Heater Relay low voltage coil input?

[Isaac1]

The air conditioning / heater blower stopped working on my 2007 Yaris 3 door hatchback last week. At first I assumed it was the blower motor or the resistor (resistor looked nasty and corroded when I removed / replaced it. Afterward there was still no power getting to the blow so I checked the various fuses, and all of them seem to be good. After much digging I have found the blue heater blower relay in the interior fuse panel is only getting about 5.5 volts DC to the coil input, which is not enough to trip the relay, All other voltages seem to be good, I have also checked the ignition relay, and have pulled the harness from the ignition switch under the steering wheel.

If I manually jumper power to the green ign wire at the ignition switch, I can hear a pair of relays clicking with a slight delay between them, the first is the pink ignition relay in the interior fuse panel by the drivers left leg, then there is second relay that sounds like it is up under the center dash area somewhere. When I remove power from the green ignition wire there the pink relay clicks off first, then about a second later the mystery one clicks, it is at this point that the 5.5VDC I am getting to the input coil side of the Heater relay clicks off to 0 VDC. I am assuming my problem is bad contacts on this second mystery relay, can anyone help me find it?

Looking online it appears there are no relays on the Yaris Air Conditioner amplifier board, though I plan to check that one tomorrow, as I ran out of day light today before getting to it.

Thanks

p.s. bypassing the heater relay lets the blower work.

[sh0rtlife]

the ac amp board as you called it is bolted to the BOTTOM of he heater box directly to the right of the gas pedal up under the heater box....and im not aware of it having any relays..tho it could as its certainly large enough

are you sure the blower switch isnt the fault?..one can be used from most scions and half a dozen other toyotas, in fact the "knobs" can be swapped if the unit you find to test with solves the issue....theres 2 types a "deep" and a "shallow" with the deep being the newwest version on the newwer xb's...sorry i dont have part numbers...only reason i know about the slight change was i swapped my knobs out for black knurreled units but the knobs i got were for the deep units and had to swap the whole units

back to the relays...double check the engine bay relays as i know the heater uses one of those directly..but i dont remember which one...and it also uses one internaly at the otehr fuse box..beyond that ive skinned out the entire heater/ac harness to do an ac retro fit so i kinda know first hand where every wire goes...of course it was a waste of time as i later found out my 07 was pre-wired so the ac swap was plug n play

unless you have a sedan...and they did something weird..there are no relays or anything outside of the fuse boxes

[Isaac1]

Thanks for the replies, I am 100% sure that the fan switch works, as the fan now blows if I jumper past the heater relay at the under dash fuse box, the relay is just not getting enough voltage / current to turn on.

p.s. I have checked the under hood relay on the right side, it tested marginal (.3 ohms across the contacts when jumpered) so I replaced it, no change at the heater relay, still getting about 5.5VDC when ignition is on or when pin is jumpered on the harness that plugs into the ignition switch.

I am lost now on what powers the heater relay in the fuse box and why the voltage is low I tried unplugging the Air conditioner amplifier and it has no effect on voltage at the heater relay.

[sh0rtlife]

heres the thing it may not be a voltage issue in fact these relays are ment to work on low volt/amp in fact it shouldnt need a full 12v to function..
take note of how small the wiring is...swap out the relay and you might just solve it..heck swap it with any of the identical relays in the car and see if it fixes it

[Isaac1]

I already swapped it out, no luck, tracing more it looks like the voltage drop is occurring inside the fuse box, weather permitting tomorrow I will try to rig a bypass wire for the supply side power for the relay vs pulling the fuse box out of the car.

[sh0rtlife]

you might have a "semi bad" fuse /connection if thats the case....my alfa's LOVE to pull that trick and i have to clean the contacts in the fuse box and fuses to fix it

on the lil spade fuses our yaris use, you can get a thin fingernail file and cut it to width

[Isaac1]

It is worth a try