A few weeks ago, the A/c stopped blowing cold air. I took the car to a tech shop and he said Schroeder (is that spelled right) valves needed replacing and the Freon was leaking from there. After replacing the valves and vacuuming the system and filling with freon, the a/c was blowing cold air. Twice, now, the system blew warm air and after awhile began blowing cold air then warm air again. Is there another leak somewhere. The compressor kicks in. The expansion valve has been replaced some years ago, so maybe the evaporator coil is bad. The next step is to take the car back to the tech shop and have it checked out. Any suggestions/ideas why the a/c system is doing this??
Last edited by MORRIE; 06-01-2019 at 03:52 PM.
Hey Morrie, speaking as a career refrigeration specialist and not car person even tho I am trying to work on that...I’d say if you had a leak you would NOT go from cold air to hot back to cold. If it was leaking “usually it just be a steady decline in the warm direction”. Cold than warm than cold to me sounds more like your compressor is turning off and on before the temp is satisfied. My vibe is more electronics vs mechanical. If your evap was bad it too would just be more of a straight to warm not a seesaw effect. Once again I responded with refrigeration tech info NOT car mech info.
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Curious too, when you say cold than warm than cold. What’s the time frame on this swing. A day or two or at a traffic light? City traffic or highway? Did you all know doing 70mph with the AC ON at that speed your car would cool your house. In traffic it barely cool a hampster cage.
The valves you speak of should have caps. So even if they were bad they shouldn’t have caused your leak. The valves you speak of are the same as your tire valves. Schrader valves.
can you check the pressures with the gauge? May be the evaporator is freezing up and it is sensing it and turning off compressor (or with low pressure sensor).
Are you aware that if you are accelerating briskly that the AC compressor shuts off? It will blow warmish air until you reach a cruising speed, then the compressor will engage again and cool air ensues. Effectively the car saves all of the horsepower for driving the wheels when needed. It's hard-coded in the electronics somewhere.
Marty
This is about the 3rd time this has happened this week. I drive about 15-20 minutes from my house to the gym in light traffic not over 55 mph in light traffic stopping for few traffic lights. It happened going to the gym and about 2 hours later when I left the gym. I checked to see that the compressor was turning over when I got home. It was but no cold air. BTW the tech said the rubber O-rings in the schrader valves tend to collapse over time. I just replaced the valves. I was told that I had a leak around The valves years ago so they were replaced. This is the 2nd compressor on the car. I hope it's not the evaporator coil. That involves removing the dash....been there done that. Thanks guys for your input. I'll take the car for a spin on the interstate Sunday and see what happens. I'll leave a response on this thread.
Last edited by MORRIE; 06-01-2019 at 09:04 PM.
You need to find a good AC tech.
Oh, and to remove the evap does not require the dash to come apart, just the glove box needs removing.
The easiest evap swap I have ever done is on a Z3.
Without a set of LP and HP pressures. This is all just guesswork.
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Last edited by magnetchief; 06-01-2019 at 09:30 PM.
Thanks Chief for the information about the evaporator coil. Yes I will.take my car to another tech.
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Evaporator, Yes.. I think only Z have it at a location which does not need the dash to come out.
I had to replace everything except the lines. If compressor is on, then there is sufficient refrigerant in it. You really need the gauges to fix this.
For me, the evaporator, condensor both were leaking. Easy to find with the dye and yellow glasses with that light
I agree. Some pressures would be the be best to tell everyone what’s going on.
Thanks man....appreciate your input.
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Today I was prepared to take my car to the tech. When I started the engine and I pressed the a/c button I could hear the compressor turn on. to my surprise Cold air began flowing from the vents. I drove about 5 miles to the grocery store, parked the car, did some shopping and then drove home. The A/c never stopped blowing cold air. I have no idea what happened but I am thankful for this unexplained happening. I will hold my breath when I start the engine tomorrow.
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How high was the temperature and humidity?
Any loose connection on the high low sensors caused this?
Do you have DIS? Can you scan and see any stored error codes...Not sure if it will record anything for this
No clue what caused it. Humidity was normal no sensor malfunction and no codes came up.
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It could be a restricted expansion valve. I believe it’s recommended you change the valve and the drier when doing an AC refresh. Could it be possible that the valve is sometimes restricted and sometimes not causing fluctuations in refrigerator to the evaporator therefore resulting in sometimes hot and sometimes cold air. A set of manifold gages and pressure readings will help diagnose.
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Thanks for all comments/suggestions. However the a/c system has resolved itself. It is working again.
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As Mr Bingley deduced in your other switch thread, alternating cold and hot could be from the evaporator icing up and then defrosting, due to the blower not working on 1-2-3 because of the resistor. Until a new resistor comes, see if running the AC on 4 keeps it working.
BMW MOA 696, BMW CCA 1405
Just make sure your cooling fans are working typically. If your electric fan is shot, then at stop lights and low speeds and certainly during start-up, you will get ambient air out of the vents. As long as you are driving, your AC will feel normal. I was experiencing these symptoms on my 328Ci, and eventually tackled it to the failed electric cooling fan. Once replaced, all was normal.
No it doesn't but was worth a try.
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The problem is back....cold air then warm air. The expansion valve needs replacing. Of course a new drier since the lines will be opened. I wonder should I replace evaporator coil while I have access to that as well.
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Hell I would.
It’s a known issue.
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Don't need to replace the evaporator coil unless it is leaking. Expansion valve and its HNBR O-Rings. Get a packet of those O-Rings from Autozone. Do a thorough check for leaks with the yellow glass and light and replace as needed. Also make sure the drain in the evaporator drain is clean and it is draining water.
Within 3 years, it is blocked again? Any residue in the lines?
I know you got lucky and yours started working, but both of my cars, the M5 and the M Coupe will exhibit this problem when it's VERY hot outside.
The AC will work if you are driving on the highway and there is constant load on the system. If you are in stop and go traffic in the city, it'll get warm when idling or stopped at lights.
Very annoying. Would like to know what the fix is. One of the only areas of cars I'm not familiar with.
Thanks!
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