i'd like to know how badly this affect the A/C?... mine works until it doesn't which is about 20 minutes... i've ordered a relay for the mag clutch and really don't want to tear out the dash to replace the sensor... is there another way?...

 

Hello,

As discussed many times around this forum, Code 21 will get tripped in the A/C Control Module every time the Lighting around it is Insufficient, or simply put, you will always have that Code stored in the system unless you are in Direct Sunlight and have reset the system by pulling the ECU-B Fuse for a minute or two. That is a normal operation for those Sensors, it's even specified in the Service Manual, the point of something like this never fails to escape me though..

It seems like the reason your A/C System keeps shutting off after a while is due to Pressure climbing up so much that it trips the Pressure Switch, disabling the System. This could be caused by several factors, but one of the more common causes being the Condenser under the Hood not getting Sufficient Cooling, either due to a Cooling Fan malfunctioning, or a layer of Debris forming between the Condenser and the Engine Radiator. A way to test it is to get a Sprayer and fill it with Cold Water, once your A/C System stops working, spray the Condenser with said Water, cooling it down, which in turn should cause the A/C System to start back up until the Condenser heats up again.

Hope this helps and best of luck!

 

Thanks... i've test the sensor in full sunlight... i've pulled ECU-B... i don't know what issues the faulty sensor can make though to the operation of the A/C... i think you're right about the the condenser... i purchased relays for the mag clutch and beside it's position in the fuse box is a socket for a relay labeled as fan 2 but no relay is in it?... i'l look over the engine... i had the radiator replaced and at the same time my refrigeration system recharged and checked... but it still didn't work correctly after the shop... i didn't return it to them because i was gone for a month and then the weather was cool enough so i didn't need it..

 

I decided to recheck the magnetic clutch relay by removing the cover from it. i wasn't able to simply pull it by hand (pliers will help) but removed the cover from it and was able to see carbon residue on one side of the cover right above the contacts that look as they are worn and arcing... i think the relay is my problem now..

 

Common failure the relay contacts take a beating due to the large magnet and the resulting current kick back.

 

I love to know why.... thanks...

 

the replacement relay is like over $60... and there isn't a stock sun load sensor in the universe..

 

In broad terms, any piece of Wire twisted into a Coil turns into a Choke - much like a Capacitor it can store some Charge, the difference however is that Choke is always desperate to get rid of it the moment the Power stops flowing through it, if you simply Disconnect the Coil from the Power Source, the Voltage inside of it will keep Increasing until the Charge stored in the Coil can find its way back to Ground, one way or the other. This is how Ignition Coils work, and it's also a core principle behind the operation of Buck or DC-DC Converters. Below is a video that goes in a bit more detail.


In case of the Relay though, this means that every time the Switch turns off, the Coil inside of the Compressor Clutch will Discharge through that Switch, usually with a noticeable Spark, which not only creates Soot that inhibits the Contact, it also physically Erodes the Metal, that is how EDM systems work. Not sure why they don't do it with the Clutch Relays, but on any other Relay that controls a more or less substantial Coil, they will attach an additional Ground Connection to a Relay, such that instead of having a Relay Switch simply hanging in the air when the Relay is Off, it will Flip from Power straight to Ground, providing a safe route for the Charge in the Coil to escape without damage to the Contacts.


Huh, I thought you were checking a wrong part number at first, that is until I went looking for it myself .. that's a lot of money for a relay..

Seems like your best bet would be Junkyards in this case, at least the good news is it appears that Toyota still uses the same exact Relay to this day, or at least until very recently, so it really won't be a problem to locate. Here you can find a list of cars it was used in.

Again, the Light Sensor is really not that big of a concern, at least in the A/C System, it will not cause your A/C to cut off at random, I would just leave it alone for the time being, in fact I did as I have the same exact code stored in my car, as I am pretty sure about 90% of other Lexus models of similar vintage..

Hope this helps and best of luck!