If you're talking about cockpit/cabin pressurization, there is no difference in the differential pressure (the difference between cabin pressure and ambient atmospheric pressure) between pax and freighter aircraft.
However freighter crews often seem to adjust the cabin pressurization rate of change
to the high side. Meaning the cabin pressurizes and depressurizes quicker. Nominally, when aircraft climb, the cabin pressure decreases 500 feet per minute and during descent, the pressure rises approx. 300 feet per minute. Often on the DC10, the rate knob is turned a bit above normal.
If an aircraft is designed to have heated lower cargo compartments, so will the cargo version. If a compartment cannot be heated due to malfunction and is MEL'd, you cannot transport certain types of freight and will take financial hit.
Fedex carries a lot of race horses along with their handlers and they maintain the main cargo compartment cool for the sake of the horses (or so I overhear the handlers say).
The air conditioning system besides controlling cabin temp and providing ventilation also has the critical role of pressurizing the airplane.
On pax airliners, they operate all the air conditioning packs (unless one was inop of course). But on cargo aircraft, they will use only one or two to save fuel when possible. Now you might think then that cargo aircraft don't pressurize as much as pax planes. But that's not the case, it will pressurize fine but with less ventilation due to less air inflow into the cabin. But don't forget, you've only a handful of people in the aircraft versus potentially hundreds, so as long as satisfactory pressurization is maintained air quality should be OK.
Interestly, the MD11 pneumatic/air conditioning system is fully automatic and runs all three packs when the system is in auto.
Another interesting thing is most of our DC10's are certified to operate only 2 out of 3 packs in flight. A long time ago I researched why and found the answer in the flight manual. Reason being is the smoke detection system on cargo DC10's are certified with only 2 packs on.
Find the fuel totalizer that reads 26600 lbs then go straight up to the cabin pressure panel. Notice the rate limit knob white arrow is aligned with the white "pip" mark. On cargo "10's", it's usually cranked to the increase side for faster pressurization rates.
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Photo © Peter Brooks
You're only as good as your last departure.