Weird AC Issue

[Fifty150hs]

Hi Guys. 2006 3.0 with an odd problem, a couple actually.

1. Every so often when I start the X with the AC on it makes a loud "whoooot" sound behind the dash. Only happens once and the AC works fine after that.

2. It has been super hot here (for the SF Bay Area) and in the high 90's, low 100's. When I fire it up after it has been sitting and the inside is an oven I put it on MAX and it will start to blow cold and then it doesn't, until I start driving. It then starts to cool down, until I have to stop at a light, it then starts not cooling well until I move again. The electric fan is working, in fact it is howling it is running so fast. I put a gauge and refill can on it (I don't have AC equipment) and it shows good pressure on the low side. The manual says it shouldn't be above 35 psi ever. It's at 35. Any ideas? Would a failed fan clutch cause this?

[X5chemist]

The blower motor bearings are starting to fail. Mine whines at start up now and then. If you have a mechanical clutch, replace it if it's old. It will help with A/C cooling. Low pressure can be good, however high pressure is important too. At 100F, low pressure should be higher. It should be in the (45 is acceptable) 50-55 PSI range. 275-315 PSI on high side. My 3.0 has a brushless auxiliary and mechanical fan. Once the engine is to temp, it can maintain 42F in dead slow traffic and stop signs.

[Fifty150hs]

Originally Posted by X5chemist

The blower motor bearings are starting to fail. Mine whines at start up now and then. If you have a mechanical clutch, replace it if it's old. It will help with A/C cooling. Low pressure can be good, however high pressure is important too. At 100F, low pressure should be higher. It should be in the (45 is acceptable) 50-55 PSI range. 275-315 PSI on high side. My 3.0 has a brushless auxiliary and mechanical fan. Once the engine is to temp, it can maintain 42F in dead slow traffic and stop signs.

Newtis says the low side should never be reading higher than 35 psi. I've put more in before and it causes the auxiliary fan to really run fast. When it's not crazy hot like it has been here the AC works fine.

[X5chemist]

35 PSI for 100 degree weather? I go by R134 chemical properties. Google R134 pressure charts. I'm sure mine is in the 40's. If the fan is blasting at full speed, pressure is building up in the A/C system. Or the engine needs extra cooling. My X5 had an A/C system replacement done before I bought it. I have no idea how much was replaced. It was winter time. I know the auxiliary fan was not working when temps started to rise in the spring. I replaced it but I was not satisfied with the running temp. I did a complete vacuum and recharge on it. It's been running ice cold ever since. A reading on the high side would be helpful. Both readings tell if the complete system is working properly.
Here is a list of how both pressures can be interpreted: https://rechargeac.com/how-to/ac-system-pressure-chart/

[Fifty150hs]

Originally Posted by X5chemist

35 PSI for 100 degree weather? I go by R134 chemical properties. Google R134 pressure charts. I'm sure mine is in the 40's. If the fan is blasting at full speed, pressure is building up in the A/C system. Or the engine needs extra cooling. My X5 had an A/C system replacement done before I bought it. I have no idea how much was replaced. It was winter time. I know the auxiliary fan was not working when temps started to rise in the spring. I replaced it but I was not satisfied with the running temp. I did a complete vacuum and recharge on it. It's been running ice cold ever since. A reading on the high side would be helpful. Both readings tell if the complete system is working properly.
Here is a list of how both pressures can be interpreted: https://rechargeac.com/how-to/ac-system-pressure-chart/

I'm going to rent or buy a gauge set and check the high side. Something is definitely off. My need to be drained, and refilled.

[Fifty150hs]

This is what it says in Newtis for normal pressures:

Connect service station to car and open both valves on the charging hoses. Adjust A/C system at control panel as described for A/C efficiency measurement.
Note:
The following values apply as normal pressure ranges for ambient temperatures between + 20°C and + 40°C:
Inlet pressure: 1.0 - 2.2 bar
Outlet pressure: 12 - 22 bar

2.2 bar is just under 32 psi. 40C is 104F.

I don't understand why that differs so widely from system pressure chart.

[andrewwynn]

When hot ambient my low side was over 35. Let me look for pic.



45/245. It was quite hot that day. I recommend getting an AC manifold so you can see high and low at the same time.

The only way to get the correct charge precisely is to evacuate and weigh how much is put in.

When I did the car in the photo I just had a thermometer in the vent got the vent temp to 39f (90 outside).

It's guesswork without knowing the high side but with just low side you can measure pressure with the car not running you'll get a relative freon quantity but you'd have to get the same reading from a working car's baseline.

Some cars you can find a chart in their repair manual for the equalized pressure at different ambient temps.

[Fifty150hs]

Originally Posted by andrewwynn

When hot ambient my low side was over 35. Let me look for pic.



45/245. It was quite hot that day. I recommend getting an AC manifold so you can see high and low at the same time.

The only way to get the correct charge precisely is to evacuate and weigh how much is put in.

When I did the car in the photo I just had a thermometer in the vent got the vent temp to 39f (90 outside).

It's guesswork without knowing the high side but with just low side you can measure pressure with the car not running you'll get a relative freon quantity but you'd have to get the same reading from a working car's baseline.

Thanks Andrew. Clearly there is something amiss with BMW's numbers. I will be getting a manifold so I can check both sides.

[Fifty150hs]

Did the newspaper test on the fan to test the viscous clutch. Its shot. Completely shot. I'm surprised its spinning at all it is so easy to stop. Ordering new clutch. Will update after its in.

[Fifty150hs]

I had to wait to order the clutch. Won't have it until friday, but we're getting more real hot weather. So, I pulled the fan, drilled a hole and ran a screw into the clutch. Fan clutch is now locked up so the fan is spinning at full speed. Seems to have fixed the problem. Sounds like a truck from the loud noise from the fan, but its only for a little while. At least the AC works better.