Without that fan running you’ll get heat-creep which will eventually result in a filament jam.
The extruder has a “hot” and “cold” end … separated by a gap they call the “heat break”. The design is to allow the hot end to get hot… but the gap prevents heat from easily transferring to the cold side. The heat-sink and fan on the cold side deal with any heat that does manage to creep across the heat-break gap. But if the fan isn’t running, heat will migrate and eventually heat the cold end to the point that it is hot enough to pre-melt filament and result in a jam.
Check to make sure the wires have not come loose on the board.
Unplug the printer from power. Open the left side-panel of the printer, you can access the board.
Along the top, you’ll see the heavy wires that run the power to the hot-ends. The Workhorse is “wired” to run two hot-ends even though it only has one (if you look at the back of your printer control box … next to the USB port … you’ll see the plug to connect the wire for a 2nd hot-end). Those plugs along the top run the hot-end heat and also the blower-fans (part cooling fans). Those are not the fans that cool the cold-end of the extruder.
To the left of that row, you’ll see (circled in the image I uploaded) two pins… those provide continuous power and that’s where the heat-sink fan is connected. The board is labeled “5V AUX OUT” (it’s a 5v fan).
It may have become disconnected (I’ve noticed it’s not a particularly firm connection). Make sure that’s plugged in.
Reconnect power to the printer and switch it on. After it boots to the main status screen the cold-end fan should immediately switch on and stay on. It is normally always powered as long as the printer is on.
Since it’s just a simple 5v two-wire connection, it should be pretty easy to make sure power is connected. If necessary… you could use a multi-meter to test continuity to make sure there isn’t a break in the wiring.
Stay health & safe.
Tim