Fans work, but dont kick in-help.
Discussion
Following on from the MOT fail thread, I wanted to check my fans.
Its a 1999 996
They kick in when the AC is turned on, but not when the car gets hot. It got to 101c (214F ish)but didn't kick in. I pressed the AC on, they came on-but turned off when the AC was turned off.
Now of course I could just leave the AC, but that's not the point!
Any ideas?
Thanks
Its a 1999 996
They kick in when the AC is turned on, but not when the car gets hot. It got to 101c (214F ish)but didn't kick in. I pressed the AC on, they came on-but turned off when the AC was turned off.
Now of course I could just leave the AC, but that's not the point!
Any ideas?
Thanks
Did you try jumping the power terminals on the low speed fan relays to check this turns the low speed fans on?
If it doesn't then you need to replace the resistors for the low speed circuit.
The high speed is just a straight 12v feed to the fan but low speed goes through a chunky resistor to reduce voltage (and thus speed). This fails with age and the voltage is no longer passed to the fan preventing it turning on.
If you can activate high and low speeds from the relay panel then you need to start looking elsewhere.
If it doesn't then you need to replace the resistors for the low speed circuit.
The high speed is just a straight 12v feed to the fan but low speed goes through a chunky resistor to reduce voltage (and thus speed). This fails with age and the voltage is no longer passed to the fan preventing it turning on.
If you can activate high and low speeds from the relay panel then you need to start looking elsewhere.
fioran0 said:
Did you try jumping the power terminals on the low speed fan relays to check this turns the low speed fans on?
If it doesn't then you need to replace the resistors for the low speed circuit.
The high speed is just a straight 12v feed to the fan but low speed goes through a chunky resistor to reduce voltage (and thus speed). This fails with age and the voltage is no longer passed to the fan preventing it turning on.
If you can activate high and low speeds from the relay panel then you need to start looking elsewhere.
Thanks.If it doesn't then you need to replace the resistors for the low speed circuit.
The high speed is just a straight 12v feed to the fan but low speed goes through a chunky resistor to reduce voltage (and thus speed). This fails with age and the voltage is no longer passed to the fan preventing it turning on.
If you can activate high and low speeds from the relay panel then you need to start looking elsewhere.
Can you tell me how to get the high speed to fire up?
same, pull the relay for the high speed circuits and jump the switched terminals on it. there are 4 relays for the fans. low speed left, high speed left, low speed right, high speed right.
just pull the relay, get a link of wire stripped at both ends and jump across the two terminals for the switched side (not the coil) with ignition on. the fans should kick on at the appropriate speed and side.
if high speed works fine and low speed does nothing you need new resistors.
just pull the relay, get a link of wire stripped at both ends and jump across the two terminals for the switched side (not the coil) with ignition on. the fans should kick on at the appropriate speed and side.
if high speed works fine and low speed does nothing you need new resistors.
fioran0 said:
same, pull the relay for the high speed circuits and jump the switched terminals on it. there are 4 relays for the fans. low speed left, high speed left, low speed right, high speed right.
just pull the relay, get a link of wire stripped at both ends and jump across the two terminals for the switched side (not the coil) with ignition on. the fans should kick on at the appropriate speed and side.
if high speed works fine and low speed does nothing you need new resistors.
I really appreciate the help, but I have to admit I do not know what you mean by "the two terminals for the switched side (not the coil)".....I am a bit of a novice, but AM capable of stripping wires to do this, just not sure where to stick them lol.just pull the relay, get a link of wire stripped at both ends and jump across the two terminals for the switched side (not the coil) with ignition on. the fans should kick on at the appropriate speed and side.
if high speed works fine and low speed does nothing you need new resistors.
are you capable of following a basic circuit diagram?
if so, when you pull the relay out there will be a diagram on the side showing how its configured. 4 terminals, all numbered (30,85,86,87 probably) and looking something like this picture on the right:
in this photo, terminals 85 and 86 control the coil, this is what turns the relay on and off. terminals 30 and 87 are the switched side and this is the circuit that is turned on and off by the relay.
