Brenjen

OK, here the deal - my A/C worked really good for a while, started suddenly blowing warm humid air. Let it sit for a while & it would blow ice cold again. This played out over a period of about 2 weeks last summer. After those two weeks up until now, the A/C might work for a few seconds here & there & it might not but pretty much was just not working.


Presently the situation is this; I took the cooling unit apart & tested the thermister & it tested good. I checked the amplifier for busted solder points or burned spots & didn't see any, I removed the A/C cut off relay & jumped the 1 + 3 socket together & the 2 + 4 socket & my compressor kicked on & the A/C worked. However; when I put in a new relay (thinking that was the problem) the A/C will not work so apparently it's not the relay afterall. With the socket jumped with wire the A/C works fine & will even shut off using the dash switch....what the heck am I missing here?

Is the amplifier bad? I thought for certain it was a bad relay & got all happy only to have my joy cut short. Help an electrical dummy out.

4Crawler

iTrader: (3)

Hard to say, but there are a number of switches/sensors that feed the A/C amplifier, so one of those may be telling it to cut off the A/C. It has a low RPM setting (via the knob on the box), and it has a low pressure cut out switch, and engine coolant temperature sensor and a temperature sensor that I think is in the A/c system some place. Any of those giving bad information could cause the amplifier to shut off the A/C. Maybe check those all out and see what is up. For example the low pressure switch can be jumpered temporarily to test it.

Brenjen

OK, I have been looking the schematic over & the A/C cut off relay is open until acted upon by the engine coolant temp switch. The engine coolant temp. switch is open as well & closes to ground which apparently means that if the engine coolant temp. switch senses overheating or fails that will energize the A/C cut off relay & shut down the elctro magnetic clutch on the A/C compressor. (the A/C doesn't work even when the engine is cold so it would have to have failed)

As far as I can tell by reading the schematic, the engine temperature control switch is the only sensor that acts upon the A/C cut off relay. So it must be a bad engine temperature control switch. Now I need to find out if that's the same thing as the engine temperature control sending unit & where in the heck it is so I can test it. I can just imagine it's probably under the freakin' intake plenum & will require the top half of the engine to be torn down to get to.

EDIT: BTW 4Crawler I want to say thanks; you are always very helpful to everyone & try very hard to go above & beyond when you don't have to & I'm sure it doesn't bring in nearly enough revenue to your site to pay you for the time you spend helping people for free. You sir are a credit to Yota-Tech & mankind in general.

4Crawler

iTrader: (3)

All the temperature senders/switches are different, i.e. they are not shared with the ECU or something. Generally there will be senders for the ECU, the temp. gauge on the dash and the one for the A/C at a minimum. On my '85/22RE, that sender is atop the thermostat housing, don't know about the 3.0. Should be in the FSM, although likely the A/C stuff is not as well documented. So you need to use the component layout diagrams to identify the other senders and then the ones left are for the A/C and other optional parts.

anotherjeff

Back to basics: Is there enough R134a in it?
Did you put your gauges on it? What were the pressures?
Or... Did you jumper the low pressure cutout switch?

I do not believe that there are any dedicated senders/sensors for a/c. When installing a/c, there are only 4 electrical connections: the compressor, the underdash box, the idle-up VSV, and the plugin dash switch. There are no sensors/senders in the "A/C Kit". 4Crawler, Are you sure that the sender on top of the thermostat is specifically for a/c?

Brenjen

According to the FSM online (tulsa.edu) for the '93; the A/C cut off relay is connected to the A/C dash on/off switch - the pressure switch - the engine temperature control switch (ETC) & the amplifier.

Reading the FSM schematic shows that the relay is connected to the engine temperature control switch (ETC) with one wire & the ETC switch is normally in the open configuration with the closed config. going to ground. Going by that, the ETC switch is what causes the relay to trip; it closes the circuit which then powers the relay, once powered the relay closes & that cuts off the magnetic clutch.

http://personal.utulsa.edu/~nathan-b.../2aircondi.pdf

Now; the amplifier & the pressure switch are shown to be downstream (so to speak) of the closed relay; so only the A/C dash switch (power) & the ETC switch (ground) can affect the relay & the relay affects the pressure switch & amplifier which in turn affect the magnetic clutch on the compressor according to that schematic....right?

4Crawler

iTrader: (3)

The pressure switch and thermistor feeds into the A/C amplifier and tell it that there is enough pressure in the system and that the temperature is in the proper range. So yes, they are downstream, so to speak, but if the A/C comes on and the pressure is not high enough, the low pressure switch opens and kills the A/C, via the amplifier and through to the relay.

I know on my '85, there is a dedicated engine coolant temperature switch, that is separate from the ECU temp. sensor and the gauge temp sender and the cold start injector temperature switch for the A/C. This is in the factory installed set up. Maybe after market A/C systems do not have the tie in to the coolant temp and likely they also do not tie in to a fast idle control like the factory system has.

