PWM is Pulse-width modulation
Fan is 12v and PWM changes pulse to control the fan speed. The slower the pulse is slower the speed.
We need to find a an exhaust fan that moves same or more air than cooler fan. The reason we want the exhaust fan to pull as much or more air out of case than the heated air cooler coming out of cooler.
Problem is the coolers have 140mm fans and your exhaust vent is only 120mm

120mm fans move about 2/3 as much air than 140mm fans. That is why I have been slow in saying what fan I think you should get.
BeQuiet! moves 50cfm but Thermalright TY-140 moves 73cfm.... so 23cfm of heated air from cooler would not be removed from case.
What I'm trying to find is a 120mm exhaust fan that will move up to 73 cfm and not be too loud. Even Scythe Gentle Typhoon 1850 only moves 57cfm. Scythe Ultra Kaza 3000 moves 78cfm but is 45dBA... quite loud. TY-140 is 21dBA & every 10dBA increase doubles how loud something sounds to us.. 20dba to 30dBA is twice as loud to 40dBA is twice as loud again so UK3000 is 4 times as loud

They claim 40-50dBA is similar to library or home normal volume level but 45dBA is probably about what you stock cooler sounds like.
Only other way I can think of would be to build a duct/tube from cooler to back exhaust vent, but that might block the PSU intake.