My 1971's Heater Panel reads ...

AIR

Off --- Vent --- Heat

TEMP

Off -------------- Heat

DEF

Def ------------- Room

I didn't realize there was a difference and I bought one the reads ...

AIR

Off --- Vent --- Heat

TEMP

Cold ------------ Heat

DEF

Def -------------- Floor

Can anyone explain?

Although the words are different it seems that their meaning is the same.

Can I use the one I bought in my place of the old one?

Sounds like you bought a 73 HCP.

The differences between the wording is essentially Null.

Cold vs Off is due to the Water Valve being completely turned off and hence it will not warm the air rushing through it.

Room / Floor was probably because the inside of the Z is not a "room" and the heat would be blowing down towards the floor.

To determine if in fact you have a 73 vs a 70/71/72 look at the back. If you have three light bulb holders behind the lever control area, and the face of the HCP is smooth, it's a 73. If on the other hand, there are no lights and the labels for the levers are above the lever on "tape", then it's an earlier model.

You can pretty much use them interchangeably. To use the 73 on an earlier car, you'll have to splice in the light wiring hanress into the light circuit (BLUE / RED STRIPE wire) and make sure that you can slip it into the dash without problems.

When I put a 73 HCP on my car (a 71) I found that I had to mount the HCP first and then the center console. The FSM and most other books will tell you to do the center console first and finally the HCP.

Hope this helps.

Enrique