Were you referring to the PW water cooler, TIG225, or one of their other welders?
I bought the parts for my TIG225 but haven't swapped yet. It uses 2 standard 120mm fans and they plug into one of the PCBs. I debated getting a PWM temp controller, but quality fans should be pretty quiet. Like
@Weldo pointed out: you do want to make sure you get a fan which is designed to work on a radiator/heatsink (not a case fan). The TIG225 fans are right up against some big heat sinks and one of them is also ducted. I'm designing a duct adapter for the new fans because they are about 1/2" thinner than the original fans. If you're interested I can dig up the part #'s for the plugs/pins/fans and share the duct once I make it.
I had opened up the water cooler when i first got it and its nearly identical to the HTP and Everlast, so what Weldo did should work for these models too.