I have a 71 Chevelle that was an A/C car and I converted it to heat and defrost. My question is what is the part that I need to control the speed of the fan with the switch on the control panel? I am looking at the OPG catalog and it has a blower motor resistor assembly but it is only list to 67-70. Then right below that is the Blower motor relay and it is listed for 69-72. Which do I need? They are listed on page 459 of the OPG catalog. Thanks for any help in advance.

You need the resistor unit. I don't have an OPG catalog so I don't know if the resistor unit is correct for A/C, the heat only resistor unit is not the same as the A/C resistor unit.
For resistor cooling the unit needs to be installed so that the blower air flows across the coils .

If you want high speed then the relay is also needed. When using heat only on your car you don't need high speed.

Did you remove the evap box? The resistor unit and relay would have been on it.

Well when I got the car it still had the A/C box inside the car. When I took it off I did not see a resistor. Does anybody know were I could get this part, picture of it, or even have a part number for it? Would it be possbile to make something up with relays and so on that would work the same way?

This (http://imagehost.auctionwatch.com/bin/imageserver.x/00000000/azss/68fnspdres.jpg) is very similar to the resistor unit you need. It's a 68, it has three connections the 69+ has four. If your evap box had one it would be installed in the same location as the one pictured. If you don't have one post a want ad. It should be easy to get a good used unit.

Thanks for the help and the picture.

When you converted to heat and defrost, how did you do it? The A/C cars have this resistor outside in the A/C firewall box. Non-A/C cars have it inside. In fact, most likely you have two sets of wiring in your dash, one for the A/C and one that is heater only. There's probably a connector on the non-A/C harness that'll help you get the right resistor. Now, where to install it? Did you replace the inside heater box? If you left the A/C interior box in place then there's no place for this resistor...

This is what I did to convert to heat and defrost.
I took all the A/C stuff off and welded the hole shut. Found measurements for the hole that would need to be cut out to convert to heater only. Then bought the heater box for the outside and the inside. I did not use the original wiring harness. I decided to go with Ron Francis Wire Works kit. I didn't realize that the kit that I got did not have the wiring for the blower motor. I checked out there site and it looks like they have a heater wiring kit but I am not sure if that will work. I just sent them a email and should hear back some time later today.

Sure wish you had provided that information at the beginning. Disregard all of the information I posted previously. Your resistors are inside on the heater box, no relay needed. If you don't get what you need from Wire Works, I can provide the needed wiring. e-mail if interested.