Carrier Stealth, won't cycle on/off

I'm trying to help a friend with his Carrier Stealth.

The unit is set for On/Off operation but won't cycle correctly. It'll pull down below the set point, go into heat mode, warm up the box before repeating the cycle.

From the controls, it will seeming correctly set for either Continuous or On/Off but the unit runs continuously.

Any idea where to start?

Are there any electronic copies of the operators or setup manual?

Many thanks!