MrReeves99

Hi everyone
I'm having an issue with my air conditioner. '96 es300.

For a little background, It's been a couple years that the A/C would quit when it reaches 90-95 degrees out, especially in direct sunlight. Not a great thing here in southern California, where there's plenty of that. Whenever this happened, the air conditioning wouldn't run again til the car itself had a chance to cool off, usually overnight. Once or twice, I'd been running the A/C and it automatically shut off because the outside temperature dropped below 70 very briefly, due to the coastal climate, and it wouldn't start again until the next day. Long, sweaty road trip. Sometimes all it would take is heading into a store for a few minutes to kill the A/C, but if I left the car running, I could sometimes get it to hold out longer, sometimes for a few hours.

A recharge didn't fix it, So I "decided" that the system was dying, and rebuilt the whole thing (compressor, condenser, evaporator, expansion valve, drier) and had it re-oiled and recharged at the shop. It worked beautifully for a day, a cloudy day, and then the following day, the bright sunlight hit it, and it immediately cut out. This time, though, the green A/C light started blinking. And now, leaving it overnight didn't fix it. It seems stuck this way. However, it would run for a few seconds before cutting out, so I knew it was cooling. If i pressed the button on and off a bunch of times in a row, I could actually cool down the car a fair amount.

No matter what, though, the blinking light comes back, and the magnetic clutch disengages the compressor. Most online resources (generally camry specific) suggest it's the magnetic clutch relay, so that was the first thing I replaced. No dice.

The service manual says that the blinking light can mean one of two things: compressor not operating at engine rpm due to belt slippage or excessive pressure, or failure of the engine rpm sensor. So, I had the shop double check the pressure and it was just fine. Makes sense. They thought it was a faulty control unit, which sounded right, so I picked up another one at a junkyard, but I had the same exact issue with a blinking light and the magnetic clutch disengaging.

I was determined to avoid replacing the rpm sensor, which means discharging the recharging the entire system to remove the compressor. Not cheap. The sensor itself is already $100 or so.

So I got out my multi-meter and wiring diagram to see if I could trace the problem. With the connector to the compressor disconnected, the ground wire (black and white) reads 30 ohms of resistance, and the signal wire that goes to the A/C computer gives no reading whatsoever.

With the connector connected, the black and white ground wire, which goes to the signal ground pin, reads 30 ohms, which doesn't seem wrong, necessarily, because it first goes through the air inlet control servo motor before reaching the computer. From the wiring diagram, it seems likely it would add resistance... but I really don't know. The signal wire reads 130 ohms, which I'm guessing means it has a path to ground through the rpm sensor and then the compressor. I could be wrong there too, though. The rpm sensor alone gives a reading of 115 ohms or so, which, according to the manual, is within normal limits.

Right now my best guess is that the A/C computer's ground wire got disconnected or messed up somewhere? Or that I coincidentally got two bad control units? Really not sure.

Would mixing up the polarity on the sensor wires do this? There's a chance I managed to do that when installing the old sensor on the new compressor.

And, not to be paranoid, but I've had *mystery* electrical issues for a while, like check engine lights with no code, random codes telling me the transmission solenoid is malfunctioning, while the car shifts just fine, a lamp indicator on the instrument cluster but no lamps out, etc. The ghostly check engine light about the transmission solenoid seemed to happen most often when I hit a steep hill with the A/C running. If I cleared the codes, it generally didn't come back, and hasn't come back at all since I rebuilt the A/C system. The stereo is incredibly noisy, too. The alternator whine is so loud that I had to install a noise filter.

Anyone had this problem before? What's going on?

Arsenii

Hello,

Sounds interesting.. Try going into the diagnostics mode for the Climate Control, here is how to do so. That mode will allow you to see what error codes are stored in the system, which there must be some at this point. From your description, it seems like the system detects a critical malfunction and shuts the A/C off; the fault like that can be caused by pressure switch, evaporator temperature sensor or their wiring. You can also look into the refrigerant window, just to see if it flows right, it shouldn't have neither any bubbles nor straight liquid. In any case, start by checking error codes and go from there..

Hope this helps and best of luck!

MrReeves99

I should've mentioned this already, but I've run the diagnostic mode on the climate control unit and it returned the "00" normal code

I've done some more investigating meanwhile and found what seems like an abnormally high resistance of 20 ohms between the climate control unit ground point and the battery negative terminal. Everything else seems normal (ground to frame, sensor ground to climate control unit ground, etc.)

I came across this thread as well:
https://www.clublexus.com/forums/ls-...ng-issues.html

Has anyone had this issue with the es300? Could that be causing all these various problems?

Arsenii

It seems like the Black-White wire is what actually powers the clutch, it is not Ground, Ground for that clutch is supplied by the body itself, there is no extra wire. To make sure, check the resistance between that wire and a Magnetic Clutch Relay, here is a fuse diagram.

If you have the manual or a wiring diagram specifically for 1996, you can connect to every sensor for the A/C system right on the connection to the A/C Control Unit, which will show you the data that is seen by it. Since you know it is not a unit at fault, that could yield some useful information. I only have a manual for 1993, and I cannot confirm for sure that it has the same wiring setup.

