I'm still learning so would love some advice please re: car ecu not powering ac fan

Thread Starter

MedicareEMR

Joined Nov 13, 2022
7
Hi everyone,

So let me start off by saying that my ADHD and OCD cause me to want to know so I learn new skills often. Let me break down the basics of how I got to this point, 3 motors later, thanks to the mechanic and his slack lazy staff who don't take pride in their work, I ended up with an overheating car, thrice. To cut a very long story short, since then I had to drive with the aircon on in order for the fan to engage, that was fine as we going into summer here in SA. Then after one of the aircon pipes broke, a colleague unplugged the ac condenser to stop it sucking dust in as we were shooting on a farm for a few weeks, I was the snake wrangler on set and the dusty roads were a recipe for disaster. But unplugging it resulted in the fan not working at all and when it was plugged back in, it did not want to come on again, hence the connecting up directly until I could take the time to troubleshoot.

So after testing a few relays in the fuse box and having no luck finding the issue, I had to go to the next step, as the fan was not getting triggered by ECU and the fuse box wasn't giving the fan a power source. So I have removed the fuse box and have been testing the components to see if there was anything.

So the following relays are present :
3 x Nikko YHT KRTB1-225L 12vVDC (Horn, AC & Park)
3 x Fujitsu 53ND12-Y-05 1037F B8 ( Fan Lo , HDLP Lo & Hi)
I desoldered the Fan Lo, Horn & AC to test out of the circuit and they all repeatedly triggered when given 12vdc, my horn was working before so swapped it out with an AC relay just in case, these were returned to the board.
Then each of the SMD relays have a 102 resistor before powering the relay, with no relay in the circuit the resistors came up ..OL on the screen, but here is the thing I am puzzling with, once relays were in place the 102 gave readings varying from 185.5-202, is this in normal parameters, I'm almost sure I checked them before touching the board and were in the 202-204 region. I have attached some pics.

So I remembered a while back one of my LED emergency lights also had a bunch of 102's and I had purchased replacements from a spares place and they didn't have 102's, so he gave me 103's as a replacement to use, my question is can these be used in place of the 102's safely for the car considering its not an emergency light, because I need to get my car back on the road asap? Look forward to hearing your advice.

Thank youy
 

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A couple thoughts...

Chances are the resistors are actually capacitors. That would explain why they show OL with the relay out... you actually end up measuring the relay coil instead with the relay installed. The numbers sound about right.

A 102 resistor would be 1000 ohms and a 103 would be 10000 ohms. Either way a relay would not work with that much resistance in an automotive circuit unless you have some strange solid state relay (Never used in NA or Europe as far as I know, but trying to keep an open mind)

A 102 capacitor would be 1 nF and 103 capacitor would be 10 nF. Depending on what they actually are used for it is possible they may be interchanged, but the chances of that actually being the problem is very slim.

How exactly did you test the relays? I have had on several occasions where everything measured and looked right on my meter only to find the internal contacts were actually pitted and worn enough that it would not provide enough current to make whatever it is powering work. An engine fan will draw a fair amount of current!!

I see a fan low, but not a fan high. Is your fan a two speed fan? If so the reason it may work with A/C is the A/C is using the high speed circuit. If that is the case then the fan itself is probably no good.

If not a two speed fan then my next guess would be a broken wire between the ECU and the fan relay, or a faulty temperature switch or broken wire. Some engines use a dedicated temperature switch on the engine instead of being run of the ECU... it was more common in older vehicles, but it's still a possibility today.

Unfortunately your circuit list images are not readable so I couldn't look for clues there.

What kind of vehicle you working on?
 

Thread Starter

MedicareEMR

Joined Nov 13, 2022
7
Hey, so I am working on a 2011 chev spark 1.2

So I figured out that the three smaller relays 102's were measuring the 188 mark and the 3 bigger ones were 200. In testing the relays, I applied 12v to the power pin, making them click repeatedly. So in my mind they were still working lol. Anyways returned them to the board, reassembled everything and started the car and let it run and almost let it over heat, but caught it time, I bypassed the the fuse box and ran the fan to cool the motor. Yesterday I wasn't getting power, today I was, but it wasn't 12v.

I have a OBD2 connector attached permanently to watch the temp as the car doesn't have a display. This morning I got excited as I was getting power, but not 12v, at higher temp it gave just over 9v and dropped with the temp slowly to 5v. this was the output at the plug that powers the fan. now its dead again, so I am going to put in a switch inside the car running straight of the battery. My knowledge as it is is not enough for me to figure out to bypass it on the fuse box. There is also no power to the 10amp AC fuse and the 20amp lo fan fuse. The PCB board is in the plastic housing with the wiring harnesses connected to the bottom and fuses/normal relays plugging in on top with fuses. the 6 relays you see are on the inside and are depicted by the blocks with dotted lines as in the pic. I have added the pics again after clearing them up. I have replaced all three temps sensors recently in an attempt to get the fan running normally.

Shot for responding, appreciate the input
 

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In testing the relays, I applied 12v to the power pin, making them click repeatedly. So in my mind they were still working lol.
In theory you are right, and 90% of the time you would be right. There's the other 10% of the time when things want to be a pain and you finally find it after you replace the relay.
I think you mentioned swapping around relays already... I didn't see it until after I posted last time. It also looks like you have the type of relays that are possible to be installed backwards. I don't think this is the problem due to something else further down your post, but beware it is possible. Why they are designed this way I have no clue. If it weren't for that I could describe a few ways to test wiring, but without being there myself I don't want to tell you the wrong pin and cause major damage.

