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Reply to "Air conditioning piping runs"

On our '72 L, the evaporator valve under the dash had a 'final filter' in the side arm going to the evaporator core. It was a small (1/4" OD) filter of fine copper screen rolled into a 1/2" long cone. The screen appears hand made. It was completely blocked by tiny pieces of rubber from the hoses, bits of disintegrated dryer pellets, reddish flakes and who knows what else. Hooked it out with a scribe and soaked it in paint thinner for a while, then flushed with solvent & returned it to duty.

Because r-134a is a poorer AC fluid than R-12, higher flow is reportedly needed to get adequate cooling, so shops remove the screen if its there. An evaporator valve suitable for r-134a supposedly uses a different calibration spring inside that valve. If you want, the screen will fit (loosely) in any valve. I once cut apart a 40-yr old  OEM dryer can and it appeared to be 1/3 full of concrete/oil sludge like you'd find in an old neglected engine's crankcase. No trace of 'dryer pellets' as such. This is why the screen was in the OEM system, I guess.

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