Importer

Hello all!
My name is John, and I have the unfortunate addiction to restore/rebuild vehicles. I recently bought this neglected 1994 Lexus SC300 to restore and make my daily driver. But I've ran into a couple problems.
1. Overdrive does not work. Only shifts to first 3. Although I think it's shifted to 4th at one point, then the "O/D Off" light started flashing. May have to swap transmission with another automatic later on, or 'consider' converting to manual. Whichever is cheaper.
2. Climate control screen is broken so I can't use the self diagnostics feature. (Auto + Recirculate then ignition). Although I do have a new unit I got from the salvage yards which I will install later on when I have some more free time.
3. Brake Pedal goes to the ground before actually engaging. I've bled the brakes already, and we suspect it's the master cylinder.

And my biggest gripe, since Texas is HOT.
4. The AC clutch does not want to engage. No solution YET.


Ok, introduction's over. Down to business.
So at first the fuse for the Climate Control was removed because the past owner thought the unit stayed at heater. Fortunately I figured out the past owner just didn't play with the car enough to figure out it's controls. Unfortunately the screen on the climate control unit is half broken. So I can only guess what's it saying. Although I did figure out I can set the AC to do auto, which will allow me to do max AC or turn on heater, and I can just control the fan speed via buttons.

So what I've done so far is, well. Add more R134A into the system. I assumed the pressure was low, so I bought a can and started loading it. But I noticed the system was at 65-70psi on AC compressor idle which I would assume would tell the switch that there is enough refrigerant in the system to operate the compressor without damage. So right now I'm assuming there are no leaks in the refrigerant.

Then I noticed that the compressor was not even connected to it's harness, and so I tried plugging it in and well. AC clutch still wouldn't engage.

I then started checking the the Magnetic Clutch Relay and the relay is in fact functional.

At this point I'm stuck on what to do next in regards to the AC system, So I'm hoping I could find the solution here, I've searched the forums and read the service manuals for my other vehicles, and I can't put my finger on what the problem is. Is there any other fuses I should check?


Any help would be highly appreciated!
Thank you!

Importer

UPDATE: I can get the compressor to work by jumping 3 + 5 on the magnetic clutch relay. I refilled the refrigerant to the correct pressures, and am now getting cold air. But I am not gonna leave the ac compressor stuck on.

So I can verify
-AC Compressor works
-Magnetic Clutch works
-Magnetic Clutch relay works

So I'm guessing now I should check the AC low pressure switch?
Is there a way to test that out? and is there a high pressure switch on this car?

Importer

UPDATE:
Installed the new Climate control unit, and the only code showing up is code 11.
Turns out pressure sensor is functional, and working.

I've been reading up on the service manuals and I got try the first test. Where I have to check the voltage between two points and I got a voltage of 3.7, where as in normal temperature, the voltage would appear at 1.8V-2.2V at 77 degrees ( and for reference 1.2V-1.6V at 104 degrees) voltage lowers with temperature increase.

So my assumptions now are that the AC unit thinks that it's really cold in the interior, therefore not engaging the Compressor clutch.

I'm currently looking for the location of this "Room temperature sensor".
After I test this sensor, I'm hoping it is faulty, because the next thing would be looking for a short or cut wire in the wiring harness.

Will update soon. For the benefit of other members.

Importer

UPDATE:
Checked out this Interior Temperature Sensor, and turns out it was disconnected.

Unfortunately that did not fix the problem. Compressor still will not engage
An odd discovery though, the low power sides of the magnetic clutch relay is actually hot. So I tried bench testing and have discovered that the ground provided in the fusebox is a bad ground, if I run the postive to one end of the relay and just ground the other side to the body, the relay will engage.

Problem:
Bad ground in the relay.

Solution:?
-Ghetto rig, and just run an external ground into one side of the relay
-Disconnect battery and disassemble the fusebox figure out why the ground is bad.


Honestly if ghetto rigging will work just fine, I think I might opt for that.
My only concern is that what if the negative side is the side that has the switch for the circuit.

Anyone wanna chime in at all?

Flyinggobl

Do you have a pic or can tell me the side of the relay to ground

Importer

This was a long time ago. I did actually use some sort of ghetto rigged timer to cycle the compressor clutch on and off every 20 seconds.

Afterwards i found out the ECU was the cause of all my problems. From the transmission not shifting through all of its gears to the AC Magnetic Clutch relay not getting the signal ground to activate.

I've sold the car over a year ago and therefore can't recall which pin I used to force the magnetic clutch to ground and then engage.