Hello,

I have a fault with my caravan heating system. The blow heating only works intermittently. Having researched online, I've found that a common issue with my system is the relays on the PCB fail.

I've removed the PCB and tested the five relays (I don't know which controls the blow heating) by putting 9v to them, and they all click; however, one of them gives me this reading when my multimeter is in continuity mode, and the relay should be open. The others all return a 1 on the multimeter. Does the high multimeter reading indicate a fault with the relay?

Thanks for your help

Matt

 

1 means open circuit, 0 will be closed circuit, the relay looks like it has 6 pins , so it might be just normally open contacts?
Can you trace back the heating blow terminals back to the relay then you will know which one it is.

 

I have also found those PCT relays typically have very light circuit traces for the load they handle, also the problem with sealed relays, the interior can become ionized due to contact arcing, leading to contact failure.
Many have a small 'pip' on the top of the relay to open the interior to the atmosphere after manuf.
These relays are sealed due to flux cleaning at construction time.
It may be worth trying a small hole drilled on the relay top for example.
Like this vent hole shown here.

 

1 means open circuit, 0 will be closed circuit, the relay looks like it has 6 pins , so it might be just normally open contacts?
Can you trace back the heating blow terminals back to the relay then you will know which one it is.

Yes, they have 6 pins (I've uploaded the schematic). This is the only one of the five which is behaving this way. The others read that the circuit is open until you energise the relay and the circuit closes. Unfortunately, I don't think I'm technical enough to trace the heating blow terminals back.

 

Yes, they have 6 pins (I've uploaded the schematic). This is the only one of the five which is behaving this way. The others read that the circuit is open until you energise the relay and the circuit closes. Unfortunately, I don't think I'm technical enough to trace the heating blow terminals back.

Okay so it might be stuck closed or it's a normally closed relay, when you power the relay do the contacts open?

 

Okay so it might be stuck closed or it's a normally closed relay, when you power the relay do the contacts open?

I can hear the contact clicking, yes

 

I can hear the contact clicking, yes

And does it read open circuit when it's powered up?

 

And does it read open circuit when it's powered up?

When powered up, it reads that the circuit is closed (which you would expect). The strange reading you get when there's no power to it interests me, as this is only the relay on the board that does that. I've attached two more pictures. The first shows testing the bottom poles of the relay, and without power, the circuit is open (as expected). The following picture shows the top poles of the relay, which shows the reading you get on the multimeter when it's in continuity mode whilst the circuit is still open.

 

If you are reading across two open contacts then you will have the resistance reading due to the load switched by these contacts.

 

If you are reading across two open contacts then you will have the resistance reading due to the load switched by these contacts.

Thanks. So why don't I get that on all the other relays?

 

It all depends on what it is switching? !