https://www.ipdusa.com/products/6615/Air-Conditioning-Bypass-Kit-240-1978-1984-for-Volvo-IPD-106153

If yours is the later style and doesn't have a bolt-on P/S pulley, but rather a press-on P/S pulley then you need this kit
https://www.ipdusa.com/products/20924/Air-Conditioning-Delete-Bracket-Kit-240-B21-B23-for-Volvo-IPD-139672.

Surprisingly, both are still available. Subtract off the price of the belt to get a better idea of what you're paying for the parts. If you search around hard enough, some people came up with homegrown versions of the later bypass kit.

Having said all that, as long as the A/C compressor clutch turns freely and the A/C is not activated then keeping the A/C belt and driving only the A/C pulley and outer clutch places minimal extra load on the engine during running to affect overall fuel mileage. During acceleration there is a little extra load for the momentum needed to get the clutch and pulley up to speed, but nowhere near as much as if the compressor was engaged.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now