Maintenance on package unit. Checked static pressure, refrigerant pressures, temperature differential, amp draws on compressor, fan and blower, condition of coil and blower assembly, ensure drain line was clear and flowing. Found unit with a very high static pressure. Also, it seemed that the return had very little suction. Found that the return duct coming immediately off the unit was collapsed and is sucking in air from the crawlspace. Will need to repair this duct.