[Chester Stone]

Richard, I have received the parts and have reviewed your posting and schematics, but I would appreciate a little more information. In your schematic, you show dotted or dash colored wiring going from the board to the relays. What type of size of wiring is this? There are four posts on each relay designated L1, T1, A1 and A2. This may be a dumb question, but which wires go to which post?

[Richard]

Lets cover in concept what this modification does. The mod takes the high current of the compressors of of the circuit boards and runs the compressor current through external relays. The two small terminals(A1 and A2) on either side of the contactor are the terminals for the contactor coil. When they see 120VAC the coil will energize and pull the contacts together. The trigger for the contactor is the voltage that normally would go to the compressor. By cutting the two wires from the board to the compressor, the wires are extended and used to trigger the contactor.

The two large terminals (L1 and T1) are designed to carry heavy wire and heavy current. One side, usually L1 will be wired to one of the hot legs of the coach AC system. The other side, T2 will be extended to connect to one of the two wires going to the compressor.

The second wire going to the compressor will be wired to neutral. It doesn't matter which since this is an AC circuit.

This is how to execute the concept.

Ok, A1 and A2 are the trigger for the relay coil. Run the two wires FROM the compressor output on the board to those terminals. You can use small wire since the current is about 0.3 amps. The two big terminals are L1 and T1. On one side of that you will wire either black or red hot 110. On the other side run the output to one of the two wires going to the compressor.

Remember, looking at the diagram that you also have to run neutral (white) to the other compressor wire to complete the circuit. Neutral does not go through the relay.

When you wire the second compressor, use the hot source that you didn't use on the first relay. That keeps the two compressors on separate legs to balance the load.

The board still requires all of it's 120VAC connections to power the circuitry and the fans.

The second thing to remember is that when you do the second unit. If you used black to power the first compressor on unit 1, then use red to power the first compressor on unit two.

[Chester Stone]

Richard, I have attached a schematic (now in color) which was included in one of your prior posts on this relay subject.  In this schematic, the common goes through both relays.  I suspect this is not necessary.  Also, as to compressor 2, the large blue wire turns to purple and the red turns to yellow.  Is this because these are the colors that exist going to the second compressor?  I would appreciate your review of the colored schematic and comment.  Thanks bunches.
   

[Richard]

On Mark's diagram, he chose to use a two pole contactor and he interrupts both the hot and the neutral leg. If you look at my schematic in the original post, I only interrupt the hot leg but I run a separate neutral to the compressors to take the load off the board. Both methods work and accomplish virtually the same thing.

I don't comment on wire colors because they could be different from coach to coach. That's why I stick to trying to explain the fundamentals and have the installer apply the fundamentals to their unique situation. I am not trying to be a smart aleck. When Bill and I did the install on his coach we discovered his wiring was not exactly like mine.

[77newell]

From the diaphragm shown earlier in this thread it seems that the thermostat logic decides the number of compressors running and the CB provides ptotection against short cycling and maybe determining the fans that are running at any given time.

Under this configuration, if the circuit boards become unavailable but the system is otherwise functioning fine then it should be possible to substitute a small programmable logic control (PLC) for the circuit board. It wouldn't be as cheap as the board but would allow continued use of the system.

[Chester Stone]

Richard, you are correct since I purchased single poll relays.  Please look over the attached to see if I have done it correctly.
   

[bikestuff]

Chester,

That looks right.  One slight change that we did on mine was to tie all the neutrals on each compressor(White wires) together.  Made the connections a little easier.  This means that only a single hot wire is connected to each compressor connector on the board.

Remember that you will need to be careful with the little connectors that go on the board.  I think that you may need to splice wires onto the old pig tails to reach your new relays.

The little purple connectors are from Lowes and make the neutral connections easier / more secure.

Here are some pics of my installation.

bill

[Chester Stone]

Bill, thanks for posting the photos. After studying them, I think my schematic is entirely wrong. Looks like the primary heavy wire feed through the relays is simple enough, but the smaller wires (pigtails) are not correct. Did you by chance draw out a schematic of how you wired the relays to the pigtails? I will study your photos more tomorrow to try to correct by schematic.

[Richard]

Chester,

You got it !!!!!

Wire it like you drew it.

Remember to reverse red and black on the second AC unit contactors. That way, you keep the power balanced on the legs as much as possible.

Don't let Bill's pictures fool you.

You could also take the neutral that will be in your junction box and connect that to one side of the triggers. You save running two wires that way. But's it's more fool proof for you to wire it the way you drew it.