AC Switch - only full setting works

[GT2BH]

My AC doesn't turn on unless I use the maximum setting. The first 2 don't do anything. Is this a switch problem or do I need to look at something else?

[T77911S]

when a fan only works on HI, that usually means the resistor network for the lower speeds is bad.

[tkmoore]

There is a large Resistor behind the passenger side footboard called the evaporator blower resistor that is usually the culprit of the problem you describe.

[kuehl]

It could be either the AC Fan Speed Switch or the Evaporator Fan (speed)Resistor pack.

Referring to the circuit below (found on PP).
You can test at either the fan speed switch or at the resistor pack.
I'd suggest testing both. In some cases you can repair the resistor pack contacts, however
the switch cannot be economically repaired; we suggest replacing the switch since they tend to old and carry a lot of amps, and replace the primary AC relay in the smuggler's box well, replace it with a relay with a value of 20 amps minimum (original factory value back in the day, avoid the current 15 amp units, this is a common relay.

Open up the center console to access either the back of the AC Fan Speed Switch or plug attached to the back. Be careful when working in the center console, not to damage the thermostat's sensor tube (an aluminum tube typically covered in white plastic sheath); if you bend or break the aluminum sensor tube you will need a new thermostat.

Remove pass'g side, RH foot board on LH drive models. The resistor pack is inside the plastic trapezoid vent inlet leading to the evaporator box. If you can't easily check the test points where the wire harness plug from the fan speed switch connects to the resistor pack then remove the 4 screws holding the plastic trapezoid into the bulkhead and remove the assembly.

There were 2 versions of design for the resistor pack, both have the same circuit.



Referring to the schematic, With ignition key on clockwise to accessory position, using either a test light or VOM:

1st 'on' position switch, low speed
Power should be at 'L" terminal on back of switch or in the mating plug, Red wire with green stripe, and power should be at position '3' at the fan resistor pack

2nd 'on' position switch, medium speed
Power should be at 'M" terminal on back of switch or in the mating plug, Red wire with black stripe, and power should be at position '4' at the fan resistor pack

3rd 'on' position switch, full speed
Power should be at 'H" terminal on back of switch or in the mating plug, Red wire with white stripe, and power should be at position '4' at the fan resistor pack

If you find your circuit issue at the resistor pack then read this link:
Karl's AC Journey



If you decide its time to upgrade to something better then review this product:
Kuehl Evaporator Fan Variable Speed Controller
and PP sells it here under part number GR-KUEHLSPEED


PP sells the OEM style fan speed switch here under pn 911-613-243-00-M100

[wwest]

30A PWM fan control, just a bit less expensive vs Kuehl.

Multiple sources on EBAY, one of these quite possibly the same as Kuehl uses.

Also, you can add a switch to alternately control the cabin heat blower/fan.

"Finer" modulation of cabin heat level that way.