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New to the group so if this is posted somewhere else please point me to it

I have a 98 gmc serra c1500. The blower was making an awful sound and a bit later the blower would only run on high. Fast forward a few years of not having ac or heat.

Decided to fix it...finally. so replaced the blower motor and resistor. Great. Now all the speeds work and the blower is blowing. But nothing is really coming through the vents.

Take the blower back out and clean the coil (realize now I should have done this when replacing the blower but live and learn). Check (best I can without moving the dash) the actuators and the fin move but it seemed one fell. Took that out and now the air blows better but not cold.

Check the compressor and it is not engaging. Great (sarcastically). But checked to see if it really was not working so I checked the compression switch, looked ok but unplugged the wire, used a paperclip to short it and the compressor engaged! Yea, means a bag compression switch. Easy.

Today, new compression switch and....nothing. no change. I don't know what to do next. I don't know gauges, and pressures, how to find leaks etc.

Any help would be amazing!
 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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Today, new compression switch and....nothing. no change. I don't know what to do next. I don't know gauges, and pressures, how to find leaks etc.
That's your low pressure cycling switch telling you you're low on refrigerant (Freon). You need to put a gauge on it to confirm.
 

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Sorry, typo. "Bad compression switch". (top) located on the passenger side, evaporator.
you have to use the ac pressure gauges ... pressure is 80F air temp and the Freon is 110PSI.... then the pressure is below 20-25 psi low port then add the R134 Freon ..compressor does not run 20-25psi.. or on/off ...
if the freon is a leak then use the UV oil in the ac pipes ... then inspect the UV leak its a yellow color ..
the freon is around 28 OZ then add an oil 2 OZ refrigerant ..
look up the ac compressor probably has leaks on the oil of the compressor ..
my 1996 Impala had compressor leaks replaced it ..
 

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Compressor will not engage if the system is too low on freon. Buy a can of Freon with oil with a hose and gauge attached at Walmart. Connect it to the low side quick connect, it’s the only connection it will make. The high side is different. Start truck and turn on AC. check the gauge for pressure, if none then system is empty and probably has a leak. If you have a little pressure then add Freon and watch the compressor. Once the compressor engages stop giving it freon and look at the pressure. the goal is to get the pressure in the green while the compressor clutch is engaged, After you get enough freon in the system so the compressor will engage then ADD FREON ONLY when the compressor is engaged, STOP WHEN THE COMPRESSOR STOPS, ADD WHEN THE COMPRESSOR IS ON until it keeps running THEN STOP and check the gauge, add Freon until the gauge reads about halfway or less in the green. DON’T TRY TO FILL IT TO THE TOP OF THE GREEN.
NOTE: when the COMPRESSOR ISN’T ENGAGED the pressure reading will be much higher 60-100 psi. this is normal.
 
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