On our Light A/C we have placed a blanking plate to stop the direct ram air cooling flow which is under the engine baffles. This normally keeps the oil temps down by flowing around the crankcase lower and the oil tank (Continental C-85). . .In the winter if you don't block off this air, the oil temp does not reach an acceptable level...(to boil off any condensate within the oil)
On A/C with oil coolers fitted it could be a plate fitted directly to restrict air flow to the cooler.