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Old 5th June 2013, 10:49 PM
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300Tdi Air Conditioning Fan will not shut down

Hi All,

I have a 300Tdi Defender which is fitted with Factory AC. I built the land rover from the ground up and sourced a Rest of the World spec loom which means I have a late Td5 style dash and electrics (still no engine ecu though).

The other day I noticed that my AC helper fan on the front of the truck was running all of the time. It will not shut down unless the engine is off. My temeperture gauge reads normal level, and when I squeeze the top rad hose when it's hot the header tank level goes up and down: indicating that the thermostat is open?

Today I replaced both the green and yellow sensors in the engine Ali cast pipe that forms part of the thermostat housing, these I was told can sometimes not function properly trick the fan into being triggered on. Anyway this still hasn't solved the problem. I have a trip down south this weekend from Perth Nd I really don't want to risk overheating my defender (although there aren't any signs of it getting hot).

Anyone got any ideas? Or had a similar problem? I have a 4 core HD radiator fitted if that makes any difference.

Regards

Rob
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Old 6th June 2013, 07:45 AM
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With standard wiring the fan should have nothing to do with the engine temp in a 300TDI.
There are 2 relays in the battery compartment.
One is for the A/C compressor, the other is for the front fan.
Both these relays are controlled by the A/C control box which is located adjacent to the relays.
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Old 6th June 2013, 11:04 AM
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Quote:
Originally Posted by jboot51 View Post
With standard wiring the fan should have nothing todo with the engine temp in a 300TDI.
Quote:
Originally Posted by jboot51 View Post
There are 2 relays in the battery compartment.

One is for the A/C compressor, the other is for the front fan.

Both these relays are controlled by the A/C control box which is locatedadjacent to the relays.
Hi

Thanks for the reply; unfortunately my Defender isn't "standard"so to speak. As I explained it is fitted with a "Rest of The World"or ROW specification loom. I believe Land Rover was building these trucks forexport with the 300Tdi engine until around 2006.

I have taken some pictures of the temperature sensors on the engine which Iknow to be part of the AC system (I bought the kit complete and it came withthe different thermostat housing with the two sensors mounted underneath).

Engine Shot:



Engine shot No. 2:



Td5 Spec interior with Td5 spec underdash AC unit:



The AC "Helper Fan" that is activating when the engine is atnormal operating temperature by the gauge on the dash:



AC Compressor:



I know these probably won’t be much use, but I am still stumped as to whythe fan will not turn off. I went down to the garage this morning and turnedthe ignition on (engine completely cold) and the fan did not start which makesme think it must be temperature dependent (those two sensors).

Thanks in advance.

Rob
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Old 6th June 2013, 11:11 AM
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That thermostat housing is the same as the one on my 300 tdi Disco.

When the fans are operating without the a/c on, if you disconnect those two sensors on the bottom of the housing do the condensor fans cut out ?

If so , it could simply be a faulty sensor

Anyhow doing this could help isolate the symptoms

On my D1, if it overheats to any extent the a/c will cut out and the fans will keep operating

Some vehicles (eg VNs) are set up to allow the fans to continue operating for a short time after switching the ignition off
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Old 6th June 2013, 11:15 AM
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Quote:
Originally Posted by jboot51 View Post
With standard wiring the fan should have nothing to do with the engine temp in a 300TDI.
..........
not quite correct - see above.
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Old 6th June 2013, 11:44 AM
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My 300TDI '97 Disco does this also.
I don't see it causing any damage, and doubt the A/C fan will wear out soon, plus the fans wear out (motor, bearings etc) they are not a hassle to replace and cheap on eBay. I guess when I get time I might get around to trying to solve the issue, but for now.... They run all the time.

Cheers, Adam.
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Old 6th June 2013, 11:50 AM
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Quote:
Originally Posted by 87County View Post
That thermostat housing is the same as the one on my 300 tdi Disco.

When the fans are operating without the a/c on, if you disconnect those two sensors on the bottom of the housing do the condensor fans cut out ?

If so , it could simply be a faulty sensor

Anyhow doing this could help isolate the symptoms

On my D1, if it overheats to any extent the a/c will cut out and the fans will keep operating

Some vehicles (eg VNs) are set up to allow the fans to continue operating for a short time after switching the ignition off

Thanks for the reply. I replaced both of the sensors with new items lastnight, no effect. As soon as the truck is up to temperature the condensercooling fan kicks in. I will try disconnecting the sensors to see if that has any effect when the engine is fully warmed and the fan is on.


*Edit* temp ranges

The Part no. Green PRC3359 and Yellow PRC3505A

I found the below temperatures on a google search (I do not know what the f & L stand for though).

I think the yellow controls the fan and the green shuts the AC compressor down.

Yellow PRC3505 f100/94c
Green PRC3359 L115/109c

Rob
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Old 6th June 2013, 01:07 PM
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Swap the yellow and green plugs over. I bet that solves the problem.
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Old 6th June 2013, 01:09 PM
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They are both temp senders, but slightly different. Both will make your temp gauge appear to work correctly, but only 1 will turn your fans on at the correct temp.

Thus, swap the wires/plugs....
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Old 6th June 2013, 01:18 PM
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Quote:
Originally Posted by Judo View Post
They are both temp senders, but slightly different. Both will make your temp gauge appear to work correctly, but only 1 will turn your fans on at the correct temp.

Thus, swap the wires/plugs....
Judo,

With due respect I dont understand why this has started happening, I havent changed the wires over and no one else works on my Defender. I would much prefer to get to the bottom of why it appears that my engine is overheating.

PRC 3359 (Green plug) is NC (normally closed) and is designed as a circuit breaker in conjunction with the other switch i.e if the engine is overworked and over heating it switches the air con off completely.

PRC 3505(Yellow plug) is NO (normally open) switch and switches the fan on to increase the cooling once the coolent temp reaches 94 degrees C, but is overridden by PRC3359 at an even higher temperatures so the engine does not have to cool the AC condenser as well.

My theromostat should be opening at 88degrees, which would indicate that the engine is overheating (going by when the AC fan is switching on).

Regards

Rob
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