Cleaned AC system, heater not working anymore

My AC compressor was seized for a few years, so I removed and cleaned the entire system before installing a new compressor. Now my heater is not producing heat. Everything else works, including the AC, but now the heater is not producing heat.


Any ideas as to what could be the problem? How I could check if the core is working?

Thanks!

 

the heater works off of the water pump and there should be a valve that sends water through it when you call for heat. the heater core is just like a radiator and the valve may not be opening or the core may be blocked up and not flowing water.

try disconnecting the heater hoses and run water through it in the opposite direction to flush it out.

in thre center of the firewall there is a little black box with a rod that opens and closes the valve to send water through the heater core, make sire its working, on some vehicles it works off of vacuum but on our first gen trucks its a simple cable operated lever so have someone move the control while you confirm the lever is working and it isn't disconnected. in the past on older trucks, if you didnt use antifreeze, the paddle inside this valve that stops the water flow will rot out and water will go through it all the time running the heater 24/7 making people think the a/c was broken but I think they are all made of plastic now to prevent that but sometimes if the a/c is cooling right this heater valve not working correctly might be the reason.