Yes there is reason to keep the crankcase heater energized. Its purpose is to prevent migration of liquid refrigerant to the sump of the compressor which can do damage to the compressor on start up. Refrigerant will condense into a liquid in the coldest spot of the circuit and the lower pressure resulting from the condensation to liquid will cause more refrigerant vapor to take its place. This migration and condensation will continue until there is a pressure temperature equalization. By artificially heating the compressor, you drive the liquid refrigerant out of that section of the circuit and reduce or eliminate the damage it causes on start up.
The crankcase heater is a purely resistive circuit so to calculate its power consumption use the power formula of W=IxE where W= Watts I= Amp draw that the heater is using E= the applied voltage.
A typical heater draws anywhere between 0.15 and 0.35 amps (measure yours to know exactly what it is consuming at that time). Assuming 230VAC applied supply voltage multiplied by the 0.15 to 0.35 amps gives you 34.5 - 80.5 Watts.
If it is NOT a heat pump then you can shut down the condensor for the winter if you want to; however, there will come the warm days that you will need or want AC for short or limited times and the Manufacturers always recommend energizing the heaters 12-24 hours before starting the AC cycle to allow time for the liquid refrigerant to be boiled off and the oil to be warmed up.
I would personally not mess with it considering the minuscule cost of running the heater versus the cost of not and then damaging the compressor. There are other ways to save pennies in electrical bills that do not have such costly consequences. The choice is yours though - a few pennies per day for sound and solid insurance for your machine or risking a few thousand dollars out of pocket (as an unexpected expense) for a compressor or whole condensor change out due to broken crank, bent valves, or oil loss/failure damage that the heater is designed to reduce or eliminate.
If your compressor DOES NOT have an independent crankcase heater at all (belly band or bullet style in a well) and all you have is a single pole contactor - one contact and the other side barred - then it is incorrect to believe that the windings inside the compressor are energized at all times and heating the compressor. Single phase motors (1 line of power in 1 line out) can be safely stopped by breaking only one line of power. You can break both lines by using a two pole contactor; however, the minimum is one leg/line/pole. The Manufacturers use single pole contactors as a production/money saving feature (they cost less per unit than installing a 2 pole - less cost = more profit to them and still does the job). In this case, with no independent crank case heater, you gain/loose nothing by leaving the condensing unit on. There is no current flow through the motor windings as you have broken the circuit ( if there was current flow you then would have an unintentional circuit and a defective/grounded winding(s)). No current flow means no cost to you.
Last edited on Mon Aug 3rd, 2009 10:12 pm by dkpd1581
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