I should have been a bit more specific when I asked about effeciency of the R4 vs. a ND compressor. I turn on the ac its like goodbye turbo. The compressor eats up power. Same results on both 300D's.

Does a ND compressor require any less HP to rotate than an R4?

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)