Discovery II Diesel Front Mounted Air Con Fan Problem

Hi,

Would appreciate any advice on this problem I have.

Aircon gassed up, pressures getting very high and front mounted fan not cutting in.

Ruled out pressure switch, as unplugged this and compressor cuts out.

Relay has the 12v feed from the battery, and the main engine relay.. so 2x 12v feeds.

Wire out from relay to cooling fan has low resistance, so not a bad wire.

When bridging the relay, the fan runs perfectly fine so its not seized and working... also checked fan fuse which is good, wouldn't run fan if was bad and when fan is running pressures come down to normal pressures for the ambient temperatures.

So problem seems to be that the ECU is not switching on the fan or the wire is bad, I've managed to find out the wire is a Green / White wire.

Are there any known problems relating to this wire or the ECU not switching the negative wire to activate the fan?

I found this on another forum,

For A/C system:
⇒ On When vehicle speed is 50 mph (80 km/h) or less and ambient
temperature is 28 °C (82 °F) or more
⇒ Off When vehicle speed increases to (62.5 mph (100 km/h) or ambient
temperature decreases to 25 °C (77 °F)

Surely that cant be right? the pressures kept going up and up without that fan running, admittedly it didn't reach 28 degrees today... but ive never come across another vehicle where the Aircon fan doesn't activate. Although I can understand it if the viscous fan is generating enough airflow its not always required.

Guess I can test it, by removing the sensor and placing it against the condenser which gets certainly above 30 degrees,

Or is the problem with the viscous fan not generating enough airflow?


Thanks

Hi, first of all what pressures are you speaking about, you keep saying

...when fan is running pressures come down to normal pressures for the ambient temperatures.

Click to expand...

so explain that^^^

the pressures kept going up and up without that fan running,

Click to expand...

or that^^^

that fan relay will get the earth path from the engine ECU only if those conditions are met:
1. 28*C ambient temp, corroborated with aircon on and set to lower than ambient
2. the engine coolant temp gets to 110*C

it has nothing to do with any pressure, also the ext temp above 28*C is irrelevant as long as the aircon is not on and set to smaller temp request than the external temp

so set the aircon on AUTO to let's say 20*C and use a hair drier on the ambient temp sensor(behind the grill) and see if it works then

Hi,

I should of mentioned I am an automotive air conditioning technician.

By pressures I'm looking at the pressures on my gauges on the high and low sides of the system.

So high pressure side would be the side after the condenser, and low pressure side before the compressor.

Reason I was expecting the front fan to come on when air conditioning is activated, is because good airflow is required for the condenser to operate efficiently and condense the hot high pressure gas from the compressor into a high pressure liquid.

When there is not sufficient air flow to allow efficient condensation from gas into a liquid, the pressures after the condenser will continually ramp up getting higher and higher until it switches off, blows a safety valve or something breaks usually.

This is what's happening on this vehicle, pressures keep ramping up, and fan is not cutting in.

I realise it's not on the vehicle triggered by a pressure switch, so I was expecting ecu to switch it via negative as soon as Aircon was switched on.

But as you have said and as I read it doesn't come on until 28-29 degrees it's why I've not witnessed it running automatically.

But I know that airflow is why the pressures are ramping up, because when I manually activated the front cooling fan the pressure on the high side dropped to what id consider normal.

So, I can only conclude, as the frontal fan is not designed to come on until 28-29 degrees, and obviously the pressures aren't supposed to keep ramping up and up either until something breaks.

That the problem must be with the viscous fan not generating enough airflow, certainly doesn't have the jet engine sound I've heard from other viscous fans and did seem quite slow in rotation.

yes, it seems that the viscous unit might not work well... try to stop it with a rolled newspaper when the engine is at working temp and if you can it means it doesnt lock... that viscous fan is able to ''suck'' realy hard through the radiators if it works well

Bit of a long shot but has the aircon been turned off in the ECU with a nanocom or something?

rigsby999 said:

Bit of a long shot but has the aircon been turned off in the ECU with a nanocom or something?

Click to expand...

Not that I can see, compressor is working.

I never realised that the fan only came on at around 28-29 degrees. So I was struggling to understand why it wasn't coming on and assumed it was faulty.

Because almost every other car I come across, the front mounted fan or a fan comes on either when air con is switched on... Or is activated by the increase in pressure from compressor starting up. That is pretty much the norm even on other cars I come across with a viscous fan.

