cat 922B wheel loader cab heater troubleshooting

I have a mid 1960's (not exactly sure what year) cat 922B wheel loader with a 3304 diesel engine, the machine has a small heater in the cab to the right of the driver that looks to be hooked up to the radiator coolant hose's. It appears to have an inlet and outlet hose going to it with some electrical wiring hooked up to the top of the unit. The heater is not working and appears to have no coolant circulating in or out of the the two rubber hose's, I have a single wire that connects to the top outer shell of the heater which has power going to it and I have another wire that goes into the back of the unit. Where do I begin to start troubleshooting the heater to find out why it's not working, could it be an electrical or mechanical issue that I could test to find the problem, any help would be much appreciated.

Hi Dan,

I would start by following the hoses back to the engine and look for a shutoff valve. It could be somewhere near the water pump.

Next thing would be to check the electrical circuit with a test light. Look for the switch. Check to see if you have a complete circuit and if not where does the flow of current stop?

If you can, take a cover off of the heater to access the fan motor(s). Then test current to the motor. It could be brushes worn or sticking in the motor.

That is where I would start, hope that helps.

Sounds like the same heater as the one in my 922A. Simply a heater core with a small squirrel cage fan. It probably has a 24V fan motor. Check water flow as stated. If the core is warm you have water and then it's down to if the fan is running or not. Mine is a single speed fan with just a hot and a ground wire. I often have to tweak the switch a couple times to get it to start. Another spring project to replace.

Edit, The on/off switch for the fan motor is mounted on the heater on mine.