SCS Basement Unit Repair and Mods

SCS Basement Unit Repair and Mods - Printable Version

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+--- Thread: SCS Basement Unit Repair and Mods (/showthread.php?tid=7503)

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RE: SCS Basement Unit Repair and Mods - [email protected] - 07-28-2025

(07-28-2025, 01:30 PM)Richard Wrote: Keep this in mind when wiring a modified control board to the existing tstat. The outdoor fan speed is controlled by whether one or two compressors are called for. The tstat controls the indoor fan speed . So in wiring the mod board you must make provisions that the lo signal to the out door fan is interrupted when the second compressor comes on.

I accomplished this with a relay for the outdoor fan connected to the same control wire as the compressor 2 signal from the tstat. The 120v for the fan comes from the compressor 1 120v source through a normally closed contact, so that when compressor 1 comes on it also starts the fan on low speed, when the 2nd compressor kicks it changes the fan relay to change to high speed.

See the yellow highlights on my drawing:

RE: SCS Basement Unit Repair and Mods - AlanJohnson - 08-04-2025

I'm having trouble figuring out how the aquahot ties into this. I know in the past if I turned on electric aquahot the ac immediately went to low speed. Here is what I see from the thermostat control wires.

Cool Fan Aquahot Wires that are hot at this setting
-------- --------- ------------ ---------------------------------------
Low Low off yellow red
High High off yellow orange black
Low Low ON no change, but not relevant either
High High ON yellow orange black (no change)

Based on this things, I use yellow as compressor 1 (or low/low). Orange as compressor 2, high/high. (yellow is still hot).
I only have 1 evap fan setting, high.
I have 2 condensor fan settings, high/low, depending on if both compressors are on.

I don't know what I would use red or black hot wires for... but maybe this is where i am missing something.

Thank you,
Alan

RE: SCS Basement Unit Repair and Mods - [email protected] - 08-04-2025

(08-04-2025, 08:20 AM)AlanJohnson Wrote: I'm having trouble figuring out how the aquahot ties into this. I know in the past if I turned on electric aquahot the ac immediately went to low speed. Here is what I see from the thermostat control wires.

Cool Fan Aquahot Wires that are hot at this setting
-------- --------- ------------ ---------------------------------------
Low Low off yellow red
High High off yellow orange black
Low Low ON no change, but not relevant either
High High ON yellow orange black (no change)

Based on this things, I use yellow as compressor 1 (or low/low). Orange as compressor 2, high/high. (yellow is still hot).
I only have 1 evap fan setting, high.
I have 2 condensor fan settings, high/low, depending on if both compressors are on.

I don't know what I would use red or black hot wires for... but maybe this is where i am missing something.

Thank you,
Alan

Maybe this will help Alan:
https://youtu.be/IWQsaAqF_tg?si=PvNbNBMPbZCz7DZe

For reference:

RE: SCS Basement Unit Repair and Mods - AlanJohnson - 08-06-2025

When you say the striped wire is for heat and "goes to the aquahot". I assume you mean it turns on a circulating pump for the aquahot, yes?

Is your bedroom AC limited to 1 compressor if you turn on electric for hot water (as opposed to diesel)? Mine is. So if I have 2 compressors running, and flip the Electric Aquahot switch, one of my compressors turns off, and the condensor fan switches to low. BUT I don't know how it does this. I could not make any thermostat wires switch on/off when I flipped the water heater on/off.

Sorry if I'm being dense about this. lol

RE: SCS Basement Unit Repair and Mods - [email protected] - 08-07-2025

(08-06-2025, 05:48 PM)AlanJohnson Wrote: When you say the striped wire is for heat and "goes to the aquahot". I assume you mean it turns on a circulating pump for the aquahot, yes?

Is your bedroom AC limited to 1 compressor if you turn on electric for hot water (as opposed to diesel)? Mine is. So if I have 2 compressors running, and flip the Electric Aquahot switch, one of my compressors turns off, and the condensor fan switches to low. BUT I don't know how it does this. I could not make any thermostat wires switch on/off when I flipped the water heater on/off.

Sorry if I'm being dense about this. lol

So the aqua hot wire goes to relays on the aqua hot, the relay does all the work of turning on circulating pumps for that zone. The aqua hot temp is controlled by the thermostat in the aqua hot for either electric or diesel.

My electric aqua hot switch shuts off the front air completely. I suspect they are doing the same thing as mine except they are just turning off one of the two circuits that supply the air conditioner. You should have 2 AC breakers for each unit, one for each compressor. I beleive mine has a contactor near the electric panel and that contactor shuts off the AC when you turn on the electric to the aqua hot, has nothing to do with the thermostat wiring, it’s all done with the power wiring.

RE: SCS Basement Unit Repair and Mods - Richard - 08-07-2025

I am the most dense, in that I do not understand what Tstat Alan is using. I do not understand what he means by fan goes to low. AC fan? Aquahot kick heater fan?

As shown in Jeff’s pic, if a Tstat has the heat function, it is usually the white wire or terminal. It will connect to yellow with red stripe wire. This turns one the fans for the kick heaters. It does not turn on the Aquahot as others have stated.

The aquahot/AC switch at the microwave panel has caused all kinds of confusion over the years. If flipped to AC the electric heaters in the AH will not activate. If flipped to Aquahot, the ACs will not energize. This is a separate switch from the Aquahot Diesel activation switch.

Why repeat all that? Over the years some owners rewired that energy management switch so that they could get electric AH heat AND AC use. I realize I am making the same points that Jeff and Gordon made.

Look for a grey rectangular box below the 120 panel in the rear closet. Have someone flip the AC/Aquahot switch while you are standing close to the box, and you should hear it click.

RE: SCS Basement Unit Repair and Mods - AlanJohnson - 08-07-2025

"My electric aqua hot switch shuts off the front air completely. I suspect they are doing the same thing as mine except they are just turning off one of the two circuits that supply the air conditioner. You should have 2 AC breakers for each unit, one for each compressor. I beleive mine has a contactor near the electric panel and that contactor shuts off the AC when you turn on the electric to the aqua hot, has nothing to do with the thermostat wiring, it’s all done with the power wiring."

Jeff, Ok, I understand now. I kept thinking this was done at through wiring at the thermostat. I did not know there was another contactor somewhere.

Thanks,
Alan