Do not post a schematic, it is of very little help and somewhat redundant to a person that knows HVAC troubleshooting.
You should check to see if the 24 (26V) is present at the contactor coil in the compressor unit. Also check to see if you have 240V on the line side of the compressor contactor. If you have 240V on the line side of the contactor but, not 24V to the coil of the contactor, they you may have a stuck/bad switching relay.
Also, check to see if someone installed an add on pressure switch that needs to be manually reset.