My parents live in middle Tennessee in a house that was built in the mid 70's. The house use to have electric heat with no A/C but then a new unit was installed in 1996. All of the duct work is in a crawl space.

The unit is a 3 ton 1996 Coleman packaged heat pump with electric back-up heat. The house is 1 story. I was visiting them back in October and I noticed some strange things occurring from the heat pump when it starts up. Sometimes when the system turns on, It sounds like the unit tried to start, but failed, and the only thing that turned on was the blower. Then a few minutes later the compressor and fan motor finally turn on. I checked the thermostat and it said heat on. I went out to check on the unit after it turned on one time because the air was not warm coming out of the registers. All I heard was the blower. The weird thing is, the system doesn't act like this all the time. The unit starts up normal most of the time. I told my parents about it and they did not seem to care too much. I visit them yearly since they are in their low 70's. In the end of next week, I'll be visiting them again. They have had the unit service 3 years ago. I did tell them to call a service tech out and they said they would, but the last time I talked with them on the phone I asked if they called the tech and they said they haven't.

What could be causing the unit to start up weird? I was thinking the contactor or capacitor, but I'm not quite sure.

Thanks in advance.