Never ceases to amaze me how many hvac techs have a total misunderstanding of ac power, and how incorrect opinions are foisted off as wisdom, must be a gross error in some hvac text somewhere? .
1. good news - everyone is correct in that the caps should be rated at 440 Vac for good reliability.
2. bad news - not a single poster seems to understand ac power flow. The 389 or 400 V across the cap IS NOT generated by the start or run winding. The voltage across the cap plus the voltage across the run winding is exactly equal to the line voltage at EVERY specific point in time. When you hook up your digital voltmeter, you are probably reading 1.11 time the average voltage ( any cheap meter, even a Fluke 77 reads 1.1 times average vs true rms). If you hook up a scope (e.g. Fluke 123 or equivalent) across the cap and run winding, you would see that at times the volts of the sine wave across the cap is negative and across the winding is positive and both are higher peaks and rms than line voltage - read up about leading and lagging currents in capacitors and inductors before blathering about back emf, etc. and about resonance and voltage amplification thru resonance, etc. etc.
[Edited by junkhound on 06-30-2005 at 12:23 AM]