a/c cutting off at high heat loads and engine tends to heat up slightly.
Is there a test for the fan clutch? on 1993 Ford F-150
How does it do on the open road running 55mph, or so?
That's when it cuts out. works great otherwise.
Does it heat up in traffic, in town driving, or out on the open road running 55mph? The fan is not needed with all that RAM air at 55mph! Just when running slower and at idle. 1993, replace the fan clutch, and look closley at the raidator!
is there a test for proper operation of the fan clutch?
Not really, start the engine, let it idle until hot, the fan should be working it's hardest at this time. If it dosen't pick up speed and you hear it roar a bit then replace it. You just have to know what to look for. Also try to move it back and forth to see if clutch has excessive play. Should have some resistance when turning by hand, again you just have to know what to look for! Can't show you, unfortunately.
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get engine warm, turn a/c on. at idle, fan should be turning pretty fast and should feel air above engine being pulled through radiator. if slow or not much air felt, probably fan clutch.