D4 A/C Compressor issue

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Originally Posted by scarry

Viscous fan may also have an electric overide,but i dont know how it operates,or what controls it.

At idle,to get the head pressure up to those sorts of pressures i would presume virtually no air would be going over the condenser.

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Viscous fan has electronic control managed by the ECU that allows it to go from slipping to 1:1 locked, using a rising voltage to increase the speed.

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Originally Posted by haydent

Here I was thinking it was a separate thermo fan turning on a minute or so after startup, but it must be the viscous ramping up.
I ran the test again (everything cold) and this time pressure didnt go so high, much more stable, will try again another day. Maybe this time due to ambient temp being a bit lower. Engine is TDV8

Attachment 182881

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Everything looks good now.. Happy days

You can see viscous control signal charted in last image, tests are done in carport at idle not moving. I will try again when warmer.

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Originally Posted by haydent

You can see viscous control signal charted in last image, tests are done in carport at idle not moving. I will try again when warmer.

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Seems the fan got up to over 5000RPM?

Maybe I am missing something,or reading the data incorrectly?

They do a self test occasionally on start as well,and will roar away,which is normal.

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Originally Posted by scarry

They do a self test occasionally on start as well,and will roar away,which is normal.

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Viscous fans all do that (electronic or thermostatic). When the fluid is cold, it's so thick the fan is effectively locked up. It takes 30 or so seconds for the fluid to warm to a point where there's the ability to control the fan. In my case it's usually backing out of the driveway and getting about 4 houses down the road before it starts to back off. If I hold it in 1st gear a bit longer it backs off quicker.

It's a good indicator of fan health also, because as they age and the fluid shears (or usually leaks) the severity of the startup roar decreases.

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Originally Posted by BradC

Viscous fans all do that (electronic or thermostatic). When the fluid is cold, it's so thick the fan is effectively locked up. It takes 30 or so seconds for the fluid to warm to a point where there's the ability to control the fan. In my case it's usually backing out of the driveway and getting about 4 houses down the road before it starts to back off. If I hold it in 1st gear a bit longer it backs off quicker.

It's a good indicator of fan health also, because as they age and the fluid shears (or usually leaks) the severity of the startup roar decreases.

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I have no roar anymore. Never. Not hot, not cold [emoji848]

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Originally Posted by DiscoJeffster

I have no roar anymore. Never. Not hot, not cold [emoji848]

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I'd be keeping a periodic eye on your temps, particularly on the hotter days. Unless they drop a seal, these things tend to "age gracefully", so you won't notice it's not doing the job until it no longer does the job. Unless the vehicle is under extreme duress, there is plenty of "spare capacity" to allow for wear and tear.

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Originally Posted by BradC

I'd be keeping a periodic eye on your temps, particularly on the hotter days. Unless they drop a seal, these things tend to "age gracefully", so you won't notice it's not doing the job until it no longer does the job. Unless the vehicle is under extreme duress, there is plenty of "spare capacity" to allow for wear and tear.

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I’ve suspected it for a while as the AC warms up when stationary in traffic and doesn’t come back until I’m moving. 13 years and 325k Km. Probably has seen better days

I’ll have to get the GAP out and take a look

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Originally Posted by BradC

Viscous fans all do that (electronic or thermostatic). When the fluid is cold, it's so thick the fan is effectively locked up. It takes 30 or so seconds for the fluid to warm to a point where there's the ability to control the fan. In my case it's usually backing out of the driveway and getting about 4 houses down the road before it starts to back off. If I hold it in 1st gear a bit longer it backs off quicker.

It's a good indicator of fan health also, because as they age and the fluid shears (or usually leaks) the severity of the startup roar decreases.

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I am sure ours didn’t do it every start,when cold,although that is from an aging memory.🤣🤣

A bit more info here on the viscous fan,and it’s operation,and what the ECU actually looks at to control it.

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