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Chevy s10 a/c

i have a 98 chevy s10, 4cyl, 5 spd, 111000 miles, the compressor does not always engage when i start the motor, sometimes it does and sometimes not. if i turn the ignition off and restart, the compressor comes on. when it is on, it blows very cold air

First thing I would check is what voltage is present at the compressor clutch coil connector. You stand outside the truck with a multimeter hooked up and a friend works the switch. It could be a voltage problem or it could be the air gap in the clutch is to large,maybe even dirty.

thanks for your suggestion. i checked the voltage and the air gap, but to no evail. still have problem.

The old intermittent problem problem. It could be lose or dirty connections on the electric plug to the clutch. It could be something in the HVAC controls or ignition switch( try wiggling the ignition when it happens).
If you’ve checked the temp. from the vents and it’s really making good cold air it has to be electrical. Does the clutch engage crisply when it does actuate, with no slip and every time, it could be the clutch but doesn’t seem likely.

when the compressor comes on, it comes on cleanly and crisp. the last two days it has been coming on each time i start up. i will try the ignition wiggle and will check the electric plug again. thanks