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AC Control I just purchased a used C2500 and noticed that the AC control does not work on Low or Medium. It does work on Medium and High. Do you have any solutions? Thank you! Charles
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Could be a number of thing's ! Testing the electrical circuit is the way to find out what's wrong . Using a wiring diagram and a DVOM - digital volt ohm meter . Videos on youtube showing how to test it ! Without testing i would only be guessing . Does it work in high speed ? In high speed it by-passes the resistor . If it doesn't work in any speed more then likely the blower motor is the problem !
Air Speed
The HVAC control assembly applies ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:
• Low speed--3 resistors
• Medium 1 speed--2 resistors
• Medium 2 speed--1 resistor
When the operator requests High speed, the HVAC control assembly applies ground directly to the blower motor through the high blower motor control circuit. The resistor card has a fusible link which, if blown, will require that the card be replaced.
AC switches only turn on the compressor clutch. The switch you are referring to controls the blower motor in the cabin and is controlled through 3 resistors that vary the speed . IF it only works on high then the low and medium resistors have burnt out.
If you blower fan will only work on high know that most blower motors are power by a basic electrical circuit that utilizes a multi resistor or a solid-state resistor to control different fan speed modes (low, medium low, medium and high). If the resistor malfunctions it may lose one or more of the lower fan speed settings. First check the fuse and change if needed. If that doesn't fix things change the resister.------------------------------------------------------------------------------------ Launch CResetter Oil Lamp Reset Tool
On any other vehicle it sounds like the blower fan switch. The fan switch provides power or ground to the resistor and there would be a high speed blower relay to bypass the resistor. But in your case the fan switch is part of the controller. I don't have a diagram for a 92 but the 94 model shows relays for low medium and high speeds. Each relay gets power from a fuseable link. The high relay gets power thru the low relay if the low relay is not engaged. If you have the model with 3 relays you may need to check them.
You replaced the resistor and WHAT relay? The blower motor circuit on a 2007 Dodge Nitro does not use a relay.
The blower resistor gets it's power from the A/C - heater control unit.
If you check for voltage at the blower motor resistor connector (Key on, relay disconnected), the DARK BLUE/GREY wire should be hot when the control switch is on HIGH. The DARK BLUE/VIOLET wire should be hot with the switch in the MEDIUM 2 position.The DARK BLUE/ORANGE wire should be hot with the switch in the MEDIUM 1 position. The DARK BLUE/BROWN wire should be hot with the switch on LOW.
If any of these are not as stated above, then you either have a bad A/C - heater control unit, or faulty wiring between the control unit and the resistor.
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