unknownowen

I bought a 94 4Runner recently with 4WD, AT and the 3.0 3VZ V6. The air conditioning has been out for years and no one has bothered to fix it apparently. I took it to a shop and had it refilled with R-134a nice and tight. No major leaks were detected.

The AC would still not start unless the shop jumped the clutch straight from the battery - then it blasts ice cold air!

The tech suggested that the dual pressure switch or AC cut-off relay could be the issue.

Using a old Chilton manual I think i have identified the AC relay and pressure switch connector. I tested the relay operation and it seems to work fine but decided to jump it anyway. I attached some pics of my jumper connections. For reference: the AC cutoff relay is jumped by white, and the pressure switch connection is jumped by red. In both cases I jumped red/green to blue/white. The system still does not come on. AC switch light comes on and is solid, and the 10A fuse and 40A breaker both check out fine. Any other suggestions? I think the actual pressure switches are inside the evaporator box yeah? Should I open it up and do something in there? Anything else I should check out?

aztoyman

Never had a 3.0 but most pressure switches are in the evap box. The wiring pig tail sticks out though. Maybe you can test it from there. You also have the A/C amplifier in that area.

Maybe someone with a 3.0 will chime in to give better details.

j2the-e

I don't think my truck has a pressure switch. There are no pressure switches in the evap box. Do yourself a favor and get a factory service manual and wiring diagram. If you can't find one elsewhere, you can print whatever you need from this site: www.techinfo.toyota.com. You click subscribe and buy a 2 day subscription. Get yourself a fresh ink cartridge and lots of paper

aztoyman

My 88 22RE pickup had the switch in the evap box and my 99 4Runner donor had it in the box.

It's got one in the system somewhere.

Punchy

There is also a reley set in the engine compartment (Hanging off side of fuse box) that also controls the clutch and there is a small knob on the cooling element housing that is for RPM cut off, If its messed with and turned to high the AC pump will never turn on, Needs turned other direction.

RJR

This is a situation where you really need to get the factory service manual and the wiring diagram. You'll waste a lot of time tearing stuff apart and making wrong choices otherwise. With the wiring diagram and a multimeter, you should be able to troubleshoot it down to the failing component pretty quickly.

As a summary, here's what has to work in order for your compressor to start turning.
- 40 amp heater fuse is good
- 10 amp AC fuse is good
- If both of these are good, the little green light in the AC switch will come on when the blower is on and the AC switch is pressed.
- Pressure switch says the system has valid pressure (above about 30 psi and below about 200 psi)
- If you have an auto tranny, the AC cutout relay and the water temp switch have to both agree that it's OK to turn on the AC
- Ignitor circuit sends an "engine running" signal to the AC amplifier
- AC amplifier (a black box behind the glove box) combines the various signals listed above to drive the compressor clutch.
- AC amplifier powers up the compressor clutch and you get cold air.

As you can see, there's a lot going on in this system, so do some systematic troubleshooting and save yourself a bunch of time and hassle.

scope103

All true, and not that hard. http://personal.utulsa.edu/~nathan-b...ditioning.html

j2the-e

Ok, I feel dumb right now. Took my own advice and looked at the manual. Pressure switch is in the evap box. Sorry about that

unknownowen

Thanks RJR. I do have the wiring diagram the tech printed for me straight out of the factory manual.

Looks like the AC amplifier and water temp switch are my next targets. I'll fiddle with the knob and try to jump some circuits to see if it gets running.

RJR

My compressor blew up in a cloud of smoke last week, and blew the AC fuse (which is why I've been studying the circuits:-() I'm assuming that the compressor seized, causing the magnetic clutch to slip and overheat, which melted down the coil, blowing the fuse. I'm hoping it only took out the magnetic clutch, and not the AC amplifier. I haven't had time to thoroughly troubleshoot it yet.

The AC amplifier looks expensive, so I hope for both our sakes that's not the problem. I don't know what's inside it, but I'm guessing probably discrete transistors, diodes, and relays. If one is good at electronics, it might be repairable if it is malfunctioning.

RustBucket

iTrader: (1)

OP, I did the exact thing as you a few weeks ago. The compressor would pull in only intermittently. I ended up unplugging and replugging the AC switch connector and then it worked perfectly. Must have been a loose connection.

unknownowen

Update: It was the AC cutoff relay. I identified the zero voltage circuit through there from the AC amplifier connector, and the pressure switches worked fine.

I jumped 1-3 and 2-4 on the cutoff relay and the AC works fine now. It's strange because I already took the relay out and tested it, and it worked correctly when voltage was applied on the circuit.

What could be causing the relay to cut out? I've fixed the symptom but there's still a problem, I guess. I don't think a new relay would fix the issue.

RJR

Sounds like the relay coil isn't getting actuated. The relay could be just fine, but if the coil drive signal is missing, it's not going to work. I agree that a new relay is probably not the answer. You need to check the coil drive signal, and figure out where that's getting lost.

The AC cutout relay coil is driven from the water temperature switch. which is located on top of the engine at the back. Not easy to get to, I don't think.

scope103

The cutoff relay (present only on 4wd) temporarily shuts down the AC when the coolant temp gets too high. It sounds like you've just removed the relay from the equation with your jumpers.

