I have a goodman a/c with electric heat strip (10kw) and vey recently it stated to turn off before reaching the set temperature. After a few minutes it will restart and run for a couple of minutes and then shut down again without reaching the setpoint. It always stops at 66 on the white rogers programmable thermostat. New filter and unit is very clean and only about 5/6 yrs old, any ideas, thanks.

It could be the thermostat more than likely

OR

It could be a defective sequencer or heating element safety in the furnace Less likely

Post the EXACT model number of your thermostat and I will try and look it up to see if there is a possibility of a problem.

The only number that I can find is directly under the W/R address on inside of cover and it say type 1F80-51. It has batteries which I changed twice but still maybe run 1-2 minutes off 4-6 minutes and recycle over and over but never reaching setpoint. Last year it did reach the setpoint or go maybe a degree over before shutdown so don't think its just a degree variance. Also if I turn it up it stays at the same temp; 66-68, 66-69, 66-70, etc

Could I replace this 1f80-51 with any of these mdls... 1f80-361 or 1f78-151 or 1f97-1277 and which would be the best, thanks

From White Rodgers

1F80-51 (http://www.white-rodgers.com/wrdhom/common/ptech/thermo/StatTypeNumber1f80.htm#Classic80Info) is an obsolete model number. Click on the model number for homeowner's manual and other information.

See here for info on your old thermostat

White-Rodgers - Thermostats, digital programmable, non-programmable, mechanical thermostat (http://www.white-rodgers.com/wrdhom/common/ptech/thermo/StatTypeNumber1f80.htm#Classic80Info)

I had a Clare furnace that had the same problem. Turned out the drain for the heat exchanger was clogged