Need to replace Thermostat
My 2001 used a mercury bulb thermostat. I replaced it with a digital Hunter that I bought from Walmart. Cost was less than $20 back at that time. Thermostat was a great improvement over the factory installed unit. Like my current Classic the thermostat was installed on a wall that was common with the refrigerator compartment. The hole for the wiring passes into the compartment which leads to air leakage. Especially if you operate the bathroom vent or stove vent fans. This leads to frequent cycling of the HVAC equipment. Be sure if you replace the thermostat to make sure that hole with the wire is sealed. I used a dab of silicone to help. Note that my Hunter did have an adjustment to control the spread in which the thermostat operates with. Some call that the maintenance band. This allows you to adjust up and down, the threshold in which the thermostat calls for heat or cooling. This allows you to compensate if the equipment is activating too quickly.
'04 Classic 30' S.O.,'03 GMC Savana 2500,'14 Honda CTX 700