My home has split AC. One is American Standard Mod # ATNO 36C100B0 - manu. 12/92. The other is a Rheem Mod # RAFD-031 JAS - manu. 12/89. I live in S. Florida. Can someone tell me the SEER value of these units, and your opinion as to replacing them with 12 SEER rated units. My elec bills run $300-$400 in the summer months.