This morning I got excited as I was getting power, but not 12v, at higher temp it gave just over 9v and dropped with the temp slowly to 5v. this was the output at the plug that powers the fan.
That is normally a sign of either corrosion, a broken wire, or a worn relays. The fact that it changes with temperature would make me look for areas that are affected by temperature and not so much relays. Maybe as the wire warms up it moves, expands, the insulation gets softer, or whatever and changes things.

There is also no power to the 10amp AC fuse and the 20amp lo fan fuse
There are times the fuse comes after the relay and won't have power unless the relay is on. I can't say for sure if this is your case, but I would suspect this is what is happening.

I have replaced all three temps sensors recently in an attempt to get the fan running normally.
So much for the easy fix.

I wish I had a better idea, but without wiring diagrams or being there myself my only suggestion is start at the fan and cut the harness open until you find a problem. Your boards look good and it seems like you are getting something at the fan now and again so the problem is most likely between your relay and the fan itself.
 
PS Fan works when I bridge pin 30 & 87, wiring good
That was something I wanted to suggest, but wasn't sure if you were up to it or not, and with those relays if you don't have the relay orientation right you'll short the coil circuit trying to do it if I remember it right. I always have to dig out my diagram and poke around to figure out what is what when working with those ones.
 
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Hey, so I am working on a 2011 chev spark 1.2

So I figured out that the three smaller relays 102's were measuring the 188 mark and the 3 bigger ones were 200. In testing the relays, I applied 12v to the power pin, making them click repeatedly. So in my mind they were still working lol. Anyways returned them to the board, reassembled everything and started the car and let it run and almost let it over heat, but caught it time, I bypassed the the fuse box and ran the fan to cool the motor. Yesterday I wasn't getting power, today I was, but it wasn't 12v.

I have a OBD2 connector attached permanently to watch the temp as the car doesn't have a display. This morning I got excited as I was getting power, but not 12v, at higher temp it gave just over 9v and dropped with the temp slowly to 5v. this was the output at the plug that powers the fan. now its dead again, so I am going to put in a switch inside the car running straight of the battery. My knowledge as it is is not enough for me to figure out to bypass it on the fuse box. There is also no power to the 10amp AC fuse and the 20amp lo fan fuse. The PCB board is in the plastic housing with the wiring harnesses connected to the bottom and fuses/normal relays plugging in on top with fuses. the 6 relays you see are on the inside and are depicted by the blocks with dotted lines as in the pic. I have added the pics again after clearing them up. I have replaced all three temps sensors recently in an attempt to get the fan running normally.

Shot for responding, appreciate the input
The 9v and 5v readings sound like you are measuring the voltage from a thermistor which is a resistor that has a voltage drop across it that varies with temperature
 

Thread Starter

MedicareEMR

Joined Nov 13, 2022
7
The 9v and 5v readings sound like you are measuring the voltage from a thermistor which is a resistor that has a voltage drop across it that varies with temperature
The measurement was taken from the + & - cables going into the fan whilst the fan was running. I have since bypassed the fuse box with a direct connection to the fan with a switch and relay circuit in the interim so I can switch it on whilst driving. At least my car won't overheat now in summer. My reasoning is that on one of the spark forums its was said that the fan wont run if the aircon doesn't come on, which is currently my problem, I had to get a pipe welded the other day to fix the system so it can be regassed.

if I get it regassed and the normal fan still doesn't engage or trigger when temp gets high, could I connect both the fuse box connection and my manual switch to the positive of the fan as a fail safe? Just incase the aircon doesn't work ?
 
My reasoning is that on one of the spark forums its was said that the fan wont run if the aircon doesn't come on,
That sounds a bit fishy, but I can't say one way or the other. The whole A/C part of it had me wondering in the beginning, but I figured the fan should work without it anyways so I didn't say anything. Normally the compressor should not work without any refrigerant in the system. The pressure switches are usually designed only to turn on above 20 or 30 psi. The reason being the lubricant for the system is suspended in the refrigerant and without it the compressor will overheat and seize up.

Is there by chance a second pressure switch in the A/C system? I know with what I work with some older units had a separate switch that would turn on the fan when the line pressure hit around 300 psi and it would stay on until the compressor stayed off for a certain amount of time. I was wondering if there was a switch that would switch between the ECU fan signal and turning the fan on and off as needed for the A/C
 

Thread Starter

MedicareEMR

Joined Nov 13, 2022
7
The Aircon is a separate issue which resulted after the pipe snapped off just above the bolt where it attaches to the compressor. I have downloaded the manual of the vehicle and will have a look to see if there is a second switch, I am going to have the aircon gassed today, Must just top up the compressor oil as some came out when I took the compressor off to make sure it was still functioning, which it was still is.

The fan and the car overheating was the first original issue. The fan stopped engaging when it should work due to the temperature, according to the spark forum, the operating temp is 85-102 degrees celsius. And come to think of it, it hadn't been working for some time, but the car was still running fine. I'm on my way to an eye appointment, then will have it gassed and will reconnect the fan via the fuse box, but am going to keep the manual overide connected as well, not taking any chances again.

Thanks for the thoughts, will let you know re switch
 

Thread Starter

MedicareEMR

Joined Nov 13, 2022
7
Ok, at least its some good news, aircon is working and no leaks. has only 1 switch. now to reconnect it to the system and see if any issues arise and performs as per requirements.

Thanks to everyone's input thus far, much appreciated. I have a few electronic projects I am busy with and look forward to picking some more brains lol
 
You are welcome. I tried to look around online for more information so as to not just guess at what I thought was happening, but had no luck. The manual will help you more in the end than my guesses can.
 
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