GrantReid

I have a 92 SC400. The heater main relay tested bad with my multimeter. The problem is I know nothing about how to remove and replace it. I checked Ebay, but I can't seem to find the part there or anywhere on line as of yet.

Does anyone know how to remove and replace the heater main relay?

Any suggestions on where to buy it, or if I could get the part number, I can search a place to buy then.

Thanks,

GrantReid

cancel this, i figured it out.

oldManTan

what's the heater main relay? and wat was your problem? i'm just curious because my fan won't work, maybe i can check this on mine.

GrantReid

Heater Main Relay 1992 SC400

I added a pic and circled in red the Heater Main Relay. It is in the Fuse box under the engine hood on the drivers left side right back of the battery.

If your blower won't work, the causes in order of from most likely to least are:
1. Heater main relay circuit
2. Blower motor circuit
3. Water temp. sensor circuit
4. Ignition power circuit

The list goes on. It is an excerpt from the service manual. To check the first one in the list, HMR circuit, you pull the HMR out of the fuse box, get a multimeter and check continuity between the 5 terminals. If you want to know more info let me know and I will explain how to do it in detail.

oldManTan

thanks, i've been looking at the repair manual but couldn't find the location of the relay in it. i'll check it out tomorrow, hopefully this will fix my problem once and for all.

skeet92

iTrader: (1)

Behind the dash under the glove box is a blower relay.

oldManTan

no it's not, there's a power transistor and a resistor there. the relay is exactly where GrantReid showed. waiting for mine to come in, jumped ports 4 and 5 and the air works. this needs to be stickied. can't believe i never checked the damn relay.

chason

It could still be something other than the relay.

Have you applied 12 volts to the relay to see if it clicks?

I'm having an issue with my A/C, and if I take and jump the relay, it turns on and blows cold... relay, right? Nope, the relay is fine. I think it's the actual climate control not sending a signal to the relay.

Nonetheless, if you don't feel like putting 12 volts to the relay when it's outside of the car, just swapping it out is a relatively cheap test.

oldManTan

so your problem is what exactly? my problem was the fan not turning on, everything gets hot and cold just how it should. the only problem i had was the fan not turning on. are you having trouble with it heating up? because that would be a problem with the heater valve.

as for checking the relay i just tested for continuity between 1 and 3 like the manual says and i got none, which is why the relay wasn't working.

EDIT: wrong terminals

chason

No, no, my problem is something else entirely. Two issues, in fact. One is the heater doesn't work (doesn't get hot), it's never worked in the 6 or 7 years I've owned the car. It's probably the heater valve, like you said.

The other issue is that the A/C compressor doesn't kick on (much bigger issue than the heater in Texas lol). When you jump the ports to bypass the relay, the A/C gets ice cold. So you think, oh, bad relay? But the relay isn't bad, it's just not getting the signal to turn on. I'm thinking climate control as it's the next thing up the chain... wish I knew an easy way to test this.

I was just mentioning that jumping the ports doesn't test the relay itself, and you could still potentially have another issue, but it looks like you've got that covered I hope that's all that's wrong with yours... it's always nice when it's an easy fix.

Ali SC3

iTrader: (10)

doesn't get hot is usually the heater valve, or you may be a little low on coolant. try topping it off.

chason

Definitely not coolant... in fact, my SC has never been low on coolant in it's life... all of my other vehicles have required a top off every now and then. Not this one, in almost 100k miles, every time I've ever opened the top there's been fluid right there staring at me.

I did find the $38 dollar heater control valve fix here https://www.clublexus.com/forums/per...t-numbers.html and am going to do that this weekend.

The a/c is going to be a whole other issue. I've checked pressures, bypassed pressure switches... it works great when I manually jump the compressor, but the car doesn't want to kick it off on it's own. Right now I'm leaning toward climate control module or ECU. I'll start a thread on that when I start to dig into it again.

oldManTan

here's an online PDF of the manual, see if you can find anything there. i think i saw something that was like your issue
http://www.driftshop.com.au/SC300%20Manual.pdf

oldManTan

relay came in, another bad one terminals 1 and 3 have no continuity. waiting for another one now. also tomorrow i will check the wire harness in the wheel well, i relocated it, but i'm gonna check it just in case because it was a little chewed. reason for that is because i'm having a hard time getting a voltage reading on the HR terminal which should read 0 volts when fan is on and 12 volts when off. i'm getting none of that so there might be a short in the wire, which would explain the fan turning on randomly sometimes.