I'm putting the AC back in next week and decided to try the heater just for the heck of it. It does not blow hot. Heater hoses are hooked up. Temp gauge registers around 160. Cool air comes out of vents. What could be going on? Thanks

 

What model are you working on?
Sounds like a vacume hose is off
somewhere.
Check the black bulb on the firewall
and also the one on the heater valve
on the intake manifold.

 

It is a 70 Cutlass. I did hear some hissing when I slid the lever over to hot. Thanks!

 

Then you have one loose under the dash.
Careful, there are several! A flash light will
be your best friend. My best guess will be
on the plentum, there are two diaphrams,
should be silver in color, 'metal', one on top
and one on the side if I remember right.
Set the parking brake with the engine running
and see if you can pinpoint the hiss.
It could also be above the selector bars as well.
They are a little like speggetti though, there are about
eight in a small metal wheel, this operates defrost, heat, vent...
Good luck.

 

Check the vacuum line that runs from the control panel to the coolant valve at the RH back of the intake manifold. If line looks okay, disconnect it with engine running, heater on hot to see if there is any change to heater temp. Also note if there is any vacuum from the hose.
In 72 the coolant valve was failsafe - vacuum was applied to CLOSE the valve to turn the heater off. I am gonna guess that 70 was the same..........
Let me know what you find...

 

With the engine running at 160*,is this hot enough to have hot air blowing?

The reason I ask,when the diesel trucks at work only heat up to 160* in the winter,you have no warm air blowing,the air is still cooler.When it heats up to 180-190 you start to feel the warmth.

 

160 should give you heat, I agree it's better with a 180 degree thermostat. It also depends on how cold it is outside.

 

Are you sure the heater core isn't partially or totally clogged? If little or no coolant is flowing through it, you certainly would get little or no heat.

 

Thanks for the responses. I will have to wait till next weekend to work on it again. I will check the vacuum lines first since I hear a hiss. Will keep you all posted. Thanks