thaipaw

I have a 1996 4Runner Limited (Manual air-conditioning).
The air-conditioning blows hot at idle, but if I press on the gas a bit, I'll hear a faint click in the dash, then a second later the RPMs will increase by 500RPM or so, and the A/C will begin blowing cold.

I noticed this a few weeks after some amateur mechanics replaced a leaking head gasket. I'm not much of a mechanic, but where I live the "mechanics" aren't either. They forgot to hook up the cruise control cable after changing the head gasket. Is there something else they might have forgotten to hook up, or something they could have broken?

It appears that the compressor clutch is working OK. When a helper presses the gas I can see it lock up. It unlocks the moment he releases the gas pedal.

From a cold start, the engine idles somewhere over 1000RPM. Once it's warmed up, the engine idles at 700RPM in Park or about 550RPM in Drive.

Pressing the A/C button causes no change in engine RPM, but turning on the headlights causes the RPMs to fall a bit and then go back up to idle.

What is the "click" I hear in the dash? I guess it's a relay, but why is not actuating until I raise the engine speed? If I tear into the dash somewhere, I could probably find this relay. If I short it out, then would that leave the A/C on all the time?

I'm not sure how to troubleshoot this because I don't what the dependencies are in this system. Is the engine not idling up because the compressor clutch is not engaging, or is the compressor refusing to engage because the RPMs are too low?

What's my next step?

wyoming9

iTrader: (1)

Be nice to know where you live??

Who knows what they might not have hooked up correct .

Does your blower motor work at idle??

There is a signal from the igniter to the AC amplifier.

I have the 94 and 97 Factory service manuals there is a difference in the way the AC idle up circuit works not sure just what style yours is.

What is happening for some reason when the AC switch and blower motor are on the engine is not going to high idle so the AC amplifier does not power up the AC clutch.

Something is not hooked up no doubt or hooked up wrong.

The early style had a VSV (vacuum switching valve) to keep the idle higher might not be hooked up or hooked up wrong.

Then there are also the normal pressure switches good idea to really not try and hot wire your AC

That could cause all sorts of carnage !!

Speaking from my misguided Youth Compressor seized belt came off took out the other two belts .

Was not fun lesson learned!!



I take it your AC worked good up to when the head gasket was done??

Is this a new vehicle to you and your just working out the bugs??

Just what engine??

thaipaw

Hi! Thanks so much for the reply.

I'm an American living in northeast Cambodia. Until recently 95% of cars here were imported second hand. I'm reasonably sure this one came from the U.S. (the speedo is in MPH). I've had it about 7 years and it's been great. When I bought it, it was still on the original tires and even now it's only at 120,000 miles. Six months ago I couldn't get the mechanics here to fix the brakes or the A/C so I drove it to a Toyota dealer in Thailand for repair. (The Toyota dealer in Cambodia will only work on cars that they've sold new.) They struggled a bit to find parts, so their repairs might not have quite been stock, but things worked fine for 4 or 5 months.

Yes, the blower motor works fine. At idle it blows hot, but when I step on the gas (whether parked or moving), it gets chilly in a couple seconds.

Where is the AC amplifier or VSV?
I unplugged/plugged all of the wires at the top of the engine around the throttle. I thought one of those looked like the VSV I'd seen mentioned on some other forum discussions.

I think the engine is the 3.4L V-6 5VZ-FE.

Thanks for the warning against extreme experimentation. I've been considering it, but would rather not follow through with it, though the cool season is over and day time temperatures are in the 90's now.

ajs_yota

Could just need a quick charge of freon. May be too low for the sensor to detect until you gas it.

thaipaw

@ajs_yota: I don't understand how being low on Freon could prevent the compressor clutch from engaging only at low RPMs. How would pressing the gas pedal increase the pressure of the Freon?

tns1

I believe there is a pressure sensor to prevent the AC clutch from engaging unless there is sufficient pressure in the system. This protects the compressor, which can be damaged by staying on all the time vs the normal cycling on and off in a closed system. It also prevents moisture from being pulled into system, which is bad too. I am getting ready to recharge mine, so I have been reading up.

