I have my thermostat set at 78 degrees, system turns off before it reaches temp, I turn to off and back on again two or three times to reach desired temp. When it reaches desired temp, it drops to about 70 -71 degrees before it comes back on. How do I set it so that it doesn't drop that low. I don't have a manual, I just have the thermostat cover for instruction. My email is diboll62@yahoo.com