A/C light flashing?? - Page 3 - Toyota

rando · #31 (**permalink**) 05-09-2007, 08:00 PM

It turns out that soldering the diode DID NOT do further damage to my relay -- I simply made a mental mistake when testing the relay on the bench, post soldering.

More importantly, with the case removed, I can confirm that the diode isn't shunting the kickback (i.e. I can see an arc every time the relay contacts open). Apparently I made a 2nd mental mistake since the diode as installed can't possibly redirect the EMF since it will always be reverse biased. The bypass needs to go to ground. There isn't a ground rail available to this relay, so the bypass diode will have to be installed elsewhere in the circuit.

I'll post an updated solution when I have it -- sorry for any confusion.

rando · #32 (**permalink**) 05-09-2007, 08:04 PM

Quote:

Originally posted by TechWrench
Those contacts are, with out a doubt, burnt. I'm hoping the fog light relay holds out until the new relay is available again. I think the original A/C relay lasted 3 years, so I hope we have some time before the next one fries.

I tried to capture a video of the arcing but, as expected, it's too fast to be caught by my digicam.

Kmvreter · #33 (**permalink**) 05-09-2007, 08:44 PM

Thanks for the update Rando. I was wondering about the way you wired the diode but wasn't quite sure myself. Now we know.

So I went to poke around under the hood and look in the fuse box. Turns out I don't have to worry about this because the following applies...

Quote:

Originally posted by webshot

The relay that came with the car and is faulty is part number 90987-02022 and is white in color.

It is supposed to be replaced by the newer relay part number 90987-02028 and is grey in color.

This relay is found in the fuse box under the hood marked as "MG CLT". "MG CLT" is short for Magnetic Clutch.

My '04 SR5 already has the grey relay.
Good luck guys.

rando · #34 (**permalink**) 05-09-2007, 09:02 PM

The narrative in the following posts describes how I mod'd the magnetic clutch / magnetic clutch sensor circuit to prevent premature failure of the MGCLT relay. In my case, the relay had already failed before I learned of the problem. To test this modification I further destroyed my relay by removing it from its casing. Had the modification been in place earlier, I believe relay failure (and a costly $50+ replacement) could have been avoided.

This modifcation done correctly or not may start your truck on fire, or otherwise cause damage or injury to people, property, or the universe. It worked for me, as described, but I cannot guarantee that it is safe or that it will work for you. By attempting this modification, you agree to proceed at your own risk and accept full liability for your actions and their consequences. The information provided here is for informational purposes only. I do not endorse this modication nor recommend that ANYONE actually perform what is described.

rando · #35 (**permalink**) 05-09-2007, 09:11 PM

These are the locations to connect the diode. The diode is hidden underneath the heat shrink. The red sticker indicates the diode anode.

Anode goes to GND - Pin #4 (center pin) of the Heater relay
Cathode (striped side of diode) goes to the load - Pin #3 of MG CLT relay

rando · #36 (**permalink**) 05-09-2007, 09:22 PM

Here's what it looks like with the relays installed. Hopefully your MG CLT relay doesn't look like mine!

If you're just reading these last two posts, I've confirmed that this eliminates the arcing inside of the relay. If you have the old style relay and it hasn't failed yet (and you're out of warranty), you can save yourself $50+ and install the bypass for < $1.

greasefingers · #37 (**permalink**) 05-09-2007, 09:26 PM

The diode goes across the coil of the relay which one side is ground, so if that pictured diode is across the coil and positioned correctly; then it should work fine to prevent a reverse huge voltage spike when the relay de-energizes.

rando · #38 (**permalink**) 05-09-2007, 09:32 PM

Quote:

Originally posted by greasefingers
The diode goes across the coil of the relay which one side is ground, so if that pictured diode is across the coil and positioned correctly; then it should work fine to prevent a reverse huge voltage spike when the relay de-energizes.

No. In this application, the diode is across the load (i.e. the magnetic clutch solenoid), not the relay coil. Without it, the EMF arcs across the relay switch contacts and dissipates into the battery supply circuit. With the diode, the EMF is redirected to ground.

greasefingers · #39 (**permalink**) 05-09-2007, 09:38 PM

Quote:

Originally posted by rando

More importantly, with the case removed, I can confirm that the diode isn't shunting the kickback (i.e. I can see an arc every time the relay contacts open).

Got ya. If I had read the above more closely then I would have understood.

Nice job Rando!

rando · #40 (**permalink**) 05-09-2007, 09:55 PM

Here's the modified circuit. Per the diagram, you could tap D1 at connector IC4 with an in-line tap to get a cleaner install. IC4 is behind the driver kick panel.

Kmvreter · #41 (**permalink**) 05-09-2007, 10:34 PM

Quote:

Originally posted by rando
you can save yourself $50+ and install the bypass for < $1.

Way to go Rando! I knew you would find the fix for those who need it. Got to love those $1 mods.
Now you need to find a scrap yard and pull a replacement relay for your original. Almost any TOY has that relay.

rando · #42 (**permalink**) 05-09-2007, 10:56 PM

Quote:

Originally posted by Kmvreter
Way to go Rando! I knew you would find the fix for those who need it. Got to love those $1 mods.
Now you need to find a scrap yard and pull a replacement relay for your original. Almost any TOY has that relay.

I take donations!

a77boy · #43 (**permalink**) 05-11-2007, 03:00 AM

Dam Rando you the Freakin' man!! Good job. In the meantime I still need to fart around with my vibrating exhaust which is still driving my crazy at stoplights, Will have to try the diode mod soon.

gizmopt2002 · #44 (**permalink**) 06-26-2007, 11:51 PM

Question. My A/C wasn't working right, it came out cool instead of cold. I added more refrigerant and now it comes out COLD, but it doesn't work at times, I'm thinking about replacing the relay. Any input?

(BTW, rando, are you an electrician?)

rando · #45 (**permalink**) 06-27-2007, 12:33 AM

If your relay fails, you'll get the flashing A/C light and the compressor will shut off (i.e you just get outside or recirculated air depending on your vent settings). If you push the auto button (or the next time you use your A/C), the system may work again, work for only a short while, or not at all.

No, I'm not an electrician by trade. I do have a CS/EE background though.

Quote:

Originally posted by gizmopt2002
Question. My A/C wasn't working right, it came out cool instead of cold. I added more refrigerant and now it comes out COLD, but it doesn't work at times, I'm thinking about replacing the relay. Any input?

(BTW, rando, are you an electrician?)

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