[Milsurplus] 400Hz fan run(start?) cap help needed

[Tom Norris]

I have some gear with small 24 volt 400 Hz fans installed.  I had one of the fans seize - taking with it the fan inverter board - and have yet to find an exact replacement.  One replacement of the same series (Rotron AXIMAX2HT/990YH) I found was 48volt 400hz.  However, the capacitor specified for this fan is 0.68 mf, where the 24 volt cap was 12 mf.  

One option is replace the things with DC fans, and have found some with similar pressure and flow specs, but I'd like to replace the fan in one of these amps with something close to original so I can compare various circuit temps between the two types of fan. (I can place thermocouples all over the place and compare temps, fairly easy)

Any comments on running this fan at a reduced voltage?  What would you recommend for the cap value if ran at 24 volts rather than 48?