AC Repair Thermostat won't call for cooling

One subscriber has a problem with their new thermostat let's see if this helps
new thermostat

installed new white-rogers manual thermostat. everything works fine, except ac compressor will not come on.
If you have a wire hooked to the Y terminal on the stat then you need to follow that wire through the system when you have a call for cooling the thermostat closes or sends a signal from the R terminal on the stat which has 24 volts ac to the Y terminal, from the Y terminal the signal goes to either an indoor air handler(gas furnace, electric furnace, I'm not sure what you have) or to an outdoor package system the signal on that Y wire, depending on manufacturer may have to pass through a number of safeties before it tells the compressor contactor to close.
Here is how I do it, Turn main power off to the system then take the thermostat off the wll and tie the R and Y wires together turn the system back on then if your outdoor unit doesn't run you know the problem is not with your tstat then either put the stat back together or leave it jumped out and look for that 24volts the first place to look is at your air handler or furnace where the R and Y wires come in you need to check if you have 24 volts from the Y wire to ground or the neutral on your transformer if you have it there then you need to check it at the outdoor unit if you have 24 volts coming into the outdoor unit then the problem is in your outdoor unit follow the control voltage all the way through some manufacturers have low pressure safeties to protect against refrigerant loss and high pressure safeties to protect against dirty coils or a bad fan motor just follow the control voltage through the system when you find a spot where you don't have 24 volts then you know that is where the problem is if you get stuck just let me know