I have a 76 & 77 BJ40 here in Costa Rica, one w/ an HAC. The 76 is my current daily driver and does well w/o HAC. I live @ 4650 ft and my shop is located @ 3300 ft. The 76 has no issues climbing the mountain back home. My question: what is the purpose of the HAC? 77 is close to completion and will be exported to CA as my vehicle, NFS. We'll build to order but the project 77 is being built as a collector as are all my builds but this is my first Toyota. Any information about the HAC purpose and or function would be appreciated. Thanks.