches 0v. To replace it with a standard switch you would connect the 'pump -' and 'batt -' to the terminals on the new switch.

ianb, It might be useful if you could post photos of the old and new switches.

 

[JTQ]

We are being told that replacing it with the removed switch also resulted in blowing the fuse; so its not the new switch that's causing the problem.
Candidates could therefore include, how its wired and the wiring itself on the "return" .

Is the system one where the switch feeds power to the pump or grounds the pump enabling it to run?