However, I've since read online, and on here that it doesn't activate till 28-29 degrees, lol and as it never reached that outside i guess it shouldn't be coming on.

So only other conclusion I can come to is, that it only comes on as a supplement at a temperature of 28-29 degrees which I guess was the designers view is the temperature where the viscous will start to struggle and any other time they must of deemed the viscous fan to be sufficient.

So if this viscous fan is faulty, it would explain the lack of airflow leading to higher than normal pressures.

I don't want to leave it like that, as I was watching the pressures, normally in 25 degree heat id expect 10-15 bar as normal... 20 at a push on some vehicles... But this just kept going up and up... Went past 20, 25, 30, 35 bar... At which point I shut it off otherwise something was just going to go bang.

I know it's not an air con fault causing pressures to do that, because I jumpered the relay terminals manually switching the fan on, and pressures stabilised at 20 bar, still not great but at least it was stable.

So airflow is definitely the problem, I just assumed it was a fault with the fan wiring or something because it's not usually the norm for a front mounted fan to operate in a supplementary manner.

Guess next step is to get a replacement viscous on it, and see what happens. But a viscous will definitely pull more airflow than the front mounted fan so I would hope the pressures will be nearer the 10-15 bar figure.

I'm sure it's presently faulty, because I know working viscous fans roar like that reverse on a jet engine... This certainly wasn't even when hot, and it looked to be rotating quite slowly.

there might be two problems then:
1. non locking viscous fan(i told you how you can test it to make sure but as you describe it it's just freewheeling there
2. faulty pressure switch, cos L.R. designed it to stop the compressor above 32 Bar when rising but makes the compressor to start at 26 Bar when the pressure is decreasing so for LR is normal for the system to work continuosly if the pressure is let's say 30 Bar
(i'm not an aircon expert like you so i reluy only on the data delivered by the builder)

RAVE - AIR CONDITIONING - DESCRIPTION AND OPERATION 82-17 said:

Dual pressure switch
The dual pressure switch protects the refrigerant system from extremes of pressure. The normally closed switch is
installed in the top of the receiver drier. If minimum or maximum pressure limits are exceeded the switch contacts
open, causing the compressor clutch to be disengaged. The minimum pressure limit protects the compressor, by
preventing operation of the system unless there is a minimum refrigerant pressure (and thus refrigerant and
lubricating oil) in the system. The maximum pressure limit keeps the refrigerant system within a safe operating
pressure.

Dual pressure switch nominal operating pressures

Limit -----------Opening pressure, bar (lbf.in 2 )----Closing pressure, bar (lbf.in 2 )
Minimum = 2.0 (29.0), pressure decreasing - 2.3 (33.4), pressure increasing
Maximum = 32 (464), pressure increasing - 26 (377), pressure decreasing

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you've concentrated on that electric fan but it's purpose is only to help the airflow in the mentioned conditions...i can tell you that i went through a summer with it seized untill i realised that it must blow colder but the aircon didnt suffer any damage so i presume the dual pressure switch worked and protected the system when the pressure got above limit

sierrafery said:

there might be two problems then:
1. non locking viscous fan(i told you how you can test it to make sure but as you describe it it's just freewheeling there
2. faulty pressure switch, cos L.R. designed it to stop the compressor above 32 Bar when rising but makes the compressor to start at 26 Bar when the pressure is decreasing so for LR is normal for the system to work continuosly if the pressure is let's say 30 Bar
(i'm not an aircon expert like you so i reluy only on the data delivered by the builder)


you've concentrated on that electric fan but it's purpose is only to help the airflow in the mentioned conditions...i can tell you that i went through a summer with it seized untill i realised that it must blow colder but the aircon didnt suffer any damage so i presume the dual pressure switch worked and protected the system when the pressure got above limit

Click to expand...

Hi, thanks for the information, yep I know now the fan is only an assistance fan, I was only concentrating on it because the condenser has an airflow problem and most cars the fan comes on, but now know it doesn't on here as it is for assistance only. So problem would seem to be with viscous fan, I will test this next time and replace if necessary.

Didn't know the upper limit set on the pressure switch but would seem that is faulty also.

30 bar maybe the cut off limit, and 26 the cut in limit but those pressures aren't ideal for normal running. It strains the compressor reducing its lifespan, increases load on the engine and any weak points in pipes or condenser radiator or hoses and it can blow out. 30 bar is 435psi lol so any higher and something would definitely be exploding.

Just looked at price on those switches and they cost a fortune for some reason £70+