[Richard]

Way to hang in there. I am glad Miss Hannah is now warm.

Seriously, understanding how relays work is a critical skill in maintaining your Newell. I am going to post info from a basic google search and then add the Richard explanation.

Pinout Function Breakdown
85 (Coil Ground): Connects to the ground/chassis.
86 (Coil Input): Connects to the +12V trigger switch (e.g., ignition or toggle switch).
30 (Common Input): Connects to a fused +12V battery power source.
87 (Normally Open Output): Connects to the positive lead of the accessory (e.g., lights, fans).
87a (Normally Closed Output): Connects to devices that should be on until the switch is flipped (5-pin only).

Let’s think of the relay as a remote switch. If you supply 12V positive to terminal 86 and ground to terminal 87, the switch closes. The switch that closes connects terminals 30 and 87. Terminals 86 and 87 require almost no amperage so you can run a skinny wire from the cockpit all the way to the relay in the rear of the coach. Terminals 30 and 87 are rated to carry 20 or 30 amps. This requires 10 gauge heavy wiring. This allows you to wire the heavy amperage device through the relay (30 and 87) and turn it off or on with a light duty switch and wiring many many feet away. The alternative is to run the heavy wiring the length of the coach and use a heavy duty switch.

This concept is used FREQUENTLY with electrical motors on the coach. For example the control boards supply minuscule current to a relay which powers the AC compressor. The transistors on the control board cannot handle the amperage that the AC compressor draws.

Now in the case of the AH, this is not the common use of the relay but the principles are the same. The trigger is the 12V output from the Tstat. So the tstat output goes to term 85, and term 86 is wired to ground. When the tstat sends the signal then the relay activates and terminals 30 and 87 are now connected or closed. Instead of running power through them as normal, terminal 87 is wired to ground, and terminal 30 is wired to the input the AH relay is looking for to start the heat. Sorry I don’t remember that terminal off the top of my head. When the relay is activated by the 12V pos signal to terminal 85, the contacts close between 30 and 87 which connects the AH signal to ground.

Most decent relays will have the picture printed on the back showing which terminals do what. When looking at the picture , the thing that looks like a coil of wire is the trigger circuit. Think about it is the old wire wrapped around a nail, hooking the wire to a battery and turning the nail into a magnet. That is exactly what happens in the relay. The coil of wired inside is connected to voltage and turns into a magnet. The magnet closes the switch contacts.

One final thing, to be aware of. The cube relays discussed above are 4 prong relays. You can buy 5 prong relays in two different configurations. The first will have the fifth terminal as NC normally closed which means it will disconnect when the relay is triggered. The second has two NO terminals for power and both will be closed when the relay is triggered and send power to both terminals.

[Pluto]

Thanks for the detailed information, Richard. Once I realized what the thermostat was doing I installed two new relays at the aquahot, one for the living room and one for the bedroom. I  also installed a new thermostat in the bedroom today and we now have functioning heat and ac on that thermostat.