Brenjen

I'm 100% positive my system is bone stock except for a little chopping on the wiring that was done before I got the 4Runner. So I'm pretty sure there is an "engine temperature control switch" on my truck as well since my temperature gauge works; I'm assuming this would be run by the Engine temperature control sending unit. My problem is, I don't know for certain; I also don't know for certain where either one of them would be located (unless it/they are under the plenum).

I can barely reach the pressure switch after taking the top & bottom of the cooling unit loose without taking the A/C lines off in the engine bay & removing the unit completely. If I'm going to have to do that I'd rather let a shop remove the coolant & do the work & I'm not prepared to pay that kind of money when my A/C is currently working with the relay out & the plug jumped.

I checked the low side pressure & I couldn't get a good reading...might be the cheap gauge, might be the fact I couldn't get my hand all the way down in there to press the fitting on. Either way I'll check the pressure if I can & jump the pressure switch if I can & see what I can come up with tomorrow.

Thanks for the help so far & I'll report back what I find.

anotherjeff

Oh! 3VZ-E 4WD A/T 4Rnr's do have some extra circuitry! The Engine Coolant Temp Switch and the A/C Cutout Relay (and a Condenser Fan) are apparently unique to those models. And, the Engine Coolant Temp Switch looks like it's under the plenum, like you thought (http://www.ncttora.com/fsm/1990-1995.../componen.pdf).

And, yes, it would seem that the Engine Coolant Temp Switch (I'd be careful calling this the ETC; usually reserved for the Electronic Transmission Control) could disable the A/C. But, an open Pressure Switch would do the same thing, and jumping the relay would bypass either one! I'm thinking that you're just low on coolant.

You might find the FSM at http://www.ncttora.com/fsm/1990-1995...5/contents.htm and http://www.ncttora.com/fsm/1990-1995....1990.1995.zip a little more detailed than the '85 version.

Brenjen

Thanks for the added FSM info! I was going off the '93 FSM on the above link, very similar if not identical to mine, since it has the 3VZE equipment listed. And as for calling the engine temperature control switch the "ECT switch"....for the purposes of this conversation it's understood to be quicker to type, that's the reason I typed it out longhand & put it in parenthesis after. I wouldn't do that outside this thread; but thanks for the heads up.

As far as the open pressure switch - I see now where the pressure switch ties into the coil on the cut off relay in socket #4. All I had noticed before was the connections at #'s 2 & 3 which would be downstream of the switch instead of the upstream from the cut off relays coil. That makes much more sense to me now - I was wondering last night how something not wired into the relays energizing side could cause it to trip. Looking at it with a fresh eye this morning it's clear as a bell, yesterday I was just dazzled by all the pretty lines


Adding coolant was my first thought BTW since before I got confused on the schematic I thought it was the pressure switch. I purchased a couple 134a canisters & a gauge but I can't get my hand down there good enough to get it on the low pressure port. After my kids get taken to their youth group trip I'll tear into it again.

Brenjen

Well the pressure tested good so it's either the pressure switch or the ECT sensor under the intake plenum. Thanks for the help.

attitude

I am having the EXACT same problem and have replaced the pressure switch (40 bucks, dealer only, and you WILL lose all the freon, it's not like a Ford) I jumpered two pins on the pressure switch connector and put a toggle switch on it until I finally read something new to try.

But when it works, it works perfectly. cycles at 40 deg with the thermister, everything. jumpering it with the toggle switch allow me to cycle it manually, but I can also turn it off on the dash.

I posted a question on here a month or so ago and got NO responses, so I am glad you are getting some good info. I am leaning toward the overtemp sensor. . . Let me know how your's goes.

Brenjen

Mine is one or the other I'm 100% certain. I'm not going to lose my freon because of the cost to recharge & I'm not going to take the intake plenum off anytime soon either. Jumping the relay works, my system pressure is good, my engine temp's are good & the A/C cools without anything freezing up so I'm leaving it this way until I absolutely HAVE to take off the plenum, if the switch tests good then I'll leave it even longer.

anotherjeff

Yours is a OEM R-134a system, is it not? ('95 4Rnr) Cheap, compared to R12! And, if a shop does it, they recover and reuse (and gouge you on the labor!).

Brenjen

Exactly, as it stands now it works fine with no down side & it's not costing me a penny. Cheap is in the eye of the beholder, personally I get pissy over .50 cents

mt_goat

My A/C cut off relay is bypassed (jumped). I had to do this because the 5VZ ECU doesn't use one. Appearantly its only used on the 3.0 with auto trannies.

paul29

Question > Where is the low pressure port on your runner , I'm having trouble locating mine. Thanks

jesuszarzuelo

In mi case after rebuilding the motor the A/C did not work at first an than out off the blue it stored to work, it did so for a wile about 2 moths or so, than it wood com on and off intermittently tell now the cloche on the compressor will not engage, works fine when i apply direct power to it and blows cold !! check the cut off relay it dos not check good when i did the test that the Toyota manual calls for so i bout another one, how ever its doing the same thing the cloche will not engage and the relay dos not pass the test, how ever when i punched the wire #3 of the relay to test for + the relay kicked in an so did the compressor it also works good when i jump the plug 1 to 3 and 2 to 4 off the cutoff relay.Any ideas???