There are times when the attempt to do something positive can result in something unexpected or unforeseen. The annual increase in the number of hard-start kits being added to air conditioners is a perfect example. Hard-start kits are being installed by contractors for a variety of reasons: extending the life of an old compressor, reducing starting amperage, and lowering the load on the utilities; etc. 

Utilizing a failed (that is, “open”) motor-run capacitor as the basis for our “Destructive-Analysis” experiments led directly to the failure of a number of our test compressors.  That is, once started, a compressor will run without a motor-run capacitor.  Compressors were never meant to operate without a motor-run capacitor. The problem will occur because the hard-start Kit will briefly replace the failed motor-run capacitor thereby allowing the compressor to restart.  In our experiments, we’ve seen the compressor quickly overheat, with surface temperatures reaching as high as 213.8­ ºF and refrigerant pressures as high as 700psi.  While the compressor’s own internal protective devices attempt to protect the compressor, the repeated restarts are what destroys it.

Past and current designs have the wires from the hard-start kit connected to the same motor-run capacitor terminals that are wired to the compressor. In these designs, the capacitor terminals are acting like terminal blocks.  With the large “boost” of capacitance from the hard-start kit, definite compressor failure will occur after an extended time running without the motor-run capacitor, accompanied by the repeated hammering the motor takes from “high-boost” over-capacitance starts.

AmRad Engineering recommends the new Patent-Pending Motor-Run Capacitor with Compressor Protector Terminal.  The new design for the Turbo series capacitors has a separate terminal specifically for use with any hard-start kit. This terminal is connected internally to the common terminal and will completely separate the hard-start Kit from the compressor upon a motor-run capacitor failure. This will save the compressor because the hard-start is no longer in the circuit to allow the compressor to restart.

Publication date: 5/27/2019

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