How do I replace an infinite switch on a frigidaire professional series range? Model PLES389C.

SOURCE: pf code on frigidaire professional series free standing range

"PF" indicates the electronic control detected a Power Failure.
This could have been caused a brief power outage OR may be an indication that the connections to the oven, either at the stove or at the plug are loose.

SOURCE: Where is the fuse panel

I can help , The fuse panel/control board is located behind the digital display in the front of the unit. Some drop in ranges are tricky getting into so be carefull when removing the face , there are screws under the display when opening the oven door look up and there may be a few more on the top side corners reveled when you pull the unit out 12" or so. there is a small glass fuse in the board some of these are not removable so if there is no digital display on your oven and your sure you have 240V to control board you will need to replace the entire control board. Hope this gets you there. Good luck let me know if you have anymore problems.
Phil

SOURCE: My Kenmore glass top range,

SOUNDS LIKE YOU MAY HAVE A WIRE BURNED. CAN YOU USE A MUTIMETER?

SOURCE: instruction manual for a frigidaire professional series PL36PC40E

frigidaire.com/manuals

SOURCE: F30 ERR message on Frigidaire Professional Series Range

I am a tech and just had this happen to me, so I can feel your frustration. I have replaced the temp probe, erc, and still had the problem.
Open the back, with the unit unplugged. On the lower right hand side there is a relay, beside the relay there is a "safety T-stat" disconnect from the circuit by removing one wire and read for continuity. If none is detected, replace t-stat and voila... stove works. Much cheaper than erc and probe...