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Disable Automatic AC When Defrosting

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For 1994-1997 Rams with the 7 position fan switch     [1998+ below]

Some of us didn't like the way the Ram always runs the Air Conditioner when the HVAC control is in one of the defrost positions. With the diesel especially, engine heat takes a long time to appear and the AC didn't help the windshield warm-up time. With the AC running, frost and ice on the OUTSIDE of the windshield is difficult to melt until the engine reaches operating temperature. With this modification, the AC compressor only runs when the fan switch is turned to the AC position.

From: "Roger L. Story, Jr." <rtea1234<at>>
From: (Hammaker, Jeffrey)

The first step, is to remove the cup holder and ash tray. Extend them to the working position, and use a Phillips screwdriver to remove the two captive screws on each item. Then using a flathead screwdriver, pop the dash cover from the rest of the dash. * Hint: It helps to put on the parking brake, put the truck into 1 low, and move the tilt steering to the lowest position.

Now remove the four screws holding the climate control to the dash.

Turn the temperature control knob to the coldest position, push in on the red cable lock that holds the damper control cable in place, tip the cable up and remove the cable from the sliding gear. Pull off the temperature control and the mode selector knobs.

Disconnect the electrical plug and the vacuum distribution manifold from the rear of the unit.

Remove the unit and notice the black tamper-proof screw on the back of  the unit. We filed the center of the screw down until the Torx size T10 driver could get a grip on the screw. Remove this screw, then use a screwdriver to pop the four plastic retainer tabs from the four corners of the rear of the unit and remove the rear cover. Take caution at this point, as we broke one of our tabs off.

See the black wafer that corresponds to the mode selector knob, take it out, notice the two contacts grouped together. We'll, pry out the outer contact and its spring. If you remove the inner contact, the fan will not work at all. Then reassemble the unit, reinstall it and put the dash back together. No more ac on defrost

I added:
Photo by Ryan - AKA on the TDR  as "Cooker" The contact is a small piece of copper with a spring behind it. I don't remember which contact it was (and it may depend on the model year), but it was fairly easy to figure out. One contact (for the fan) had a wiper that extended into all positions, and the contact that you need to remove (for the AC) has a short wiper in the two defrost positions.

To remove the T-10 Torx security screws, I took a needle nose plier and bent the security pin from side to side until it broke. Then a standard T-10 bit easily removed the screws. The local hardware now sells Torx security bits, so you may be able to find one locally.

The whole operation took less than an hour. After the mod, the AC only runs when the fan switch is turned to the AC side for any position of the mode switch position.

For 1998-2001 Rams with the 4 position fan switch

The fan switch does not have a position for AC, so a separate switch must be added to the HVAC control to disable the AC compressor.

If the HVAC control is disassembled and the defrost contact is removed, the AC will be permanently disabled. The only option for a selectable AC disable switch is:

When the weather cooperates and I get some time, I'll dive into Sue's 2001 and see what is actually involved. In the meantime, see Making a Manual Switch for the A/C on the TDRoundtable for instructions and photos of how the switch assembly can be modified to accept a Toyota AC on/off switch.


Page last updated: October 6, 2006