I had to buy a new thermostat for the house, running AC only (separate stat for heat). Bought a weekly programmable at Lowes and hooked it up. Ran fine until the stat no longer calls for cooling. When set point is higher than room temp, the fan unit shuts off fine. But the compressor/condenser unit outside will keep cycling. It'll run for a few minutes, shut off for a couple minutes, and continue.

Did I wire it wrong? I didn't think so, since it works correctly when cooling. But obviously something isn't right. Does it make a difference if the condenser unit is on a separate breaker?

ETA - new stat is a Honeywell 5/2 programmable, I think the model # is RTHL2310b. There were three wires on the old stat. I thought I got them in the right place, but maybe not.

Did the old tstat control both heat and cooling?

If so sounds like you need to remove the jumper between RC and RH

This stat was always AC only.

The thermostat thinks it is controlling a heat pump.  Figure out how to program it for AC only.

That was a good tip. There's a switch on the back of the stat for heat pump or regular operation. It was set for regular, but I switched it to heat pump and now it works fine. I guess something is wired funny, but it seems ta be working now.