This does not answer the question, since pressing the pedal can't cause the pressure to increase without the clutch already engaged. It has to be related to either vacuum, or RPM, or some loose wire connection. I'd tend to guess the last one. Pull apart any wire connectors, spray contact cleaner (or WD40), and plug back together. Some of those sensor connectors are a royal PITA. Make sure they are on securely.

vasinvictor

iTrader: (3)

I know when swapping a 3.4 into an older gen, there's an A/C idle up VSV. It allows a controlled vacuum leak to raise the idle when A/C is on. On the older gens there's actually a small screw behind the glove box, on the A/C amplifier that adjust the rpm at which the A/C compressor will engage. I'm quite sure the newer gens don't have that. I'd try to find a a VSV that wasn't plugged in, or a vacuum line that feeds the VSV that was plugged. I don' thave a link to a FSM handy for yours but should be easy to identify the idle up valve with one.

thaipaw

An update--A mechanic replaced the ECU (engine computer) and it fixed the problem.

Cactushead

I am having the same problem. It is in the 90's here and I pull out from work and sit at a red light for about 5 minutes. The A/C will blow warm and sometimes the idle starts jumping up and down with a clicking under the dash. I put it in neutral and give it some gas and it is fine. Could the idle just be too low?

thaipaw

My friend's '96 4Runner was idling around 400RPM and the A/C worked fine. Even when mine was cold idling at 1000RPM the A/C still didn't engage. But, like you, putting it in neutral and giving it some gas to about 1500RPM would cause the A/C to start.

Another thing I noticed -- If I downshifted on a long steep hill, the engine would be around 3000RPM but still the A/C would be off, so it wasn't simply an issue of engine speed. It seemed to be connected to the gas pedal position.

My mechanic said that changing the computer fixed it, but then he also changed a few other small parts in the A/C system, because he said that it still wasn't "cold enough." I had noticed no other computer-related problems and it seems odd to me that the computer could fail in such a way to cause this one small problem with the A/C, but that's how it looks.

I wonder--is it possible to have someone reprogram the computer? Perhaps some of its programming got corrupted, so it doesn't actually need to be replaced? I saw a reference in another forum to Toyota reprogramming an ECU, but I don't know anything more about it.

Cactushead

This is one of those things I dread taking it in for. They will "test' for hours and say they found nothing and it ran flawless....

Team420

$10 for a recharge can. Thats always the 1st place to start. Many many times I have seen the ac not blow cold at idle, or just blow cool, but once ya get rpms up, it blows colder, and almost every time, just adding more refrigerant solved the problem.

Cactushead

Never did this. Is there a DIY?

thaipaw

In my case, I could see that the compressor clutch was not engaging until I gave the engine some gas. If the compressor is running at idle but the A/C is not cold, then Team420 gave the right advice (though if you're low on refrigerant you probably need to check for leaks and may need to replace the accumulator too). I thought the DIY kits were banned in most parts of the world because of environmental issues.

mwisham

The last thing you should do is add more refrigerant. If it is low, that means there is a leak that needs to be fixed before putting more refrigerant in. It will also need a good vacuum pulled on it to remove any air or moisture from the system. Those stupid A/C Pro commercials have everyone thinking all they need to fix their A/C is to throw a can of freon in it. Low freon is only one of many causes of poor cooling and often that is not the problem at all. Too much refrigerant will cause high head pressure and premature compressor failure. If you don't have a set of guages and a vacuum pump, please take it to someone that does.

Cactushead

Not sure if it was mentioned but when I have the fan on high I can hear it slow down a bit when I am off the gas. Is that normal?

94 Newbie

If you are referring to at idle, and when the RPMs are too low anyway, than I would say YES just because the alternator is probably not spinning fast enough to keep up with the voltage requirements.


Britt