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Cooling fans not coming on when temp is reached

Old 08-19-2018, 03:53 PM
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Default Cooling fans not coming on when temp is reached

I can post the wiring diagrams if it is allowed.

I have a 1988 honda accord lxi. I've been trying to troubleshoot the radiator fans not coming on when engine reaches temp. I've tested And replaced The thermo switch For continuity, The one on the thermostat housing, It was faulty so it was replaced As the contacts do not close above temp . According to the wiring diagram in operation, There is a fan timing module under the seat. This thermo sensor sends a signal when the contacts close to the module and tells the fan to turn on if the engine is above a certain temperature when the car turns off. This used to work but just stopped out of the blue.

Now the main fan switch was not badd but i replaced it anyway due to preventative maintenance. I tested this in boiling water and it works. So, When the engine reaches specified temperature the radiator fans do not turn on ( both fans dont as they should) Temperature gauge Is in the hot range so I have to turn the car off before it overheats. A few days ago the condenser fan would automatically turn on for 15 minutes as it should when the car was off but out of the blue just stopped as stated before. At the fan module, There is a blue wire that bridges both relays and that requires a ground through the main thermo switch for the fans to operate. Now key off, If I ground straight to it, Only the condenser fan will run. This is to be expected but not in this circumstance because it's supposed to happen automatically.

Key off, I can Apply voltage to both fans individually and each will come on. The fans do work. With the key on, I can short the contacts On the connector for the main thermo switch And both fans will run. As it should

I can also go to the fuse Box and short the contacts For the main fan relay Key off and the main fan will run. I can also do the same for the condenser fan key off.

Key on, I can short the main fan relay contacts again and both fans will come on. (Provided the connector to the module is connected ) (if not, only main fan will run, to be expected) again, According to the wiring diagram there is a blue wire that comes from the main fan switch connector to the back of the fan timing module. Apparently this needs a grounded input in order to turn the fans on. I probed the blue wire and took it straight to ground and both of the fans turn on.

There is sufficient flow to Main thermo switch on the radiator so the contacts should be closing to give the module the ground input it needs. When temp is there. However the fans do not turn on. The thermostat is installed in the correct orientation. Spring side facing engine, hole orientation up. Bottom of radiator hose get hot.

According to the wiring diagram there are 3 power inputs. Two energized in start or run position. The other hot at all times. I am getting voltage as I should to these wires.

All 5 fuses Are intact and both fan Relays work. I am really at a loss here and have no idea what to do next. I do not want to jumper fans and have them running all the time. I would rather get to the heart of this issue. The car has sufficient coolant and air purged from system. Something to be noted is that the fan timer fuse under the hood and cooling fan fuses were blown, these were replaced. And havent blown again. I question how these fuses blew. Oddly I've rebuilt the engine in this car and did a thorough flush of the system. Replaced thermostat as well.Only 2 times did the fans come on as they should. After that they stopped working, I assume due to blown fuses. also checked the module system board. did not find any burn marks or burnt anything

After nearly a week, I have given up for now and turn to the Honda auto gods for assistance. I surrender my ego to you all.

Please help.
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Old 08-19-2018, 06:03 PM
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Default Re: Cooling fans not coming on when temp is reached

Have you opened that timer box? Good chance it's all green in there. I used to know these cars like the back of my hand, but I'm out of practice now.

I wil​​​​​​I look at a wiring diagram when i get a chance. You may wanna hit up 3geez as well.
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Old 08-19-2018, 06:16 PM
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Default Re: Cooling fans not coming on when temp is reached

i hit up 3geez, but havent gotten much of a response, its been days.

I opened the box up, everything looks new and intact. I'm really tempted to bypass it somehow, but would rather have oem functionality
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