I have a 95 F-350 with PSD. Was having problems with engine not getting warm enough. Replaced thermostat (with OEM Motocraft), replaced coolant using the required additives. Engine now runs warmer, guage almost gets to "N" in normal on warm days and a little less on cooler days. I still have no warm air from heater. I opened the damper door manually on the heater core box, but did not seem to have any effect on it. Both feed and return hoses to heater core get hot, this should mean I have warm water flowing through the core should it not?

Any help will be appreciated, it's getting cool here.

 

You will not get any heat if there is no water
flow through core. When you refilled your radiator
did you have your heater on? Try refilling radiator again..,engine and heater must be running in order to fill radiator with correct
water level..,
Good Luck,
EBTE tech

 

If you have hot hoses going to the heater core you should have heat. I had this problem recently on my '94 and figured the core was plugged with dirty coolant.
first, make sure you have clean coolant at the proper level after a good flush. remember to squeeze your upper rad hose to get rid of all air while the engine is running and coolant is running through the rad. Coolant is runing through the rad if the upper hose is hot.
Check with your hand if there is something obstructing the damper door from closing- I recently thought i needed a new core but found that a pen had dropped down through the defrost duct and was keeping the door open just enough to blow warm, not hot air.
I couldn't get this access until I took the heater core out.
Good luck let me know how you make out.