Mechanic - Compressor Short Cycling??

Problems related to residential installations.

Mechanic - Compressor Short Cycling??

Postby DThomas » Wed Jul 06, 2011 8:08 pm

What is the problem when the compressor stops running, condensor fan stops running, and your contactor stays engaged?
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- Mechanic - Compressor Short Cycling??

Postby nomadpeo » Wed Jul 06, 2011 10:39 pm

first thing that comes to mind is the dual capacitor. this is a canister with two capacitors inside, one for the compressor and one for the fan motor. typically, if it fails, both will fail and both motors will overload. if this is the case, both the fan motor and the compressor will be hot to the touch. each has an internal thermal sensor which opens a switch in series with its motor winding. once cooled down, it will reset and the motor will try to run again. these are psc motors and will not run without the capacitor. therefore, they will overload and heat up very quickly each time they reset.

most modern units now utilize dual capacitors, as opposed to one separate one for each motor. it is a common occurence and it's not unusual for a technician to replace dozens each summer. sometimes they just fail due to normal heat conditions, but usually when a component fails, there is an underlying condition that caused it to eventually fail. maintenance issues are usually the reason for these types of failures. it is best for you to have a tech come out and diagnose the problem. if he says the compressor is out and you need to replace your unit, get a second opinion. if both motor and compressor are kicking out, it's a capacitor or a fan motor. while he is there, have him clean your condenser coil and check your freon level. also have him check the return air and supply air temperature. have him show you the readings and subtract sa from ra. this number should be no less than 16 and no more than 20, ideally 18. look at the RLA (running load amps) rating on the name plate of the condensing unit. have him tell you how much current the compressor is pullling. ask questions and get answers. keep him on his toes and let him tell you what he's doing for you. if he doesn't like it, don't use him, but don't try to fix your unit yourself unless you are trained.
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