Age of Tappan A/C Unit

Does anyone know the age of a Tappan package A/C unit? The serial number is 78 J 20369 FK and the model number is PHR-30-43-T. I was thinking 1978 but the house was built in 1980. Any help would be appreciated.

I get Oct. '78, 2- 1/2 ton unit. May of been used or sitting in a dealers warehouse for awhile.

September 1978. Skip the letter “I.”

Packaged units do tend to sit around in the warehouses longer than split systems.