Duotherm rooftop air condtioner 1978
1978? Refrigerant is R22, is too expensive and is banned from sales in year 2020. If the refrigerant is low and needs recharging for whatever reason, chuck the unit, replace it or abandon it.
Is there power going to the compressor
Does the compressor feel hot to touch, then there is power to the compressor. Could be compressor is locked rotor or capacitor circuit is damaged.
If it is ambient temperature to touch, no power going thru the compressor, due to compressor contactor is not energized, or contacts are burnt open, or the compressor itself is open winding.
First I would check to be sure no wires are burnt into. If that checks out then I would check to see if the windings are open on compressor by killing power to unit and remove wires from compressor then check continuity between R and C then between S and C. If either is open then your compressor is out on over load and needs to be cooled with water hose until windings close. If all is good there then I would check the capacitor and possibly a hard start capacitor if unit has one and replace if either has more than a 10% loss of microfareds. If all that checks out then check to be sure you have a full 230volts between each C and S then between C and R. If so then use an amp probe on your start leg/wire during start up and see if the amp draw exceeds lock rotor amps.(usually found on compressor inspection plate) If so you have a bad compressor that needs replacing. If compressor was just over heated then be sure to check refrigerant charge once you get unit running as it may be low causing the compressor to get to hot.
Could be capacitor? Check it, see if it looks like it expanded.
If so replace. Use screwdriver and short terminals to ground before touching wires and obviously turn off power first!
SOURCE: DuoTherm compressor starts but will not continue to run
check condenser fan if running. it will make compressor comes on and off if broken
SOURCE: Compressor doesnt come on in a dometic duotherm
If this is a wall thermostat controlled unit, then check to make sure that you have power coming from the yellow wire on the thermostat when it is placed in the Cool/Auto High mode. If you do not have power at the yellow wire, then you have a bad thermostat. If you do have power, then remove the control unit from the inside of the AC and see if you have power at the Y terminal there. If so, when you turn the thermostat to cool, can you hear a relay clicking in the box? If not, then you have a bad control box. If the relay is clicking, you need to check the power at the compressor relay on the board. It has a black wire to one side and a purple (or blue) wire on the outgoing side. Check to see if you have 120V on the blue wire when the tstat is set to High/Cool. If not, then you need to bypass the freeze switch to make sure that is not the problem. If you do, then you need to go upstairs and check the start capacitor for OK. It is located in the side compartment of the upper unit, it has a small black relay on the top called a PTCR. These often burn out and will cause the compressor not to work. If that is fine, then you go to the top of the compressor to the thermal overload switch. See if you have power at both sides, if so, then you have a bad compressor. If not, then the overload switch is open and not allowing power to the compressor.
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