Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.
You really wouldnt want to condemn the pressure switch until you actually measured the vacuum and compared it to the setting of the pressure switch itself to make sure you dont have a slight flue blockage, slow inducer or something. That is to say, if it's a drop in vacuum, the pressure switch wont help.
You would use a manometer or a magnahelic to measure the vacuum and I would expect it stay about 0.2" above the setting of the switch or more throughout a run cycle.
the 5000 is a series, do you have an actual model number
On some condensing furnaces, if the drain is slow, it can open the pressure switch.
Tempstar is an ICP product so you may find the part locally if you know of a Heil, Arcoair, ComfortMaker or Keepright. Since ICP was purchased by Carrier
, you may find it at a Carrier distributor but I wouldnt try that first.