I had 2 9220's, both had same issue.  The control valve on the dash for temp.  was letting in hot
when all you want is cold.  The solution was to put in a shutoff valve in the heater hose under the cab,
left rear.  Easy to access, did it with both tractors.  Just get one of those simple shutoffs like
we used in the old days, cut the hose and put in the needle valve.  Any auto parts store will have one. 
In spring or late fall, when you need heat, open it back up.
Let us know how it goes.