My house has 2 - 2 ton Trane heat pumps with Honeywell thermostats... they are about 10 years old and work very well. About 8 months ago one of the units started short cycling... very short on-offs, just of the fan unit the outside unit does not turn on when it does this. I had a HVAC contractor look at the unit and he seem to think that everything was fine. I have started paying more attention to it and it seems to only happen in the morning and evening, and it happens in both heating and cooling modes. The therm will be set to 70 and it displays 70 then the fan unit will switch on-off in very short cycles <1 sec. Sometimes 2 or 3 times sometimes more then it will stop... then some time later when the therm goes down to 69 the outside unit turns on then the fan and it heats or cools fine... the therm reaches 71 and the unit shuts off. I pointed this out to the tech and he explained that this is sometimes a normal operation... I don't believe this. The other unit does not do this! I think that this is an issue with the therm's hysteresis... can someone help me out?