I am a student in a commercial refrigeration program at my local community college, and I had a test tonight in my Electrical class that kind of has me stumped. I can't recall the question *exactly* (and of course I couldn't write down a test question during the test) but it went something like this:
Customer has a refrigerated case containing a TXV that has no equalizer tube or balanced port. What type of motor start components would you expect the compressor to utilize?
A. Capacitor Start, Induction run
B. Permanent split capacitor
C. Capacitor start, capacitor run
D. Centrifugal switch
I put "C", and asked the teacher after the test about this question. I said something like "I think I got it right, because the txv won't equalize and you need a large amount of torque to overcome the high pressure on the high side of the system (since it doesn't equalize). He said "yes, you're right". The thing is I don't understand *why* it doesn't equalize. I've seen units in the field that have been off for a while (down) and when I hook up my guages the pressures are equal, but I think that's due to most txvs I see having an equalizing tube or balanced port. But even if the txv didn't have these equalizing devices, wouldn't the suction line begin to get warm, which would cause the sensing bulb to heat up and exert pressure on the power head and actuate the piston in the txv...which would create a little orifice for the pressures to equalize???
Sorry for the long post...