Lights blink/dim

I have a TRANE 5 ton heat pump which causes the lights in the house to dim when it kicks on. Is this a simple service or the heat pump is ready to die?

Probably normal.....a 5 ton unit has a humongous startup LRA, so almost any home would possibly see lights dimming as it starts. ( The LRA is quite likely in excess of 150 amps)

If it seems way beyond momentary, you could have an electrician check it out.

Ask your AC contractor if you have a Hard start kit on your outdoor unit. A factory hard start kit will help your compressor get up to speed faster and reduce but may not totally eliminate the dimming. There may also be conditions in your electrical system that could cause this. A qualified AC and/or electrical company would help determine this.

Check for any loose "neutrals" in your electrical system.

Momentary dimming is considered normal,........and as others have said, is due to quite high LRA "Locked Rotor Amperage".
It should only last a second or less.

If your unit is not set-up for hard start with a start capacitor, and relay,........you MAY reduce the dimming by adding a cheap aftermarket hard start kit.
They simply hook across your run capacitor terminals.