apparently you have heat pump that is almost 30 years old. if i were to guess, that would also be your problem. without a thorough going over its impossible to tell. it could be sticky contacts or faulty t stat. does the cooling side work ok?
"When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin
"Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington