Warm air from one a/c center vent?

[andrewwynn]

Unless like in several cases where I've had low freon cause icing of the evaporator. Blocks the airflow. Turn off the AC and run vent a few minutes if the AC comes back on cold your evaporator was likely iced. The sensor in the airflow can't tell if the evaporator is iced so the compressor stays running.

If you find that your freon was a little low and topping it off stops the warm/cold/warm cycle of your AC you'll be happy I had the same problem first.

You can report back but you do not have to run recirc to get ac to run cold unless ambient temp is over 100f.

So: when wife's new to us e53 was first acquired the AC would blow very cold for ten minutes then with fan on high the speed of air would slow down and there would be air coming out that was a little colder than ambient. If I set the AC to vent for five minutes blowing outside air though the system the air world start to blow faster as the evaporator defrosted and when I turn the AC back on full blown icy cold AC.

When I hooked up the manifold sure though the low side was low but high enough to pass the low pressure test. Added a few oz of r134a and 40° air out the vents and the frozen evaporator issue went away.

The car has a sensor to stop evaporator from icing but I believe it's in the air stream which will be above freezing if the evaporator ices up.

I've had several cars where this happened and only happens on humid days and when freon was low but not terrible low.

[andrewwynn]

Originally Posted by BondoBen

And this would occur in one of the four vents? I've read where people have checked the Freon level but never understood how/why one of the four vents would be affected. I'll check that but in the mean time......how does it just affect the one vent with only one common evaporator? Thanks.

Yeah if evap freezes it'll affect all the vents but not exactly the same. Some vents are favored so when the flow is weak the weaker vents will get hit the worst.

I usually have my center vents slightly closed to force more air to the side vents by the window where the sun hits me.

You could have a vent flap problem but there's no internal left/right flap just the outside air and recirculating flaps but I haven't taken it apart on e53 there might be separate flaps for mix left/right.

[BondoBen]

Well......and I apologize for this.....I did recharge A/C 2 weeks ago. Had little in it. It's been without A/C for 4 years now. Finally got the aux fan to work which then allows A/C to work. All is well until yesterday when this warm cold started. There's dye n the system and I'm afraid it's the evaporator core. I changed the TXV and noticed a tiny bit of dye around the core's inlet and outlet. Was hoping it would become nothing. Will check pressure tonight. Thanks for the insights. I will follow up on Thursday.

[80stech]

If the compressor is stuck at full volume you can get evap freezing as well. Again, use recirc and see if that helps to give some direction.

[BondoBen]

So I checked the pressures with my gauges and sure enough......they read low. 6 and 60. So I'm thinking I must have a leak somewhere let's just add some Freon and see if I can find it. There's dye in the system so it should reveal itself......right. Can't find it. Prior to this I had taken all the hoses apart , replaced the o rings, replaced the TXV, and blew air through system to make sure there were no blockages. So there is some residual dye showing around these parts. But nothing that would seem like a leaking component. I've now washed/scrubbed the engine bay and around the TXV. Everything I replaced has been cleaned with almost no signs of dye. One would have to look very very close to see anything. Trying to recharge the system didn't seem correct. Could only install 150g of Freon and the pressures were 22 and 166. Blew cold......but then again that middle left vent went to warm and then cold and warm again. Previously the pressures were 45 and 255 after a vacuum that held for 4 hours. No matter what I do.....that's it. That's all I could get out of the system. I got frustrated and shut the car off and started something else. An hour later the gauges were reading 75-80 on the low side and 45 on the high. As time passed on the high side went down to 1.7 while the low side held. Cannot see any signs of dye anywhere. Only places I cannot see is inside the evaporator housing past the TVX, the internal compressor, and the underside of the condenser. Any thoughts/ideas I would appreciate. I thought finding this leak using dye would be easier I guess. And thanks again for the help.

[80stech]

You probably have more than one problem at this point. Even the tiniest drop of moisture will cause the expansion valve to freeze and cycle. It could be that the desiccant is saturated and maybe even the bag has broken, if you looked carefully you might have seen some desiccant at the TXV when you replaced it if that is one of the problems. You know you need a UV light to see the dye right ?

[X5chemist]

Did you change the valve cores? I find that mysterious leaks are mostly likely bad cores. Cores are the weakest points on an A/C system.

[BondoBen]

Yes.......had changed cores when I had system apart for new O rings. Removed condenser cause now auxiliary fan quit. Tested fan every which way I can and nothing. So while I had front end apart......let's just take a peek at the sock. Totally saturated with oil. Like a sponge just dripping oil. Not being knowledgeable regarding refrigeration I'm just guessing here but that doesn't sound right. Ordered new sock (dryer) and flushed condenser out. Awaiting arrival of both parts. Now I'm thinking about how that sock should have looked. If there's oil in the system........how much should that sock contain? Again.......what would it look/feel like? Also this system has a separate left/right temperature adjustment. I just didn't understand the left center and far left vent blowing drastically different temps. Thanks for the input/advice.

[X5chemist]

Refrigerant oil capacity is 3.72 fluid ounces. Each major part will have a portion of it. Some will flow through the entire system. Rub oil on o rings before installation. A good size portion of oil will be at the compressor. It's the lowest point.

[80stech]

Yeah, the desiccant bag should not have been soaked with oil. Checking and/or getting the oil level right is not straight forward. Maybe time to take it to a A/C shop ??