Last weekend my son and i took a short, cold drive to town and discovered we have a very inadequate amount of heat in the car.After doing several searches in the forums for a problem i'm currently having I've come up with a list of troubleshooting steps of what i've done and what's still left to do so i wanted to run it by the crowd in case i missed something.

Heater core plugged? Common problem, cause we don't use them they fill up with gunk. Pull the core and flush it out. Mine works MUCH better after the cleaning.

I'm hoping it can be done in the car w/o pulling it ? I was going to pull the hoses from under the hood to backflush. If it needs to be pulled, how hard a job is it ?

It's a heck of a lot easier to pull the hoses off the engine than to pull the core, I think.  I'd back flush it through the hoses.  I'd also go back and see if you get warm air in the cockpit when you pull a vacuum on the valve.  If you do, then you don't need to back flush, just find out why there is no vacuum to the valve.

I have a 180* thermostat with my DeWitts, and it rarely goes above that except in the summer with the a/c on.  In fact, I'm wondering if I mistakenly put a 160* thermostat in it.  Hell of a radiator.

hi    I don't know how  much  water pressure have   but keep it low to flush heater core  use only water  if something is  in core  it will come out  just use water  not high pressure and check heater control valve  rs of engine   by exhaust manifold   make sure this is opening    take your time  let us  know     dwa175

Without knowing your history with  the car this post may be useless but there is another possibility.  It is fairly common to install a manual water cutoff valve in the water lines going to the heater core. This is done to completely shut off the hot water to the core during summer.  Mine are hidden in the lower part of the hose under the car and out of sight. If you haven't already checked, make sure there isn't a valve somewhere that is closed and preventing hot water from getting to the core.

The vacuum line that goes to the factory vacuum water shut off on my 82 comes through a 3 port grommet in the firewall near the distributor and feeds from a plastic valve mounted under the dash just above the glove box.  I had to replace some of those vacuum lines to get my factory valve to function properly.  The plastic valve gets its vacuum from a "T" in the line near the brake booster, yours may be different.  Hope this makes sense and helps you troubleshoot.

I have a manual shutoff in my heater hose as well because the 72 didn't have the vacuum valve.  Heater core was always hot.

Thanks All for the suggestions. I did check for a manual valve inline and there are none there. now that i understand when vacuum should be there and what it does it will help to troubleshoot. I've been called to go out of town for work, so it will be a couple weeks before i can report back, but it's now top of my to-do list ! I'll certainly respond once i get this done !

Well..IF you have no vacuum to the in line solenoid in the heater hose..It is quite possibly the temp control cable that runs R/S of console from the master hvac mechanism to a BYPASS water shutoff valve that resides behind the glove box.The bypass does several things..When you switch to cold with A/C OFF it transitions mechanically AND vacuum wise to supply vacuum to shut the solenoid in the heater hose And..OPEN air duct vents for the other options on hvac..that bypass switch when temp is moved from OFF/COLD opens the hot water that provides def/heat..or just vent from outside.The cable has a turnbuckle that is used to get the adjustments so the temp control lever changes the MODE for the hvac..

|UPDATED|7/18/2016 9:21:54 PM (AZT)|/UPDATED|