you want to jump across the two terminals that are for the circuit being switched. in this case 30 and 87. it will likely be the same two numbers on your relay but always best to check.
look at the relay body by the blade connectors so see what blades correspond to these terminals as per the photo on the left, work out where they are on the relay board side and you are in business.
if so, when you pull the relay out there will be a diagram on the side showing how its configured. 4 terminals, all numbered (30,85,86,87 probably) and looking something like this picture on the right:
in this photo, terminals 85 and 86 control the coil, this is what turns the relay on and off. terminals 30 and 87 are the switched side and this is the circuit that is turned on and off by the relay.
you want to jump across the two terminals that are for the circuit being switched. in this case 30 and 87. it will likely be the same two numbers on your relay but always best to check.
look at the relay body by the blade connectors so see what blades correspond to these terminals as per the photo on the left, work out where they are on the relay board side and you are in business.
Edited by fioran0 on Saturday 20th October 17:08
OK, this is where I am up to.
Engine on, AC on, fans BOTH work.
I removed both the low-speed and high-speed relays for one side. I cut and strip a piece of wire about 1.5" long.
I inserted one bare end in the output socket (pin 87, center bottom horizontal slot) for the low speed relay and the other end in the output socket for the high speed relay. When I turned the ignition on, the left side fan blew fast, both with the AC on and off.
I put that all back to nomal and did the same for the right side fan. This time there was no fan with the AC off, but fast fan with the AC on.
What I do know is that both fans work at slow and fast speed. I guess what I dont know is if the fans come on when hot enough.
Engine on, AC on, fans BOTH work.
I removed both the low-speed and high-speed relays for one side. I cut and strip a piece of wire about 1.5" long.
I inserted one bare end in the output socket (pin 87, center bottom horizontal slot) for the low speed relay and the other end in the output socket for the high speed relay. When I turned the ignition on, the left side fan blew fast, both with the AC on and off.
I put that all back to nomal and did the same for the right side fan. This time there was no fan with the AC off, but fast fan with the AC on.
What I do know is that both fans work at slow and fast speed. I guess what I dont know is if the fans come on when hot enough.
dont just jump across between the low and high side!
jump across the switched terminals on the low speed fan on one side only (30 and 87 in example above) then do the same for the high speed fan on that side. repeat for opposite side of the car for both low and high speed. you should have two speeds, each side.
what you are doing by doing this is manually replicating what would happen when each relay was triggered. terminals 30 and 87 close and send 12v to the fan circuit.
AC on or off is irrelevant for this test. If the relay is out the car can't control anything. You are sending 12v to the fan circuit manually.
it may be best you just take it to someone to look at it. its only going to get more complicated going forwards to diagnose/fix and it seems a bit beyond your level at the moment
jump across the switched terminals on the low speed fan on one side only (30 and 87 in example above) then do the same for the high speed fan on that side. repeat for opposite side of the car for both low and high speed. you should have two speeds, each side.
what you are doing by doing this is manually replicating what would happen when each relay was triggered. terminals 30 and 87 close and send 12v to the fan circuit.
AC on or off is irrelevant for this test. If the relay is out the car can't control anything. You are sending 12v to the fan circuit manually.
it may be best you just take it to someone to look at it. its only going to get more complicated going forwards to diagnose/fix and it seems a bit beyond your level at the moment
Edited by fioran0 on Saturday 20th October 17:28
Just done it! Perfect instructions!!
It seems that the left hand side front is not coming on low. All the other fired up just as you said.
Does that mean a resistor is broken?
By the way, thanks for the help. I am not useless at doing stuff normally, just not au fait with the terminology.
The car has never overheated, but I have just never noticed the high speed fans kicking in-on my last one, it was like a sand storm when they did.
It seems that the left hand side front is not coming on low. All the other fired up just as you said.
Does that mean a resistor is broken?
By the way, thanks for the help. I am not useless at doing stuff normally, just not au fait with the terminology.
The car has never overheated, but I have just never noticed the high speed fans kicking in-on my last one, it was like a sand storm when they did.
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