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RR/HVAC fuse 30amp located in the under hood fuse box. You can check it but highly doubt it's the problem . More then like it's the blower motor control module that's bad .
The auxiliary blower motor is a variable speed fan. The HVAC control module controls the fan speed by sending a pulse width modulated signal to the auxiliary blower motor control module. The auxiliary blower motor control module varies the duty cycle across the auxiliary blower motor in relation to the pulse width modulated signal. The auxiliary blower motor speed can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is high speed fan.
Watch this video for testing purpose's only , this is a front blower motor control module . Same way your back one works . GM is GM Chevy , Buick ,GMC , Cadillac .
I WOULD HAVE TO SAY, NOT EASY. ORIFICE TUBE IS LOCATED ON THE REAR QUARTER PANEL INSIDE OF SUBURBAN. THE FREON NEEDS TO BE CAPTURED BY A FREON RECYCLING MACHINE. THEN THERE ARE SOME PANELS THAT NEED TO BE REMOVED TO GAIN ACCESS TO THE H.V.A.C. BOX , THIS IS WHERE YOUR HEATER CORE, EVAPORATOR CORE AND FAN BLOWER ARE HOUSED,THE SMALLER METAL FREON CONTAINS THE ORIFICE TUBE THAT NEED TO BE PULLED OUT. I WOULD STRONGLY SUGGEST TO YOU TO HAVE THE FREON PRESSURES CHECK FIRST, CAUSE WHEN THE FREON IS LOW THE REAR A./C WILL NOT WORK AS GOOD ANYMORE. PRESSURE READING SHOULD BE: LOW SIDE 35-45 P.S.I. AND ON THE HIGH PRESSURE SIDE IT SHOULD READ: 200 - 250 P.S.I.ANYTHING DIFFERENT IF BOTH PRESSURES ARE LOW, JUST ADD SOME FREON VERY SLOWLY UNTIL PRESSURES ARE WITH-IN THOSE RANGES.
I'm going to assume manual but Auto is simular and i can give some direction if you have that as well.
There will be a black with tan wire at the blower resistor. This is the wire the HVAC control head grounds to turn the fan on high speed. With a test light hooked to power unplug the resistor, set the blower speed to high, turn the key to the run position. the test light should turn on when you probe the connector. If it doesn't pull the control head and back probe that same wire at the back of the control head with everything still plugged in. If the test light again does not illuminate the the control head is bad and not providing ground
If the test light does turn on when you probe the blower resistor connector plug the resistor back in. Turn the blower speed to the low setting. With your test light hooked to ground see if there is power on the black with tan wire. if there is turn the HVAC off and ground that wire with a jumper wire. the fan should run at high speed. If it doesn't you have a defective resistor.
most of the time the resistor is located downwind of the blower motor so it should be not to fao from the blower motor in the right rear of the van behind the quater trim panel which is the hvac unit is located
I went through the same thing with my 99 suburban. It turned out to be the dash fan control switch. It is purchased seperate from the whole cluster for under twenty dollars. The instrument panel cover comes off gently by hand with the tilt steering in the down position. You have to then unplug the electrical plugs to get it out of the way. The heater ac control panel then comes out by hand far enough to unsrew the heater fan control from the back.