Have a very old model MAC 1165 intertherm gas furnace.The pilot is lit.Main burner will not come on.I disconnected the thermocouple and pilot stays lit. Please advise!It is cold in Texas today!

I'd replace the thermocouple. It is relatively inexpensive, and easy to do. If it is bad, it will keep the main burner from lighting. If the valve itself is bad, it will be an expensive proposition, and you'd want a new thermocouple anyway.

Good luck,
WallyH

If the pilot stays lit with the thermocouple disconnected, you may have a non-100% shut-off gas control with a remote pilot safety device (usually what the thermocouple is connected to). Look for a reset button nearby. A faulty thermocouple may indeed be the origin of your problem.