AC Clutch wont engage
April 1st, 2019, 4:36 PM
#1
AC Clutch wont engage
Hello. My name is John. I have 50 years in the auto repair and accessory trade. I recently purchased a 2005 2500HD .I realize the clutch wont engage with a low freon charge.Should the compressor relay close with a low charge or does the pressure switch regulate the negative to close the relay as well as the negative to the clutch?
April 1st, 2019, 6:12 PM
#2
the compressor clutch relay is controlled by the pcm. the pcm supplies grd to the control side of the relay...this closes the relay to provide power to the compressor clutch.
the low pressure switch is an input to the hvac control module. if the hvac module does not see a closed switch ie. low voltage on the pressure sense wire....it knows the pressure is low. the hvac module sends pressure switch information to the pcm. the pcm then will not start the relay until it get a closed pressure switch info from the hvac module.
if you BRIEFLY jumper the pressure switch connector and the compressor engages...either the switch is bad or the pressure is low.
the low pressure switch is an input to the hvac control module. if the hvac module does not see a closed switch ie. low voltage on the pressure sense wire....it knows the pressure is low. the hvac module sends pressure switch information to the pcm. the pcm then will not start the relay until it get a closed pressure switch info from the hvac module.
if you BRIEFLY jumper the pressure switch connector and the compressor engages...either the switch is bad or the pressure is low.