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94 Toyota 4 RNR on and off AC

Safe Crackin Sammy on Sun September 20, 2009 10:43 AM User is offline

Year: 1994
Make: Toyota
Model: SR5
Engine Size: 3.0
Refrigerant Type: R134
Pressure Low: 24
Country of Origin: United States

Looks like a great site for info!

Let me start by saying I am not an AC tech but a decent mechanic.

Wifes 1994 Toyota 4 RNR 3.0 SR5 has always had good ac til last week...

Tested it yesterday and heres what I found....

When parked and cool, ac works fine [40 degree output temp] from engine start til about 4-5 minutes of run time at idle.
[air temps here in the 70's]

Low side pressure runs around 24 pounds..

Then I hear the compressor kick off and the low side pressure goes to 65-70 pounds and of course luke warm air and a funky stale smell from the vents.

Any suggestions as to the problem or the cure?


mk378 on Sun September 20, 2009 11:36 AM User is offline

Wait until it quits and the air gets warm. Use a hammer handle or similar tool to tap on the clutch plate and see if it snaps in and starts cooling again. If it does, the gap is too wide-- take some of the shim washers out.

NickD on Sun September 20, 2009 8:20 PM User is offline

Sounds like your compressor is kicking out, but why? Could be excessive gap between the idler pulley and the clutch hub, like about 20 mils, 30 mils is max, can remove the clutch hub and remove a shim or two to close it up, they do wear out increasing the gap. Also could be your dual function switch is kicking up, but you don't list high pressures, due to a plugged condenser or an inoperative radiator fan. Stale air indicates your evaporator is moldy, that needs cleaning. You can watch your clutch hub kick out under your conditions, question is why. Also a thermo switch in the evaporator can be defective, another sign of stale air is the evaporator is freezing uo.

Safe Crackin Sammy on Mon September 21, 2009 7:50 AM User is offline


I wont get a chance to work on it for a week or so but I'll check it out and post back.

Thanks for the info!


Safe Crackin Sammy on Sun September 27, 2009 8:57 PM User is offline

Got a chance to run some more test on this today and here is what I found..

Low side 30 at idle to 45 pounds at 1500 rpm.

High side 200 at idle to 350 pounds at 1500 rpm

40-45 degree cold air at vents

After three-four minutes compressor clutch kicks off and condenser fan also stops... Low goes up to 90 and high drops to 125 slowly.
Clutch wont restart til 5-10 minutes of cool down time. During this time I can run the clutch with a hot lead from the battery.
So I assume the compressor and clutch are good.

The shorter the cool down time the less the compressor will run next time til it kicks out again.

There is normal condensation drip from the evap under the car.

Whats making the clutch kick off like this?


mk378 on Sun September 27, 2009 11:14 PM User is offline

Seems to be cycling off normally on evaporator temperature, but not restarting for some reason. It should restart before the air gets warm. The condenser fan doesn't restart either, indicating the system doesn't want to engage the compressor at all. It may have a simple thermal switch, or there could be a computer or "amplifier" involved. You'll need to get the schematic of the truck and trace through the control system.

bohica2xo on Mon September 28, 2009 3:28 AM User is offline

Are both condensor fan speeds operational? The fan should go to high speed about 220 psi on the high side.

The amplifier is inhibiting re-start on the clutch. Is this an A/T vehicle? If so, there is a temperature switch in the engine coolant that is connected to the amplifier. The thermistor for evaporator temperature can be tested with a DVM.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Safe Crackin Sammy on Mon September 28, 2009 7:52 AM User is offline

There is a thermistor/thermal switch which is the next step in the process according to the factory service manual. There is also an "amplifier" that everything seems to tie into on the wiring schematic.

I believe I remember the condensor fan going to a higher speed but I will recheck that to eliminate it.

It is 4wd so I'll check the coolant temp switch also.


NickD on Mon September 28, 2009 3:20 PM User is offline

Had a 27" TV go haywire yesterday, remote operated the power relay, could hear it click on and off, but when on the screen was dim, off, even more dim. I pulled the relay out and opened the seal case. Dangest thing I ever saw, with the relay de-energized, contacts were still making, but with a very high resistive contact. With it energized, was more force on the contact pressure, so the resistance did go down. I polished the contacts to a mirror finish and set is working great again.

Never ran into that before, ever with relay contacts, in automotive, found contacts dropping up to 3 volts under load that kind of diminished performance. Also found erratic contacts, would close one time, but not the next. Typically contacts make better contact when cold. Just saying, you could have dirty contacts. Have also been known to replace mechanical contact relays with transistors with OV protection, they will last forever.

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