Hello all, I live in Sacramento, and the temperatures are rising quickly! I recently turned my air conditioning on after months of the cold season, and it started making noise when the AC is running. It almost sounds like someone is walking on my roof. Any help would be much appreciated! thank you

Hey everyone, I've learned a lot from this forum already, but I'd appreciate some help regarding my A/C issue. I'll try to keep it brief. [list] [*]Thermostat calls for A/C, but neither compressor nor fan engage [*]With thermostat in "off" position, control board has 24V on R terminal and 0V on other thermostat terminals [*]When thermostat calls for "cool," none of the thermostat terminals on the control board hold voltage [*]Control board is fused with a 5A ATO fuse that is not blown [*]Transformer is protected with an attached circuit breaker. Transformer reads 240V and 28V on respective coils [*]Contactor is new. Compressor runs as normal when contactor is manually depressed. [*]Circulating fan operates independently when green and red terminals are jumped [*]Compressor doesn't kick on when yellow and red terminals are jumped [/list] A little extra background: I've been chasing this issue for a while. I'm beginning to think it was, initially, two issues. Now that I've replaced the thermostat (one problem), all signs seem to pointing to a 24V short somewhere; likely between the control board and the thermostat. I've not been able to test end-to-end resistance .The bad news is the routing of the wire makes it inaccessible, so I can really only test at the thermostat and at the control board. I can, at least, verify that the wires don't have continuity when disconnected at each end. I'd likely just have to snake in a new set of wires rather than seek out the short, but I just wanted to solicit the opinions of those more knowledgeable before I go on a fool's errand. HVAC is a new world for me. What do y'all think? Am I missing something obvious here?