engine fan always on high ....even engine off key on

[Ertech]

hi guys .
high fan always on oven engine off key on . I know A/c red switch has nothing to do with it but I disconnected it and I also disconnected the 2 blues temp switches , climate control also off . what to do next ?

it might be related to this ongoing problem

E

Thread 'Engine fan clicks on off ....'

Jun 1, 2020

Hi guys
The engine fan turns on and off quickly a few times
And I can hear a relay clicking in back of the headlight switch .
This happens when I turn off the climate control
Thanks

• Ertech
• Replies: 18
• Forum: Heating and Cooling (Interior HVAC systems)

• 

thanks

 

[Ertech]

My car has the brown relay. I have a spare green one. I tried replacing it, and the fan is still on.

 

[gsxr]

It's the 2-pin sensor on the intake manifold which provides the signal for the aux fan high speed, and IIRC it's the HVAC pushbutton that actually controls it.

2-pin sensor --> HVAC pushbutton unit --> Relay --> Fans

Check to see if your 2-pin sensor is in spec, and if the harness is good, with a tight connection.

The relay isn't the problem, if it failed, the fans would never turn on. Something upstream is triggering the relay.

 

[Ertech]

if I disconnect the 2 pin sensor should the fans stop?
something has always been weird with Hvac , when I stop on the HVAC the fans cycle on off on off for like 5 sec , now when I play with the buttons on off a few times they stop .
I posted a while ago about this problem.
can I repair the HVAC?
thanks

 

[emerydc8]

Disconnecting the 2-pin sensor on the manifold should cause the fans to activate in high-speed mode. If you’re getting the fans to turn off and on with the push buttons I would consider finding a used unit for troubleshooting.

 

[gsxr]

Yep - sounds like a faulty HVAC PBU. Never heard of this particular failure mode. Swap in a good used one.

 

[Ertech]

a little update .
1- replace hvac control with a good used one
2- removed the connector to the 2 pin sensor and shorted them
3- disconnected a/c red switch , then shorted them
fan still on high even with engine off key on .
kinda lost lol

 

[gsxr]

2-pin sensor is not a switch, is a resistive type sensor that varies resistance signal to tell the HVAC system what the coolant temp is. Shorting the sockets will tell the system that coolant temp is high, but zero ohms is out of range of the sensor and I don't know what the system does with that "wrong" signal. Usually with the fans off and engine running, if you just unplug the connector from the sensor, the fans turn on high.

A/C red switch, when shorted, will turn the fans on LOW speed. But if the fans are already on high speed, this will do nothing.

You could have something wrong with the wiring causing the relay to be triggered when the HVAC system is not calling for it.

 

[Ertech]

Should I just order a temperature switch and see how that goes?

 

[gsxr]

Should I just order a temperature switch and see how that goes?

Nope, test the one you have first, using the chart in my previous post. I doubt the sensor is bad.

 

[emerydc8]

I didn’t see this information on your profile, but what year is your vehicle? The later (face-lifted?) cars have two fan ice-cube relays in the relay box—one for low-speed and one for high-speed.

 

[Ertech]

Car is a 1994

 

[Ertech]

I just measured the temp sensor it around 15 celsius and reading is 3.4 k ohm's

 

[gsxr]

I just measured the temp sensor it around 15 celsius and reading is 3.4 k ohm's

Hmmm. That is out of spec. You could try replacing it and see what happens. Compare readings on the old vs new sensor at the same (room) temperature.

 

[Ertech]

The plot thickens this morning it’s about 20°C and my sensor checked out at 6.4 k ohms
With the engine off key on, I played with the controls of the Hvac a few times until the fan stopped. Then I went straight to the engine disconnected. The temperature sensor and the fans did not come on. Should I buy a used Hvac in case my second one was not good.? i’m reading conflicting opinions. Does my car have two
relays can one be stuck?

 

[emerydc8]

Does my car have two relays can one be stuck?

If it’s a 94i think you have two ice-cube relays—one for low-speed fans and one for high-speed. I don’t recall which is which but I would take a look at the relay box and see. Both should have 30 Amp fuses on top.

 

[Ertech]

Great swapped those and problem still there ?

 

[gsxr]

Great swapped those and problem still there ?

That means the relays are fine.

 

[Ertech]

can I be confusing low and high speed?
I was able to make them stop while playing with the ignition . I disconnected the temp sensor and the fans do not kick in . ,I bridges the red sensor and the fans work .
sorry for being confusion

 

[gsxr]

Bridging the red sensor will turn the fans on low speed. This is fairly quiet.

High speed fans are LOUD. There is a big difference between low and high speed.

If you cannot tell a difference, check if someone bypassed the auxiliary fan resistor located behind the driver headlight, below the ASR unit.