The retired engineers that I have talked to, all said that the F units or "covered wagons" were a real pain with which to switch. Especially when trying to look backwards from the cab. Mike Porter here in Kansas City who worked on the Chicago, Great Western (CGW), Chicago And North Western (CNW) and Union Pacific (UP) was especially vocal in his dislike of using this type of unit for switching moves. The control stand was a really uncomfortable stretch from leaning out the side window to look back to see brakemen signaling moves.
Of course, as they say: Never say "never". If you have the Morning Sun book Frisco in Color Volume 2 take a look at the picture seen at the bottom of page 14. It did happen, and in that case even with an FA-1m. Edit: Forgot to mention that a retired KCS friend of mine mentioned that he knows of one time a single F unit was dispatched to handle the AW Branch, Heavener, OK to Waldron, AR. There were no turning facilities, so it had to run in the backing position with its train on the return trip with a brakeman riding in the doorway to stop and flag the crossings.
Yes sir, never, ever, say never. It might have not been the best, or the most favored unit for service, but it was the one ready for the service. As most EMDs of the time were, it was always ready. That unit with a ready and able crew, were the ones that got it done.
Not Frisco, so maybe off-topic, but the Missouri Pacific used to sometimes run a single F-something 50 miles down the former New Iberia and Northern from the NOT&M mainline at Port Barre to New Iberia. I would see it parked next to the engine house. Never saw it moving, though. Of course, being 15 at the time, I did not have the sense to ask anyone anything about it. How do you do back up switching moves and things like that? There were wyes at both Port Barre and New Iberia so it obviously got turned on either end. Every time I saw it by the engine house it was pointed north, outbound. There was a nightly round-trip run from New Iberia to Port Barre and back. So it is very conceivable that the F unit only pulled the train each way and did no switching. Although, at Port Barre, loads from the salt mine down by New Iberia had to be set out, and empties picked up, so some certain amount of switching had to be done. At 11:30 at night in the dark. Heading further south and east out of new Iberia were two subordinate MP basically spur lines. One going 35 miles to the east, serving a couple of sugar mills, and the other going about 8 miles south to serve a salt mine The salt mine was the major customer of the entire branch, sometimes 100 carloads a day. You might have heard of that mine, it is the one that got drilled into by an oil rig barge in a lake above it back in 1980. It flooded the mine and killed the whole MP operation entirely. There were no turning facilities at the end of either one of these short lines, so I doubt if they ever ran that F-unit on either one of them going even further out away from the mainline. Those two lines had their own locomotives anyway, New Iberia always had 3 engines total on hand. Sorry to diverge, but it seemed relevant, first hand account of a single F-unit running on a branch.
The MoPac regularly used an F7A solo on its branch line from Thebes, Illinois to Cairo. I have tried in vain to find it, but I have seen a photograph of an F unit sitting beside the MP freight house in Cairo. This is where I used to play on the freight platform when I was very young. Ken McElreath