I have a Goodman package unit. I have a new run capacitor, transformer, T-stat and thermostat wiring but the unit will not come on. I can get it to come on by touching the contactor on the outside but not by the t-stat. Does anyone have an idea what could be causing the problem?

check where the 12 volt wires connect together
before the contacts

First off the system works on 24 volts not 12 volts. just because you put on a bunch of new parts it does not mean the unit will automatically run.

First there is a wiring diagram on the inside of the service access door on the outside unit. It should show you how the wiring has to be attached. This is a exacting job with no mistakes. Once you have checked that all over then you neew to take a meter and teat to see if you have 24 volts on the low volt side of the transformer and if not you will need to check the high volt side of the transformer for 220/240 volts.

Do those things and post back with the exact results.
NOTE you are playing with high voltage on one part of this test. Use caution sense 220/240 volts can kill you.

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