Toyota 87 4Runner A/C disengages when engine comes up to temp

[SLC97SR5]

Alright, this is not your standard "my A/C won't work" thread.

Here's the vehicle specs: '87 4Runner 22RE, V6 radiator, W56, 4.7's, 5.29's, factory A/C, fresh tune-up w/factory parts, usual mods...

I've owned the 4Runner for 3 years and it's finally time to get the A/C working. It was inop when I bought it, no charge. I converted it to R134a and replaced the reciever/drier. I pulled 29" of vacuum for 5 hours. No leaks noted.

The issue I'm having is after my engine comes up to operating temperature the AC clutch disengages and will not re-engage until the engine cools off.

I remember a thread that someone said there is a engine overtemp cutoff swtch for the A/C...I can't find that thread. Regardless there is no mention of switch in the FSM.

I have verified that I have proper referigent charge, the belt is tensioned, the pressure switch is closed, the thermistor in the evaporator is functioning, the dash switch works, A/C relay is working, no blown fuses.

I have tested the ECT (engine coolant temp) sensor, the cold start injector timer switch, the engine temp gauge sender, the temp sender atop the water neck.

What is killing my Air Conditioning?!

The condensor gets hot, like normal but I can place a box fan or the hose on it and it cools off like driving down the highway.

The FSM says to test all circuits that feed the A/C amplifier and if they test good, to replace the amp. I have adjusted the RPM knob and it works. I inspected the A/C amplifier board for cold solder joints, corrosion, burnt components, broken pins...nothing. Looks great.

When the clutch kicks out on the compressor the coil on the A/C amp is still energized.

Any idea which way to turn the RED knob for cooler or warmer air?

Is there an overtemp sensor on the engine?

Does the ECU have control over the A/C? I cant find anything that indicates that.

The only temp sensors I'm aware of are:
Evaporator thermistor
AFM IAT sensor
Gauge coolant temp sender (between intake runners 2/3 single spade )
Cold start injector timer switch (brown plug under intake)
Engine coolant temp sensor (green plug under intake)
EGR sender on top of water neck


I'm up for any ideas, this 4Runner is black and UT is running a bit warm this Summer

Cliffs: A/C works until engine gets to temp. Proper charge, sensors seem OK.

 

[Raleigh]

It is one of several things.

1) plugged condenser coil not transferring the heat load from the compressed gas. This will cause high head pressure which will shut down the compressor actuator.

2) Plugged metering device, this will cause low pressure return to the compressor and also shut down the actuator.

3) Plugged evap coil, this will also cause low pressure and the coil will start to freeze up.

Only way to know is gauge up and see what the pressures are doing before it shuts down.

 

[SLC97SR5]

It is one of several things.

1) plugged condenser coil not transferring the heat load from the compressed gas. This will cause high head pressure which will shut down the compressor actuator.

2) Plugged metering device, this will cause low pressure return to the compressor and also shut down the actuator.

3) Plugged evap coil, this will also cause low pressure and the coil will start to freeze up.

Only way to know is gauge up and see what the pressures are doing before it shuts down.

1- There is not a high pressure safety switch. High psi cannot shut it off, only blow lines/components.

2-The low side gauge indicates 30-35 psi when the clutch opens. There is no voltage present @ the clutch signal wire yet the low psi switch remains closed.

3-Perhaps, but the thermistor is still within range and there is no visible ice on the evaporator.

 

[jentzschman]

Might be the expansion valve. That is what tunex said was wrong with mine. Mine would work fine as long as I was not driving. AC worked for over 15 minutes while my truck was parked.

Once the RPM's went past ~1500-2000 the pressure in the system would rise and the ac would shut off.

I plan on pulling the cooling unit and replacing the valve. Lucky for me they left the system un-charged so it will be easy to pull and replace. Then I will have it re-charged and hopefully that will solve my issue anyway.

Hopes this helps.

 

[SLC97SR5]

I found my issue, here is my thread from pirate:

http://www.pirate4x4.com/forum/showthread.php?t=1078908

After considering everyone's advice and hitting the FSM again I determined that the system was functioning correctly and I must have missed something.

I pulled out the meter and started looking for voltagesfrom theclutch backwards.

I noticed that the clutch DID have voltage present, even when prematurely disengaged.

The issue ended up being a dirty connection from the AC amp to the clutch. When the clutch and electrical plug got hot, voltage dropped from 14vdc to about 10vdc. I removed the old corroded plug and hard wired the clutch. This helped but it stillkicked offlinesoonerthan itshould.

Soooo, I went back and re-read my thread. I decided to check the clutch's air gap. Spec is .6-1.0mm. Mine was set at 3mm!! No wonder it could not stay engaged. I removed the clutch and found ati-seize and a USA sticker, definetly not a factory unit. I removed the excess shims and set it down to 1.2mm.

Although the gap is a bit large it works perfectly. I have adjusted the red pot on the AC amp and have nice, cold air. Duct temperatures have been 28-30* while moving and the compressor cycles as it should.

 

[ricsrx]

Nice work, my truck is next!!

 

[SLC97SR5]

Thanks! I put some serious time into it. I'm pumped it paid off.
I hopped in it the other day after sitting in the sun and the cab cooled down to the point that I could reduce blower speed after 15 minutes.