[Calvinf13]

Intermittent A/C blows heat. Not warm air like it's low on refrigerant. Then sometimes it will just start blowing cold. Any ideas? It's a 2010 328i.

[marvinstockman]

Low coolant.

[clegg]

You can buy a can of R134 with the gauge built in at any auto parts store. Add slowly and if the ac begins to cool, you in fact are low on refrigerant. If low on 134 though, you more than likely have a leak in the ac system.

[gbalthrop]

Originally Posted by Calvinf13

Intermittent A/C blows heat... Then sometimes it will just start blowing cold. Any ideas? It's a 2010 328i.

You have a "Mixed Air Flap" on Each Side: Driver & Passenger, which is controlled by the Thermostat on that side. Those two flaps direct air which has passed through the A/C Evaporator (Refrigeration) coil through the Heater core when it needs to be warmed to achieve T-Stat setting, OR NOT if FULL A/C is requested. The incoming air ALWAYS goes through the Evaporator/ Cooling coil, so if it is suddenly being heated when A/C (cooling) is requested, then the flap motor(s) or it/their control is/are "going Rogue" and NOT being properly controlled.

That can be confirmed using INPA which shows Flap Position of EACH of the EIGHT (8) Flap Motors. I'll attach two different INPA screens to next post, showing (1) "0%" Mixed Air Flap position on both sides when Full Cooling is requested, and (2) "80%" Mixed Air Flap position on both sides when T-Stats set to 24C and outside Temp is 3C (Heating mode). So NO air going through heater core on Full Cold, and 80% through heater core in stated heat mode.

You might try pressing "MAX" button in center of Left T-stat, and see if that prevents intermittent flap position change. Also check and see if air temperature is same from vents on BOTH sides.

Please let us know what you find,
George

[gbalthrop]

Per prior post, attached are the two INPA screens described above.

George