Below is a tech sheet for the unithttps://drive.google.com/file/d/0BzIiBNwRIV4NMEZXcmRYQUVCVDg/view
You said you checked the heater relay.
Where did you check it?
Using Neutral/ground as the reference side on the meter can be confusing.
RY6 BLK should be 120 all the time.
RY6 BLU should be 0 volts when unit is off and 120 volts when unit is on.
But the above does not tell you that the heater relay RY6 is actually closing.
So BLK always has 120 on it as it is hard wired.
But if RY6 does not close when running it will still get 120 volts but this will be the other side of the line Red to Neutral a this will feed through the centrifugal switch on the motor and the heater components to RY6 BLU.
So if it closes you get 120 volts and if it does not close you get 120 volts and there is no way to tell with a meter if the 120 is L1 or L2.
Remove the wire from RY6 BLU and rerun the test.
Just cannot short to anything.
Now if you see 120 at the BLU connector you know that it is L1 voltage.
If the above checks out OK then odds are that there is a problem with the centrifugal switch on the motor re: it is not closing.
A way to confirm this is to unplug the unit and the two heavier red wires at the centrifugal switch and short them together, Make sure they cannot short to anything else or get caught in a moving part.
Then plug the unit in and give it a try.
If you get heat then the centrifugal switch is the problem.
Could be that the switch is bad or the mechanics that clos the switch have a problem.
NOTE: This is just for testing and the unit cannot be left like this as it is a safety hazard !!!!!