ptac unit losses heat in coil

michael tierney

I have a 2'steam riser with a 3/4' return line feeding 4 coils on the 3rd 4th 5th & 6th floors of a high rise building.Using a vacuum system and with a return steam temp of 150 degrees up to 160 degrees and vacuum of 10' to 15' i still loose heat at the 5th floor coil every couple of days. I have changed all 4 traps and also changed all 4 coils but still this problem persist and can occur it seems even when system is working perfect. Any ideas on what could be causing this.