Air compressor unloads too quick

Have a 2013 Maxxforce 11. Only when cold and after air builds and purges, air pressure drops 5-10 psi on secondary tank after a minute or so and the compressor starts building again. Once coolant is above 170 all is normal. Replaced governor with a spare I had with no change. Thinking unloader problem but have found conflicting info on Bendix site as to where the unloader is. Is it on the top of the compressor or a separate component? Read about a service kit also. Thanks for any help.