I've been working on a Carrier RTU Model 50hjq014. First time found the contactor not pulling even though had correct voltage at contactor. Just touched contactor and it pulls in. I replaced contactor and it worked fine for about a month. Called back out same problem. Checked for loose wiring, bad ground (contactor 120v coil), pressure switches. Couldn't find anything wrong, but went ahead and tried another contactor. Works for about a month then same problem happens. Tried even replacing current sensing switches. And it happened again. Any suggestions would be appreciated, maybe Im missing some kind of stat or switch that is on the unit.