[ashley]

Lost both boards due to low ac volts. Both boards failed in the same place, a relay on the board. If you are in a park that has low volts do not run in high, just start the generator, if you need high. Basement Air

[Richard]

Ashley

Sorry to hear that.
A couple of us have implemented heavy duty remote contractors to take the amperage load of the compressors off of the boards. It seems to be working well for me. Let me know if you want details.

[ashley]

Yes Richard let me know.

[Yachts]

But I must say you have a fine looking coach under the tree

[Richard]

All that I am about to explain and recommend is not new or original to me. I do believe that @"RussWhite"  was an early identifier of the inherent weaknesses of the circuit boards in the SCS air conditioners. So I am repeating what I have learned from other gurus and how I went about hopefully solving the issue. I will admit upfront that the solution is like killing a fly with a tank but Rhonda does not tolerate heat due to a heatstroke years ago. AC is very important to her, and therefore me.

The problem is that each of the two compressors in the system pull around 15 amps on a hot day and they run almost continuously. That doesn't include the surge amperage either which adds to the issue each time a compressor starts. The circuit board apparently does not have the robustness to carry that kind of current. There are three known problem areas. The first is the "lands" or the silver lines on the board that conduct the electricity are not heavy enough to withstand the current. The second problem is that the plug where the compressor wires attach to the board is not heavy enough to carry the current. The third is that the relays on the boards that engage to power the compressors do not last forever running that much current.

All of these problems are compounded with low voltage or loose connections in the wiring which raises the amperage even further. Low voltage/ high amperage will cook the board if you are lucky, and cook the compressor if you are not.

Some have been successful in soldering wire on the back of the board to help carry the load, and I think the new ones come from Newell with the wires already added. Some have replaced the compressor plug with a soldered connection. And some send the boards out to have the relays replaced.

All of that to get the the overengineered solution.  This solution is simple in concept, and not too hard to implement if you understand basic AC electricity. The concept is this. Snip the wires that would normally feed hot and neutral to the compressors. Use snipped end on the circuit board side to trigger an external heavy duty motor contactor. Power the compressor from the contactor by connecting the snipped ends on the compressor side to the contactor. So instead of the circuit board turning on the compressor and pulling 15 amps through the board for each compressor, the board merely turns on the contactors. The contactors pull about 0.25 amps. The load on the board is now reduced significantly. The board will still power the fans which pull around 2 amps each, but this solution takes around 14 amps off each side of the board.

I used 30 amp definite purpose contactors and mounted them in a remote box outside the unit on the wall above. The contactors were about $25 each from McMaster, the boxes another 20 each, and wire and connectors probably another 30. The total cost was around $270. I did not shop around for the best deals on the parts, and perhaps it can be done for less.

Here is a simplified pic of the wiring as it comes from the factory. I have omitted the circuits on the board that power the fans, and the thermostat connections, but they are not involved in this solution. I apologize in advance for my schematics. There are great schematics printed on the cover for the circuit board and in the SCS manual.

   

Here is my rendering of the concept.
   

Here are some important install notes.

I started at the power junction box that feeds the unit for my wiring. 
The circuit board will still need both hot legs and neutral to power the fans. 
If you have two units with two compressors each, the hot leg to the comp 1 and the hot leg to the comp 2 are reversed between the units, so that when on LOW both legs are loaded evenly. 
Do not reverse the common and hot legs on the circuit board.
In my diagram I used the common running from the junction box to the compressors on one side of the contactor coils instead of running common from the board back to the contactor. It just saves wire and makes for a neater install. 
I personally do not care for wire nuts when working on the AC system, for I have had numerous close melt downs due to them vibrating loose. I love the aluminum wire connector where each strand is individually tightened with a screw, or use lugs. 
I labeled the contactor boxes so that next owner will know what they are. 



This all sounds a lot more complicated than it actually is. And it is probably a lot of overkill.

[bikestuff]

Just to add to Richards writeup...for those that are reading along at home.

The thing that was not obvious (to me) is that *all* the current to run the compressor actually flows over the leads on the circuit board. Most of us think that circuit boards carry low voltage and low current. That is not the case in these AC boards. They carry and switch high current and high voltage.

I have implemented Richard's fix and it has worked well for several months. I am no longer worried about the board having another melt down.

