Complete 1 system a/c repair and preventative maintenance check. Found system off on high pressure lockout. Dirty filter caused unit to go off on high pressure lockout in heating mode, customer realized unit wasn't working when he switched to cooling mode. Changed filter. Tested refrigerant pressures and they were good. Subcooling at 6.5 degrees, manufacturer specs call for 5-7 degrees subcooling. Changed filter for other system as well. Signed customer up for one system maintenance plan for main system and performed cooling maintenance.System is cooling at this time.