High Temperature Service - For Controllers

I would be much more worried how hot my motors and drive electronics would be in these temperatures than the controller.

To answer your question requires a lot more detail but my initial preference would be to use a harsh environment PLC. No sparks from contacts in a hot environment and flexibility in a loose design.

I would use the same modern, reliable control gear and just keep the control cabinet cool with air conditioning, vortex cooler, intelligent design (sun shades, insulation, etc), etc if I couldn't keep the control room itself cool using the same methods.

Fix the source of the problem and all that jazz.

58 degree temperatures are not that high, and although it will degrade controllers containing capacitors if a cooling solution is not economically viable then locating the controller in a cooler place or just plain reducing its end of life and replacing often is really the only option if you want anything more than contactor-based control.

the site is actually inside the milk processing environment. Aircondition is not advisable-foremost moisture on the vicinity as this would inhibit microbes that might contaminate the product.