Testing Fan Resistor

tulit

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110
I spent some time pulling apart the cooling system on my car today.
I thought one area that may be helpful to explain is testing the fan resistor is still measuring within spec which is a common failure point.

 

Oishi

Member
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825
Thanks tulit for posting this, I had forgotten that the website was there and had to rediscover that info by experiment. As a side note, as I was wrestling with removing mine, I noticed that there are 2 types of rad. shrouds. Early type is metal and one piece, later type plastic and two pieces with the fans built in. The later type has a second place for a resistor at the top. Has anyone used that location for their resistor?
 
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lambertius

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341
I didn't even know this was a thing, but it sounds like mine is stuck open. I'll look into it! Where is that resistor located?

As a side note, the AC compressor doesn't trigger the fans which is normal operation in any other car using TX valve. I was going to look at wiring a relay to trigger one of the radiator fans whenever the compressor engages. It should prevent the pressure spiking and overall improve the efficiency of the AC system. While you're playing around with the radiator and wiring, it might something worth exploring for yourself.
 

tulit

Member
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110
It’s near the bottom of the fan shroud in the middle.

Mine calls for speed 1 fan immediately as soon as the AC is turned on. I think this is standard to get air flowing across the condenser.


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tulit

Member
Messages
110
BTW- The Launch has the ability to test both speed fans. I did however need to go into the Granturismo ME7 menu to get it (the QP and GS menus only allow you to engage the one speed oddly enough). I'd start there and see if your first speed is even working.
 

Zep

Moderator
Messages
9,110
The fan operation for the A/C system is governed by the pressure switch which located at the outlet of the drier which functions as a loss of charge, high pressure safety switch and a fan speed switch. The low pressure switch disables the system below 2.85 bar to prevent damage from a loss of refrigerant. The low fan speed is engaged at 15 bar and the high fan speed at 20 bar. Finally there is a high pressure cut out at 28 bar. These are designed to keep the condensing pressure in the appropriate range to allow heat transfer and produce a suitable amount of sub cooling to feed the evaporator and TXV as well as preventing over condensing which causing a reduction in the volume flow of refrigerant, reducing efficiency. To wire the fans in any other way would not be sensible, particularly in cooler climates.
 

lambertius

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341
oooh, that is an interesting discovery - what prompted you to try that? I'm 99% sure my radiator fans only operate at one speed but I will definitely try and test it - does the engine need to be running or just the ignition on?

Just found the this is the service manual for the AC. Normally I would expect to see one fan operate independently of the other and just turn on whenever the compressor engages, but this description implies that it is triggered by the system pressure and should then lag the engagement of the compressor, which is what I see. I've never seen the fans engage individually though, I may have to try running the ac on a cold day immediately at startup while the engine is still cold, before it calls the radiator fans.

72690
 

lambertius

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341
Just had a penny drop - when I fixed the AC system and we were testing it, we thought it was strange that the fans would only engage once the system hit 20 bar. I'm going to guess that it couldn't engage the low speed setting by how it is wired up which is why we were seeing the pressure spike.

That should also help with the AC system.
 

tulit

Member
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110
You can test the fans without the engine running. Just turn the key all the way. The program should turn the fan on for about 5 seconds when you select it and it's pretty easy to hear the difference between low/high. From your description, it sounds like maybe your 1st speed resistor is shot. Should be okay as well to jumper the two plugs going into it (effectively making low speed also a high speed setting) to isolate whether its a fuse or a relay (each speed has their own of these as well).

Out of curiosity, what service manual is that AC excerpt from? I dont seem to have that one. Thanks!
 

lambertius

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I'll email it to you, its some service training slides - not very detailed, but it did help me when I was chasing down some other faults early on just because I could look up the system pressures.
 

tulit

Member
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110
oooh, that is an interesting discovery - what prompted you to try that?

There's a lot of discrepancy between "features" on various vehicles even though they all use the same systems. If I can't find something, or something doesn't seem to be working right I'll usually go through the various Ferrari/Maserati options (GT, QP, 360, 8C, F430, etc). One of them usually works :D For example, the GS doesn't seem to have all the long term fuel trims either, but all of them are available on the GT.
 

lambertius

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Well that is interesting, I will definitely have a play.

I hadn't looked at it much further than playing with the transmission. My engine runs well, so everything I had looked at had been with the transmissions. I had no idea about the resistor and so just hadn't thought of it at all. I'll test it on my car in the morning and see if it confirms what I now know!
 

lambertius

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341
I messaged a few other owners in Australia, and none of them have a working resistor regardless of mileage. One the cars I've driven, none of them had the fans engage at the lower speed that I can recall.

Does anyone know if there is a more resilient part available? Sounds like it is another cheap part/engineering level issue...
 

tulit

Member
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110
There's lots of options, but they all use the same concrete wire wound resistor.

Part of me is contemplating to just cut the resistor out (e.g. connect the two leads permanently) and let "low" speed simply be "high" speed. Other than the fans possibly being a bit louder than they need to be, it would get rid of a common failure point.
 

lambertius

Banned
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341
There's lots of options, but they all use the same concrete wire wound resistor.

Part of me is contemplating to just cut the resistor out (e.g. connect the two leads permanently) and let "low" speed simply be "high" speed. Other than the fans possibly being a bit louder than they need to be, it would get rid of a common failure point.

That actually sounds like the best solution. I can't hear the fans running at all from inside the car, so I can't see what practical difference it would make other than when its idling and you're outside the car.

I wish I had thought of that before getting the resistor!

I'll get some high gauge wire and blade connectors and bypass it when I get home. IMO its better that it kicks on earlier louder, than late. If I had to take a guess, I would say all the Australian cars are blowing the thermal fuse that you mention. All of these cars would've been out on days 40+ multiple times.
 

Phil maserati

New Member
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7
BTW- The Launch has the ability to test both speed fans. I did however need to go into the Granturismo ME7 menu to get it (the QP and GS menus only allow you to engage the one speed oddly enough). I'd start there and see if your first speed is even working.
Hi Tulit which Launch do you have? I have the 8901 but it does cove some basic stuff, but it looks like you doe more. Many thanks Phil