One last thought. There are fewer and fewer of these boards out there in the wild. They are no longer manufactured. If your board has a catastrophic melt-down it will probably not be repairable. So, in the future we may be in a situation where an AC unit will not be able to be repaired.

Like my high school chemistry teacher (Mr. Harris) said ...."A word to the wise is sufficient"

[kenstruks]

Richard, are the c1 & c2 going from the board to the control box 24v ? thanks

[ashley]

All that I am about to explain and recommend is not new or original to me. I do believe that @"RussWhite"  was an early identifier of the inherent weaknesses of the circuit boards in the SCS air conditioners. So I am repeating what I have learned from other gurus and how I went about hopefully solving the issue. I will admit upfront that the solution is like killing a fly with a tank but Rhonda does not tolerate heat due to a heatstroke years ago. AC is very important to her, and therefore me.

The problem is that each of the two compressors in the system pull around 15 amps on a hot day and they run almost continuously. That doesn't include the surge amperage either which adds to the issue each time a compressor starts. The circuit board apparently does not have the robustness to carry that kind of current. There are three known problem areas. The first is the "lands" or the silver lines on the board that conduct the electricity are not heavy enough to withstand the current. The second problem is that the plug where the compressor wires attach to the board is not heavy enough to carry the current. The third is that the relays on the boards that engage to power the compressors do not last forever running that much current.

All of these problems are compounded with low voltage or loose connections in the wiring which raises the amperage even further. Low voltage/ high amperage will cook the board if you are lucky, and cook the compressor if you are not.

Some have been successful in soldering wire on the back of the board to help carry the load, and I think the new ones come from Newell with the wires already added. Some have replaced the compressor plug with a soldered connection. And some send the boards out to have the relays replaced.

All of that to get the the overengineered solution.  This solution is simple in concept, and not too hard to implement if you understand basic AC electricity. The concept is this. Snip the wires that would normally feed hot and neutral to the compressors. Use snipped end on the circuit board side to trigger an external heavy duty motor contactor. Power the compressor from the contactor by connecting the snipped ends on the compressor side to the contactor. So instead of the circuit board turning on the compressor and pulling 15 amps through the board for each compressor, the board merely turns on the contactors. The contactors pull about 0.25 amps. The load on the board is now reduced significantly. The board will still power the fans which pull around 2 amps each, but this solution takes around 14 amps off each side of the board.

I used 30 amp definite purpose contactors and mounted them in a remote box outside the unit on the wall above. The contactors were about $25 each from McMaster, the boxes another 20 each, and wire and connectors probably another 30. The total cost was around $270. I did not shop around for the best deals on the parts, and perhaps it can be done for less.

Here is a simplified pic of the wiring as it comes from the factory. I have omitted the circuits on the board that power the fans, and the thermostat connections, but they are not involved in this solution. I apologize in advance for my schematics. There are great schematics printed on the cover for the circuit board and in the SCS manual.



Here is my rendering of the concept.


Here are some important install notes.

I started at the power junction box that feeds the unit for my wiring. 
The circuit board will still need both hot legs and neutral to power the fans. 
If you have two units with two compressors each, the hot leg to the comp 1 and the hot leg to the comp 2 are reversed between the units, so that when on LOW both legs are loaded evenly. 
Do not reverse the common and hot legs on the circuit board.
In my diagram I used the common running from the junction box to the compressors on one side of the contactor coils instead of running common from the board back to the contactor. It just saves wire and makes for a neater install. 
I personally do not care for wire nuts when working on the AC system, for I have had numerous close melt downs due to them vibrating loose. I love the aluminum wire connector where each strand is individually tightened with a screw, or use lugs. 
I labeled the contactor boxes so that next owner will know what they are. 

Thank you so much Richard

This all sounds a lot more complicated than it actually is. And it is probably a lot of overkill.

[bikestuff]

Ken,

The triggers for the external relays are driven from the old 120V wires that used to drive the compressors.

So, without disturbing the board itself, the connections and wires that were used to drive the compressors are now removed from the compressors and used to trigger a pair of external relays which have an inputs from the same AC that supplies the board and outputs that go to supply the compressors. (Clear as mud, I know!)

I am not aware of any 24V in this system.

Bill