Air conditioning question for a 2005 BMW 325i

Last summer, my air conditioning was blowing hot air. I took it to the mechanic where they added refrigerant. It worked. Last week, it was blowing coolish warm air on the driver side and warm air on the passenger side. I took it to the same mechanic where they added refrigerant. Now, it blows very cold air on the driver’s side and cool air on the passenger’s side. I inquired about a leak, but they said that they didn’t see one, but I could take it back in a couple weeks where they could run a dye to determine whether there really is a leak. They also mentioned that I might need to bring it every year to have refrigerant added.

I read a few articles and have concerns that they would just add refrigerant, (especially a second time) without determining the root cause of the problem. I’m also wary that they would suggest bringing it back every year and at a cost of $110, especially when I read that an unrepaired leak could have an adverse impact on other related components. Prior to reading this I was thinking of adding coolant myself every year for closer to $35. I’m also wondering why the driver’s side is blowing colder air than the passenger’s side and whether there could be a larger issue than just a leak.

All feedback is greatly appreciated

You are correct the AC is a sealed system so there has to be a leak somewhere. Given the price to service a BMW air conditioning system I’d go the $35 refresh the refrigerant annually.


Now that it has been fully charged, they can’t add a dye unless they remove the refrigerant they just added. Your best bet might be to wait until next year and make sure that if you get a recharge, that they add the dye at that time.

Sometimes, if you don’t use your AC during the winter, the system will leak. If it is not done automatically, then be sure to turn on the AC in winter anytime you turn on the defrost. That will help the system keep in shape.

But your mechanic should do one very simple test and that is to test the schrader valves in the high and low side ports. This is where he hooks up his gauges when he checks the system pressure and/or add freon. Sometimes these begin to leak after they are disturbed when the gauges are hooked up. Its a simple fix as well.

The difference between the drivers side and passenger side cooling is a different issue altogether, probable due to a blend door mis-adjustment.

@keith you CAN add dye to a charged system

It gets sucked in through the low side when the AC is operation and the engine’s idling

Don’t need super fancy equipment

Done it hundreds of times

Dye can certainly be added to a fully charged system and so can refrigerant oil. Personally, my preference is the use of a sniffer to detect leaks.
I’m no BMW expert but the vent temperature difference is likely to be a door malfunction inside the dash.

Some things to keep in mind.
An auto A/C is not sealed like a home central unit. Some leakage can be expected even when new although the amount is so trivial as to be meaningless. Over time that leakage increases and a 9 year old car can be reasonably expected to become a problem.

Having it recharged every year is not the proper answer and some places have laws against recharging A/C units that have known leaks.

With refrigerant loss there is usually some refrigerant oil loss. Often what happens is the refrigerant is replaced but not the oil. Over time this can lead to compressor damage from oil starving.

I’m not a fan of stop leak products but seeing as how the leak on your car is apparently small you might consider adding a can of refrigerant which has oil and a stop leak additive in it. That could work well enough to stop or at least dramatically tame any leak.
The usual suspect with automotive A/C leaks is a compressor shaft seal and the service ports that are used to connect A/C gauges during charging may also leak; sometimes due to being disturbed by the gauge connection. Just some random info and hope it helps. :slight_smile:

I think the difference in vent temperatures is caused by a low refrigerant charge. It’s quite easy for a shop to add dye to a system and then have you return in a few days to inspect for leaks. However, generally the initial testing is done with a hand-held leak detector.

If it was fully charged last summer and needs to be recharged again the leak should be able to be found with a leak detector and/or dye if the mechanic is patient enough and checking properly.

Whatever they eventually find it’s going to cost a lot more than $110 to repair…

Wanted to thank everyone for their feedback, much appreciated

Fixing any problem will be expensive? Self fulfilling statement? It has leak! Therefore it is expensive? Bad pressure line? Evac, change hose, recharge. $400. Bad condenser? $900. Bad evap? $1100. Bad compressor? $1300. Darn, you are right. All expensive.

The air flow and mix fresh/recirc is controlled by motors that move flaps. These not working would cause temp changes.

Sounds the same as one of mine. Went through this cycle twice before getting it diag’d …in the WINTER
during the winter cold months, the little o-rings contract from the cold and freon leaks out. With a dye in place you might find NO leak during the warm summer months. But just wait till the cold months when you don’t use it. THEN they’ll find the very slight slow leak and replace a few dollar o-rings to fix that.