[cyberdelic]

I purchased my home in Spring 2013, and both the heating and cooling functions of my unit and my old school, basic mercury switch thermostat all worked fine. Last fall, however, I switched out the thermostat for a new, smart one. In the process I found that the unit and thermostat were 4-wire, but at some point there was a five wire setup (the bare blue wire):

I happened to take a picture of the wiring on the old thermostat (I threw it out over the winter):

When I hooked up the new thermostat I ran the bare blue wire to the transformer in the unit so I would have common line:

I hooked up the new thermostat:

I've been pleased with the new thermostat, and it worked great on heat all winter. Now that the weather is turning warmer I've tried the cooling only to find it doesn't work. I can hear the thermostat click when it tries to activate the unit, but neither the compressor or fan seem to cut on. I can immediately follow up testing the cooling by setting the thermostat to heat, at which point both the unit and fan come on.

At this point I've exhausted my knowledge. I'd like to test the unit separately from the thermostat, presumably by briefly tapping the wires at the thermostat together to trigger cooling. Would that work? Which wires would it be?

Note
I just noticed the wiring on the old thermostat shows a couple of spots in which some things where jumped onto other connections. In particular, it looks like RC was jumped to RH on the old thermostat. Could be as simple as doing the same on the new thermostat?

 

[roughneck]

If this is a packaged unit just put a jumper wire in between RC and RH

 

[r0ckstarr]

I just noticed the wiring on the old thermostat shows a couple of spots in which some things where jumped onto other connections. In particular, it looks like RC was jumped to RH on the old thermostat. Could be as simple as doing the same on the new thermostat?

Look at the diagram on the top right of your last pic. You have no jumper. Simple fix.