Check that the pressure switch has continuity between Pin 1 and 4 up until the A/C disengages, which will prove that it is functional, and the pressure in the system is not the cause of A/C system failing.



Also, if the mechanic you've been visiting has an oscilloscope or even a graphing multimeter, you can easily check the speed sensor on the compressor - you should see 4 pulses per each revolution, you can check those readings and compare them to a tachometer.

Hope this helps and best of luck!

MrReeves99

The oscilloscope option has come up before, could be worth a shot, that's a good call.

The speed sensor connector has 3 wires, a signal ground and a signal wire for the speed sensor, and there's a third wire for the magnetic clutch relay, as you've described. I can see and hear it engaging and disengaging, but that doesn't rule out insufficient current or something like that

But I don't think it's the system pressure, per se, I've had it double checked by the mechanic, who even evacuated and refilled the system, and they also concluded it was an electrical problem. Could be that the pressure switch itself is faulty, so I'll test those pins on the connector when I get a chance.

I'm also working off the '93 wiring diagram, but have ordered the '96 version, which should arrive soon

Thanks!

Arsenii

The chances of it being a mechanical flaw are pretty slim, when the whole system was replaced and checked multiple times, the chance of missing something is pretty much nonexistent, so it would be a good indication to start looking somewhere else.

One vicious method of verifying that all the mechanical components are functioning properly is to power the clutch straight from the battery and check that the system is functioning normally and the pressure stays where it should. That said, only try it on your own risk, since there is a reason why the control unit keeps disengaging it after all, even if it is caused by a bad connection somewhere..

To rule out insufficient current, you can check for a voltage drop between the clutch and a Positive battery terminal, if there is some, it may indicate internal damage to some wiring, but as long as it is less that about 0.1-ish volts, it shouldn't give you any issues. You can also put something like a low power headlight or fog light bulb instead of a clutch to see how bright would it be.

Even if you don't have an oscilloscope, there are some units for about $20, while you won't get any precision from one, those should be sufficient to check the signal. Below is the link to one, I am yet to try it myself though..


Hope this helps and best of luck!

MrReeves99

Edit: Nevermind

MrReeves99

Here's an update: I checked the voltage of the pressure switch during operation, and it seems not to do anything at all. When testing the PSW terminal to body ground, rests at 0v when I engage the compressor clutch. When I unplug the pressure switch, the blinking light on the climate control unit goes away, but the clutch does not engage.

I tried to test continuity between pins 1 and 4 on the switch, to see if it closes/opens when the AC pressure changes, but with it unplugged, the clutch won't engage at all... so how am I supposed to test that? Do I have to jump the connector?

MrReeves99

I jumped the connector, pins 1-4, and the problem with the blinking light and clutch disengaging persisted

Arsenii

What do you refer to as PSW Terminal?
Did your cooling fan engage at all when you disconnected the pressure switch?

A/C is not supposed to engage without pressure sensor, since it is considered to be the worst of emergencies.

All that remains now is to wait for a 1996 wiring diagram and start blindly monitoring all the sensors linking to the A/C System straight from the Control Unit. I would start with an RPM counter on the compressor, though even that is supposed to trigger a Fault Code.

Coming to think of it, try forcing the Control Unit to throw a fault code by disconnecting a Coolant or Ambient temperature sensor, from the ones that are in relative reach. See if the Control Unit is actually throwing codes to verify its operation.

Hope this helps and best of luck!

MrReeves99

It does currently show the 21 solar sensor fault code if it's sitting in the shade

By PSW terminal I mean the pin on the back of the climate control unit where the pressure switch wire goes

I also noticed that the sight glass stays cloudy, maybe it doesn't reach enough psi to flip the low side switch?

Arsenii

Sounds like a dead end in that direction..

Was the pressure checked when the system was running?

It could be true actually, but then you ruled it out by shorting Pins 1 and 4. Try checking that those are shorted on the Control Unit, just for kicks.. Below is a video of how a sight glass should look like when the system is fully charged..

MrReeves99

I reconnected the pressure switch for the sight glass test

And when the rebuilt system was initially recharged and serviced, it ran just fine for a day or so, so I assume the pressure was checked with the system running as well

I ordered a new service manual with wiring diagram for the 96 and an oscilloscope, wish me luck

Arsenii

I just thought of it, sorry I failed to mention it before, but Toyota themselves actually offer all the Service Manuals for Toyota, Lexus and Scion vehicles, here is a link to it. For $20, you get a 2 day access to all the manuals listed on the website directly from Toyota, including Wiring Diagrams. I seem to have all the manuals I need so far, so I never got to try that service yet, hence it kinda slipped out of my mind..

Best of luck!

MrReeves99

Well I got the oscilloscope hooked up to LOCK IN and SG with the compressor running for a short amount of time (before it automatically disengages) and it didn't show much of anything. Looks like my fear of a busted rpm sensor may have come true.