I have a Carrier Weathermaker SX furnace with a Carrier heat pump with propane backup. I've had problems over the last few years with the heat at the beginning of the winter season. Both the heat pump and propane have issues. I've had it serviced several times by a local HVAC guy but he can't seem to permanently fix the problem or determine what the problem is. It somehow seems to work (sometimes) after he works on it, usually after a couple of service calls in a row. He is recommending replacing the heater but can't tell me why other than a blanket statement that the heater is old---it is 19 years old, Model number 58SX120-LG-1, Series 190. The HVAC guy replaced the programmable thermostat that I put in a few years ago with another programmable thermostat saying that the one I had used was incompatible(even though it worked fine for a couple of years)a while back and maybe it's coincidence but the heater seemed to develop more issues after the replacement. I have little confidence in the HVAC guy but am not sure if it makes sense to bring in someone else because maybe I am reading too much into this.
What the heater does: When the thermostat is first turned on to the "heat" position, the heat pump starts and heat comes out---this lasts for several minutes and then a clicking sound can be heard both at the thermostat and the furnace and the blower continues to run but the air is cold and the heat pump shuts off. When I engage the emergency heat at thermostat, the blower starts, a clicking sound is heard, but the burners do not ignite.
Any advice? I tried to find a service manual online but have not had any luck yet. I am mechanically skilled but not great with electronics, although I have had significant experience trobleshooting CNC machines in a maufacturing environment.