[lowrydr310]

I searched and searched and saw many people commenting with the same problem, but no solutions.

When I first start my car there's warm air blowing out of the vents for several minutes, and then it starts blowing cold. Occasionally while stopped and idling, it's almost as if the AC shuts off and warm air blows again. NOT good when the defroster is on, because as soon as this happens the windshield fogs up with the moist air from the evaporator box.

I used INPA to check the mixer flaps, temperature sensors, temperature settings, and the pressure reading. All work perfectly fine, even the stratification mixer. My radiator fan also works fine; I used INPA to command it to run and it turns on without any issue.

With a cold engine not running, INPA is reporting 5 bar pressure, which is plenty for the compressor to work. After starting it jumps to 5.5 immediately and then while idling or even driving, it slowly starts increasing. I never saw it go over 9 bar, but even then it just briefly spiked there, normally settling around 7 bar.

Sounds like it could be a low refrigerant charge, however I just paid an alleged reputable independent BMW shop to recharge the system. Later when the behavior didn't change, I asked if they did a proper evac and refill based on refrigerant weight and they told me NO they didn't do that, so that's still a possibility.

Could this be a faulty expansion valve? Sticking closed so there isn't enough refrigerant on the low side for the compressor to compress?

I know a bad pressure sensor can cause issues, but I'm getting valid readings that I confirmed with a set of manifold gauges.

Then there's the other option of replacing the compressor itself. I'd hate to waste my time and the cost of refrigerant to replace an expansion valve only to find out I have to replace the compressor and charge the system again. Is there any way to test the expansion valve function and confirm that it's faulty?

[ptpending]

all petrol e9x may have issue with freon pipe on right carrier bar under hood
it is corrode due collecting dust from wheel arch behind heat shield
so the good idea is to replace this whole pipe or weld the new part in it
until this will done all recharges will be temporary
if this issue will not be remediated, the compressor will run on low oil and will die

[lowrydr310]

Originally Posted by ptpending

all petrol e9x may have issue with freon pipe on right carrier bar under hood
it is corrode due collecting dust from wheel arch behind heat shield
so the good idea is to replace this whole pipe or weld the new part in it
until this will done all recharges will be temporary
if this issue will not be remediated, the compressor will run on low oil and will die

But I have no leaks in my system. I inspected all the lines and they're fine, no corrosion.

[ptpending]

you have to remove pipe to inspect this particular part

[lowrydr310]

Originally Posted by ptpending

you have to remove pipe to inspect this particular part

But my system isn't leaking any refrigerant.

[ptpending]

why then you recharged your system ?
if it isn't leaking than your car could have factory refrigerant

[gbalthrop]

Originally Posted by lowrydr310

When I first start my car there's warm air blowing out of the vents for several minutes, and then it starts blowing cold. Occasionally while stopped and idling, it's almost as if the AC shuts off and warm air blows again...
I used INPA to check the mixer flaps, temperature sensors, temperature settings, and the pressure reading...
With a cold engine not running, INPA is reporting 5 bar pressure, which is plenty for the compressor to work. After starting it jumps to 5.5 immediately and then while idling or even driving, it slowly starts increasing. I never saw it go over 9 bar, but even then it just briefly spiked there, normally settling around 7 bar...
I'm getting valid readings that I confirmed with a set of manifold gauges...

If you connect manifold gauges, engine OFF for one hour or more:
1) What are the readings, High Side & Low Side? They SHOULD be same with system at "Equilibrium". INPA "Refrigerant Pressure" per high side Pressure Sensor should be SAME, except there may be ONE atmosphere difference between "Gauge" pressure & Absolute Pressure (INPA).

2) If you then Start engine with A/C Control Panel MAX button pressed, what are Low Side & High Side Pressures per Gauges, & what is Ambient Temp?

3) If High Side Pressure is NOT > 150 PSIG, within first minute of Engine/Compressor Operation, monitor for ~ 5 minutes & record approximate values/ fluctuations of High Side Pressure. Also use INPA to monitor Evaporator Temp, which SHOULD be < 10C when cooling & preferably < 5C.

With both Manifold Gauges & INPA, you SHOULD be able to diagnose the issue. It may be something as simple as LOW Refrigerant Charge. 5 bar Pressure at Equilibrium is LOW, particularly if ambient Temp is > 70F.

IF you add refrigerant SLOWLY & monitor gauges carefully, it is safe to Charge System by Manifold Gauge Readings & a Temp/Pressure chart such as:
https://rechargeac.com/how-to/ac-system-pressure-chart/

Please let us know what you find,
George

[lowrydr310]

Originally Posted by ptpending

why then you recharged your system ?
if it isn't leaking than your car could have factory refrigerant

My first step was thinking I'd just pay a shop for convenience and let them deal with it, thinking they knew what they were doing and would determine if it was a low charge, then evacuating and recharging refrigerant based on weight. It was only after I learned they didn't do any of that. The refrigerant charge wasn't/isn't the issue as I was never too low to cause the symptoms I'm experiencing.

I have manifold gauges and a vacuum pump now, and just replaced an expansion valve on another car (non-BMW) that I own, properly recharging that car and the AC works perfectly.

[lowrydr310]

Originally Posted by gbalthrop

If you connect manifold gauges, engine OFF for one hour or more:
1) What are the readings, High Side & Low Side? They SHOULD be same with system at "Equilibrium". INPA "Refrigerant Pressure" per high side Pressure Sensor should be SAME, except there may be ONE atmosphere difference between "Gauge" pressure & Absolute Pressure (INPA).

2) If you then Start engine with A/C Control Panel MAX button pressed, what are Low Side & High Side Pressures per Gauges, & what is Ambient Temp?

3) If High Side Pressure is NOT > 150 PSIG, within first minute of Engine/Compressor Operation, monitor for ~ 5 minutes & record approximate values/ fluctuations of High Side Pressure. Also use INPA to monitor Evaporator Temp, which SHOULD be < 10C when cooling & preferably < 5C.

With both Manifold Gauges & INPA, you SHOULD be able to diagnose the issue. It may be something as simple as LOW Refrigerant Charge. 5 bar Pressure at Equilibrium is LOW, particularly if ambient Temp is > 70F.

IF you add refrigerant SLOWLY & monitor gauges carefully, it is safe to Charge System by Manifold Gauge Readings & a Temp/Pressure chart such as:
https://rechargeac.com/how-to/ac-system-pressure-chart/

Please let us know what you find,
George

Thanks!

72 psi on the low side gauge at equilibrium, engine off, 24°C ambient temperature, matching the high pressure sensor value from INPA. My manifold gauge high pressure connector is broken (missing 4 of the locking balls, I'm not taking that risk) and I just got the replacement last night.

Evaporator temp started at 28°C with the car off (higher than ambient, car parked in the sun) then slowly creeps down after starting the car but never drops below 13C.

Pressure sensor never showed higher than 9 bar via INPA.

I got the new connector for my manifold gauges and will do more diagnostics this evening. I mostly do all my own repairs and major service, having done full rebuilds on several engines over the years, but figured I'd go for convenience on this AC issue on my 335 and pay someone $80 to check and recharge if needed. Issue was not fixed so I'm doing it myself, further reinforcing my belief that no shop is trustworthy.