It is goodman gmp050-3. the red light blinks 3 times. I have replaced the pressure control switch and the thermostat. But still no change. Could I have gotten a bad pressure control switch. What else could it be? HELP

http://www.hvacpartsshop.com/Gmph075-4%20Series.Pdf

This is a complete Goodman service manual. Only use the parts of the manual that pertains to your model number. This is the same professional manual the factory Goodman trained technicians use. Now you can look up your problem test the part and solve it.