Frozen heat pump for 1st time
If you did not properly wire the cap (start/ run) your motor may not be spinning at the correct speed if it spins up. 
Frozen coils are more often when the defrost is not properly cycling. 
Depending on the brand it could be time based, but more often is pressure based (with Refridgerants temps = pressure)  you could have caught it just prior to when it was going to start a defrost cycle. 
The reversing valve could also not be functioning correctly. 
More info on why you changed the cap may give us the information needed to help you.