Can't get hot air in any mode(defrost or heater). Hoses to heater box feel warm on firewall side. Could it be something simple as low on coolant? Temp control and heater/defroster appear to operating normal....any troubleshooting suggestions?

Thanks in advance

 

Heater core could be plugged up and not allowing water to circulate thru

 

The heater hoses should feel hot, not warm. I agree, the core might be plugged/restricted. Also make sure your blend doors are opening, as these cable mechanisms tend to hang up from old age.
You can look under the dash as you slide the levers to see if things are moving.

 

The hose coming from the intake manifold passes through a vacuum operated valve and then through the firewall The hose is warm on the incoming side, but not the other, where it exits the valve and goes through the firewall. Could this valve not be operating and allowing hot H2O into the heater core?

 

Hot on one side of a valve and cold on the other is a dead giveaway that coolant isn't running through it.
That looks to be the trouble maker, either the valve itself or the vacuum supply.

 

Still no heat. All controls appear to move their respective flaps/diverters, etc. Of the two hoses going to the heater core...one from the H2O pump and the other from the intake manifold( passing through the a/c vacuum operated valve)...I assume the one to the intake is the return line? If both are hot, does that mean the H2O is circulating through the heater core?

 

NO, if its been running for awhile the water will get hot in both hoses just because the rest of the water is hot.
Normally when the heater is on full blast ( FAN ON HIGH, TEMP ON HIGH) You can feel that 1 hose is slighly cooler than the other, That's only IF the heater core is not plugged. Simple to check, just undo hoses at engine and run water from garden hose thru.It should flow right thru, I would turn spigot on all the way though, might be too much pressure.

 

Where do you live?

 

I disconnected both heater hoses and ran a garden hose through in both directions. A small amount of contamination came out, but the water flowed freely in both directions. I'll assume the heater core then is fine, as there are no leaks either. I can see the diverter working for a/c or heat. I can only hear the opereation for the temp control and assume it's working properly. I'm starting to run out of patience(and ideas) for finding the fix. Any more thoughts?

 

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