[MrMCar]

Let's look at how many have issues with properly bleeding the cooling system, quite a few....
Now if the above is done properly and quickly, no cooling system bleeding becomes necessary.

However if everyone performed a system bleeding, I'd bet that 50% of the folks would create an issue that did NOT previously exist. This is an unwanted outcome.

 

[Dannyb80]

Let's look at how many have issues with properly bleeding the cooling system, quite a few....
Now if the above is done properly and quickly, no cooling system bleeding becomes necessary.

However if everyone performed a system bleeding, I'd bet that 50% of the folks would create an issue that did NOT previously exist. This is an unwanted outcome.

Yeah I get that it took me no longer than 20 seconds to pop it out and back in. I'd rather do it this way if I ever had to do it again even of for some reason it had to be bled after as bleeding it only takes 5 minutes, rather than draining the whole system. I inspected my old temp sensor and the wires wasn't connected must of been knocked at some point, new sensor has solved my problem.

 

[Sapote]

My question is the reason it's turning back off with the AC on because it's not cold enough hence not needing to stay on? I have my m.o.t on Friday so I am going to ask the

If refrigerant is low then pressure sensor tells the DME to turn off the fan as it’s not needed

 

[Dannyb80]

If refrigerant is low then pressure sensor tells the DME to turn off the fan as it’s not needed

Brilliant think I'm good to go fan is working again and it only cost £9 for the sensor. Thanks to everyone for all the advice and help 👍

 

[Effduration]

likely issues:

aux fan is not working
mechanical fan clutch has failed - do the newspaper test

we recently had a thermostat fail with symptoms like the ones you describe

fan issues are more common.

 

[Bali]

I have drove my car for 3 hours this morning normal and traffic driving no overheating and gauge perfect at 12 o'clock. My A/C is empty but when I press the AC button the electric fan now spins for around 30 seconds then goes off, before I changed the temp switch it didn't run at all even with the AC on. My question is the reason it's turning back off with the AC on because it's not cold enough hence not needing to stay on? I have my m.o.t on Friday so I am going to ask the garage to re gas my ac and see if it stays on.

What do the Engine and Climate Control fault codes show you?

 

[Dannyb80]

What do the Engine and Climate Control fault codes show you?

I think I'm all sorted now since changing the temp sensor, I inspected my old one and it must of got knocked as the top come off it so the wires wasn't connected. My aux fan now comes on which it wasn't doing before I changed the sensor. Also no faults codes checked before

 

[LeverThis]

I've NEVER had air in the above method. In fact you can see the liquid right there in the cavity.

If it did suck in enough air to warrant a re bleed, there would be coolant on the ground. After it chugged out, tantamount to an upside down gas can

I've done this method even without compressing the upper hose, and never had to re-bleed.

 

[LeverThis]

Also no faults codes checked before

The A/C may need a simple recharge or it could be more complicated.

There might be no generic engine fault codes (Pxxxx) which is what most scanners look at, but a scan of the IHKA module (climate control computer) might reveal codes relating to the non-functional A/C.

 

[Sapote]

I've NEVER had air in the above method.

Interesting, as the law of Physics says air must be suck in; if not then the upper hose should not be able to return to its former round shape. What had filled in the extra volume in the system when the upper hose returned to its round shape as soon as the temp sensor was removed -- ether, coolant or air?

 

[LL i am]

Open up the radiator (expansion tank) cap half way. Squeeze the upper hose with all you've got. At the same time tighten the cap. Now your cooling system is under slight vacuum. air was expelled at this time
Have everything at the READY.

Pop the sensor out and have the new one slightly lubed. Make sure the old O Ring comes out, have a pick ready if not. Pop the new sensor in and make sure it clicks. Give it a tug to be sure it's ALL the way in. Reconnect the electrical connector.
Open up the cap and top off. same air returned to the ET, of course without spelling it out, you would close back the cap

Loss should be minimal.

Interesting, as the law of Physics says air must be suck in; if not then the upper hose should not be able to return to its former round shape. cap was opened again, hose returned to former round shape pleasing to our eyes What had filled in the extra volume in the system when the upper hose returned to its round shape as soon as the temp sensor was removed -- ether, coolant or air? both, thru the open ET, should be minimal.

 

[Sapote]

"cap was opened again, hose returned to former round shape pleasing to our eyes What had filled in the extra volume in the system when the upper hose returned to its round shape as soon as the temp sensor was removed -- ether, coolant or air? both, thru the open ET, should be minimal. "

No, as soon as the lower hose sensor was removed, the upper hose will return to its former glory round shape in less than a second, unless people be able to swap out the sensors in less than a second.

 

[LL i am]

No, as soon as the lower hose sensor was removed, the upper hose will return to its former glory round shape in less than a second,

there would still be coolant immediately occupying the area preventing air to come in, unless ambient air pressure is enough to overcome.

 

[MrMCar]

I'm not talking physics here. I'm sharing what has worked for me for over decades.
If you're uncomfortable with it, don't do it. Simple.

 

[LeverThis]

there would still be coolant immediately occupying the area preventing air to come in, unless ambient air pressure is enough to overcome.

Right. And assuming the rest of the cooling system is sealed such that no air can enter elsewhere.

When I did this almost no coolant came out, though I did the swap very quickly.

It's like a drinking straw with one finger covering the top opening. The liquid in the straw is held in place without air passing through the liquid.

 

[Sapote]

there would still be coolant immediately occupying the area preventing air to come in, unless ambient air pressure is enough to overcome.

Right. And assuming the rest of the cooling system is sealed such that no air can enter elsewhere.

Guys, if the upper hose had sprung back to its full round shape, then the system must have sucked something in when the sensor was removed. Let's discuss about this:
1. When the sensor was removed, do you believe that the system is no longer under vacuum pressure with an open hole where the sensor was used to be? In fact the new pressure in the system with the sensor removed is exactly the same as the ambient pressure. Do you agree?
2. If we agree that the system pressure is the same as ambience, then air must have been sucked in to change the pressure from below ambience to ambience. This air mass has 2 paths to go:
a) via the lower hose to the Tstat but since the Tstat is closed so this is a harder path.
b) via the radiator, and they eventually get to the upper hose under the bleeder, to be bled out.

 

[LL i am]

then the system must have sucked something in when the sensor was removed.

coolant

n fact the new pressure in the system with the sensor removed is exactly the same as the ambient pressure. Do you agree?

I don't agree. there is an upward...to the hole coolant pressure trying to escape.

If we agree that the system pressure is the same as ambience,

N/A

This air mass has 2 paths to go:
a) via the lower hose to the Tstat but since the Tstat is closed so this is a harder path.

the coolant can rush out to the hole from that area, but since u said tstat is shut...

via the radiator, and they eventually get to the upper hose under the bleeder, to be bled out.

coolant would rush in from via radiator. air can be on top of ET if they insist. no prob.

 

[Sapote]

Sapote said:
then the system must have sucked something in when the sensor was removed.

coolant

Wait a micro-second, there is no coolant floating in the air for it to suck in through the sensor hole. You're driving me crazy here. Where was the coolant that being sucked in via the sensor hole?

 

[LL i am]

not sucking in
trying to flow out

 

[Sapote]

If coolant trying to flow out, then what filled in when the upper hose returned to round shape?