09-01-2018, 07:07 AM
A Foretravel Forum member has a unique basement A/C system on his older coach. His board is fried such that a board rebuilder has pronounced it un-repairable.
The following was posted in response to his request for help and ideas. Hope you all will find it interesting if not indeed helpful.
"Tyler, I owned a commercial HVAC company for years. We serviced transport refrigeration as well. I am (unfortunately) very familiar with overly complicated control circuits.
Basic AC systems are very simple. First, the components have to work; meaning the compressor has to run and compress the refrigerant, the condenser fan (outside) has to run and move air, and the evaporator fan (inside) has to run and move air. The compressor will have capacitor and/or a potential relay that will fail. The fan motor may have one as well. These can and should be checked and replaced if needed. I usually replace them anyway since the get weak with age, are inexpensive, and will fail at the most inopportune time.
Next you need a control circuit. The simple circuit is a contactor (relay) to actually connect 120V to the components upon demand, and a thermostat to control to contactor. Typically, the compressor and the condenser fan are controlled by one contactor and the evaporator fan by a second one. This allows the evaporator fan to be on for circulation without cooling.
In your case, I would buy one double pole 20 amp contactor for compressor and condenser fan, one single pole 20 amp contactor for second compressor, and one single pole 20 amp contactor for evaporator fan. All should have 12V coils (for control voltage). You then need a 2 stage cooling battery powered digital thermostat. You will have to pick up 12V to power the control voltage circuit. You have the original wiring schematics so that should not be a problem. Once installed, you have a simple control circuit with readily available components.
TOM"
The following was posted in response to his request for help and ideas. Hope you all will find it interesting if not indeed helpful.
"Tyler, I owned a commercial HVAC company for years. We serviced transport refrigeration as well. I am (unfortunately) very familiar with overly complicated control circuits.
Basic AC systems are very simple. First, the components have to work; meaning the compressor has to run and compress the refrigerant, the condenser fan (outside) has to run and move air, and the evaporator fan (inside) has to run and move air. The compressor will have capacitor and/or a potential relay that will fail. The fan motor may have one as well. These can and should be checked and replaced if needed. I usually replace them anyway since the get weak with age, are inexpensive, and will fail at the most inopportune time.
Next you need a control circuit. The simple circuit is a contactor (relay) to actually connect 120V to the components upon demand, and a thermostat to control to contactor. Typically, the compressor and the condenser fan are controlled by one contactor and the evaporator fan by a second one. This allows the evaporator fan to be on for circulation without cooling.
In your case, I would buy one double pole 20 amp contactor for compressor and condenser fan, one single pole 20 amp contactor for second compressor, and one single pole 20 amp contactor for evaporator fan. All should have 12V coils (for control voltage). You then need a 2 stage cooling battery powered digital thermostat. You will have to pick up 12V to power the control voltage circuit. You have the original wiring schematics so that should not be a problem. Once installed, you have a simple control circuit with readily available components.
TOM"
Rudy Legett
2003 Foretravel U320 4010
ISM11 450 hp Allison 4000R
Factory Authorized Aqua Hot Repair Center
Southeast Texas Area