Bar-line commercial ice machine stay on defrost when I turn it on

You will need to replace the "defrost thermostat" on the unit. Here is the kit to order.

On Hoshi ice maker, if coils are HOT, it is passing hot gas from compressor into the lines. After the defrost of the first cycle, after this cubes are completely cleared from the plates, the "Hot Gas Valve" should close and the freeze cycle should start over. It sounds that the valve is sticking open and not stopping the hot gas from entering. Look there first.

need model number to really help. generally, if you turn on the number 1 and 2 dip switches on the control board, it will give you the longest possible defrost.

Ice makers defrost is the harvest cycle. The purpose of a defrost cycle is to clear any ice build up, right?

when the machine first starts, it begins it's cycle in the harvest mode. If the float switch is stuck, it stays in the fill/ harvest mode. Compressor runs and water circulates but no ice is being made. I'd start looking there. Turn the machine on, let it run for about 3 minutes, they very lightly tap the float switch. If it starts making ice, bingo, theres your problem. Let me know if I can be of any more help.

several things cause freeze ups.
If you have water filters on the water system, be sure they are not restricting the water flow. water flow pressure should not go below 20 psi.
The bin stat may not be shutting off the unit properly. It should shut off machine within 10 seconds of ice making contact.
Make sure the float switch is not dirty. Be careful when cleaning. Fragile
Make sure water pump runs the entire time it is in the freeze cycle.
Be sure the evaps are clean. Ice cubes will hang on if not clean.
Water solenoid has a screen where the water line screws on to it. Turn off water and check screen to be sure it is clean. This can restrict water flow.
Make sure water valve closes all the way. Turn machine off and see if water is still running. Valve may be leaking water thru.
Dip switches on the board, #1 and #2. Turn them both on and it will change the defrost time to 3 minutes. If both are off, they are set on 1 minute.

Hope this solves your problem. Let me know

The defrost cycle is a set time. I would suggest cleaning the evaporator so it has less chance to hang up in the trays.

This is the safety telling you it is staying in defrost (Harvest) cycle for more than 20 minutes. In most cases it's either a low freon level or a back head pressure device commonly called a "Head Master". Needs to be checked out by a trained tech. Not a simple fix.
Hope this helps.

seems that its low on water or float switch is bad. try to clean float

I am guessing there is a safety switch somewhere which is gauging how much water is left in a defrost tray. Other likely things: open circuit breaker from the water shorting things out. Start with these. Other, more exotic things could be involved...but not as likely as the above.