But I'm not sure. Unfortunately, the manual gives two different pin-outs, and different connector shapes, for the same relay. http://personal.utulsa.edu/~nathan-b...ng/21relay.pdf http://personal.utulsa.edu/~nathan-b.../2aircondi.pdf Do you know which you have?

If you have the one on this page, jumping 2 to 4 just tells the AC "pretend I'm a 2wd, and don't worry about the coolant temp." Fine, until you start huffing up a big hill on a hot day. But what about jumping 1 to 3? You're just shorting out the relay coil, which means that you're shorting 12v to ground when the Engine Coolant Temp switch says "cool enough." (which is what it should say when you first start the truck). If the Temp switch was closed, jumping 1 to 3 should have blown the Gen fuse. If you didn't blow the fuse, perhaps your Engine Coolant Temp switch is broken (open), or maybe just disconnected.

The prior paragraph assumes you have this relay. If you have the other, it's a little more complicated, because you've just "jumpered" the relay coil into the contacts. The coil resistance may be low enough to trigger (turn on) the AC Amplifier, but that can't be good for any of the components.

You need to be sure you know the pinout of your relay, and because of the ambiguity in the manual you need to test it w/12v. It sounds like you did that; which relay do you have?

RJR

Either way Scope103, since the relay checks out on the bench and he didn't blow anything up by shorting the coil, I think you're on the right track when you suggest the water temp sensor isn't working. That should be easy to check when the engine is cold - there should be continuity from the relay coil to ground.

The AC cutoff relay is only present with an automatic transmission. I assume the extra load of the auto tranny led the Toyota engineers to add that extra level of protection. Seems you could get by without it if you just watch your temperature gauge.

scope103

That is also my understanding; automatic and 4wd.

I would seem that way, wouldn't it? But isn't that pretty much what everyone who has blown a head gasket once said?

True, but which pin is that? I'll bet that unknownowen did NOT rely on the ambiguous manual pinout, and tested the relay correctly. So he can figure out the correct pin to check for continutity to ground (the pin to the coil that does not go to 12v). And share that with the rest of us!

While he's at it, he can tell me which one of these two temp sensors is for the AC.

unknownowen

scope103,

I think that the two relay pinouts you showed me are actually the same thing. The one on page AC-30 shows the relay pins and the one on page AC-8 shows the connector slots for the relay. If you look at the diagram for #8 and compare it to the relay pins you can see 2/3 on the connector goes to 2/4 on the relay. Yeah it's confusing. But what I did was just jump the switch and relay coil. I didn't cross them over.

None of my fuses are blown so I think the water temp switch is indeed stuck open. I will do some sleuthing this week and figure it out. The pin to test is #1 in both cases. I'm just happy I finally have cold air!

rrussell14

I just replaced evaporator, exp.valve and hoses o drier also.I plugged the hole on the evaporator where switch is located with a tight fitting plug with o ring wired the wires together and by passed low pressure switch that was about 3months ago my a/c works great so far I am not sure if any long term affects I might be causing ??But so far so good .It was a lot easier than i thought .also Just make sure you have a LONG philps head and dont keep trying to remove lines at firewall when they will pull right through from inside with evap. coil .SORRY:1993 pickup 22r love my toyota Also all those parts were less than 100.00 dollors at Rock Auto .com AND NO I DONT WORK THERE but check out there catalog section

DocShock

[/QUOTE]

Hey guys, upon reading gobs of information this past week since buying my 94 4runner auto 4x4 (non-working AC), I think I have narrowed down my problem to the above one or two sensors located under the intake manifold on the top/back of the motor.
The one to the far left (the sensor, not the vacuum) is broken in half and not even connected (thinking that may actually be my problem, causing the compressor to not engage),
and the one to the far right (with 1 wire), today while fiddling with it, the wire broke off flush to the connector (it was corroded...not sure if that is related to my compressor not engaging but would like to go on and fix that connector..hoping I can get a connector from Toyota, if not will try to find one at a boneyard).

My question is, what is the sensor on the far left (i assume it is the engine temp sensor that feeds info to the ac cutoff relay) - hence the reason my compressor will not engage.
And, what is the sensor to the far right (1-wire connector)??

My system is tight/no leaks, or there is refrigerant in it (compressor not engaging so have not gotten an accurate pressure reading, but low side w/o engaging was around 70)
AC light in the truck comes on/stays solid..all fuses/breakers under glove box and engine compartment are good.

Also, when I get home, will run thru the various tests here:
http://personal.utulsa.edu/~nathan-b...19pressure.pdf
http://personal.utulsa.edu/~nathan-b...ng/21relay.pdf
http://personal.utulsa.edu/~nathan-b...ng/22airco.pdf

DocShock

And sorry, I know this thread is 3-1/2 months old..hoping one of the original posters can help me out!
Just wish it wasnt so dang dark when I get home from work now!! sheesh
Guess I could wake up at 530 and fix it, tho (I live in FL..not too chilly here, lol)