Engine Size: 7.2L
Ambient Temp: Any
After I have been running the A/C for 20 mins or so the air starts to just barely blow out of the vents. The sound kinda changes too. It sounds louder and like it is blowing around inside the dash. I don't know what the problem is, any ideas?
Either the evaporator core is freezing condensed water around it (blocking air flow) or a diverter door/flap is sending the air elsewhere (feel under dash, at windshield defroster vents, etc). If ice on evaporator core, can be caused by low charge of refrigerant.
Pop the hood next time- see if a/c lines are frosty white.....or just shut it off and see if you gets massive amounts of water (melted ice) under the truck. If so- freeze-up is your issue- most likely from a faulty cycling switch.
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......
I had to live with that for awhile until I got around to repairing it, first sign is a musty odor from the vents. At that time, switch off the compressor with the blower running at full speed. When the air started to feel warm, switch it back on again. Not sure if you have the economy mode or a compressor switch, but the same difference. If this works for you, does verify the problem.
Not sure if you have a variable displacement compressor with control valve problems or the cycling switch, would have to open the hood to determine that. It's less of a problem when it is really hot outside.
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