I checked the low voltage on the yellow wire and it is good going to a pressure switch, but nothing comming out. I ohmed the pressure switch and it was open. The yellow wire goes to the pressure switch then to the timer then to the contactor. I didn't have voltage to the contactor. Is the pressure switch bad? The outdoor fan is running, but at a slow rpm. If I push in on the contactor, the fan speeds up. I can't tell though if the compressor is kicking in. I by-passed the pressure switch and connected the yellow wire to the timer. I turned the power back on and set the t-stat to cool. The contactor energized and the fan speed increased quite a bit. I went inside and felt the air temp from the register and it is not very cold. Any ideas?