A/C Temp fluctuating

Hey I'm new to the whole Legacy scene and I was wondering if it is normal for the A/C to blow really cold and then just mildly cold?? Just the temp changes not the fan speed.

Thanks for any help in advance.

Notice a correlation between temp and engine load? Mine fluctuates based on engine load, which I assume is normal, tho it does it more any other car I've owned.

Mine has always sucked. I remember a thread with other people commenting that theirs was not that great as well.

 

Now if it's good sometimes and sometimes it is not that great it may just be a higher outside temp and humidity issue?

Happens to mine as well. Although I seem to notice it goes warmer for 30 seconds after a moderate acceleration but during it usually doesn't change...

Thanks for the response. But everything you all have said doesn't match what mine does. It's ice cold for 60 sec and then semi-cool for about 30 sec (seems longer because its 105 degrees outside). This happens no matter what the temp is outside, no matter if the car is sitting sit or I'm cruising down the freeway. By the response I'm getting, I'm guessing this is not normal. I think I'll have it checked out.

The AC system on these cars is really small, so it doesn't have much cooling capacity. With mine, the low AC refrigerant volume makes the system cycle on/off too much, even with the refrigerant amount set absolutely spot on. When it cycles off, there is no refrigerant flow, so the evaporator temp goes up, and vent temp goes up.

 

Best way I've found to get the AC to be consistently cold on hot days is to keep the engine speed low. 1500rpm seems to be the butter zone. Lower than that and the compressor can't move enough refrigerant. Higher than that, and it moves too much refrigerant, makes too much of a pressure drop across the oriface and makes the compressor cycle off. And at idle, switch the AC to recirculate.

Different car, but this happened in our Camry and it turned out to be a leak in the air conditioning system that was letting outside air into the tubes...water condensed, then froze, blocking the air from the compressor from reaching the cabin. It had similar symptoms- it would run briefly on startup for anywhere from a few to about 20 minutes, then would just start blowing warm air.

It has to do with how hvac works. It doesn't always compress the refrigerant. So once the refrigerant has given up all the endothermic energy the compressor kicks back on hence having cold air!

Tangent:

Anyone have any information on the diverter flap which controls feet to face. When I have it go to both it doesn't seem to stay closed all the way.

 

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The temperature variation is pretty normal as the a/c compressor clutch engages / disengages (aka cycles so the evaporator doesn't freeze up, keeps the correct thermal efficiency, etc etc.). Especially for the Legacy. Also when you get hard on the throttle many newer cars will disengage the compressor clutch to provide more power on acceleration and a slew of other reasons.

get used to it. It's normal.

Could be that you are bumping up against a low pressure cutout switch if you are low on refrig (if our cars have that option) but it is usually normal ops for the comp to cycle to some extent.

I came here to ask something similar... noticed it blows ice cold at times and luke warm at other times. I figured it was related to engine load but had not given it much more thought.

I came here to ask something similar... noticed it blows ice cold at times and luke warm at other times. I figured it was related to engine load but had not given it much more thought.

 

do some searching, tons of threads on this.

do some searching, tons of threads on this.

 

No need to, this thread already covered it.

No need to, this thread already covered it.

 

along with the other 500.

I just found this thread today, after I added a can of refrigerant yesterday and my AC stopped working.

 

Like others here, my AC blows anywhere from very cold to mildly cold, and I thought it was a leak. I put an AC gauge on it and it was at the top of the green zone, but I added a can of "ArcticFreeze Ultra Synthetic Refrigerant 134a+" - it is a 12oz blue can from WalMart - to try and top it off. It seemed a bit cooler immediately afterwards, but 4 hours later when I started the car the compressor just cycled on and off in 2 sec. intervals like it was unable to start. I attached the AC gauge and it was in the red, so using a small pick I released pressure from the low side until I was back at the top of the green. Now my AC works again, just as well as it did when I began. The lesson here? Get used to it, it's not broken.

 

One final question though, how precise does the AC volume/pressure need to be? Am I risking damage to my system now that I've changed it?

The AC system on these cars is really small, so it doesn't have much cooling capacity. With mine, the low AC refrigerant volume makes the system cycle on/off too much, even with the refrigerant amount set absolutely spot on. When it cycles off, there is no refrigerant flow, so the evaporator temp goes up, and vent temp goes up.

 

Best way I've found to get the AC to be consistently cold on hot days is to keep the engine speed low. 1500rpm seems to be the butter zone. Lower than that and the compressor can't move enough refrigerant. Higher than that, and it moves too much refrigerant, makes too much of a pressure drop across the oriface and makes the compressor cycle off. And at idle, switch the AC to recirculate.

 

This is far and away the most informed post I have seen someone write about the A/C system in these cars, which is unfortunately not saying much for this forum.

 

 

The problem that most people describe here is NOT normal operation. Everyone needs to stop saying "oh that's normal" every time the issue is brought up. The A/C compressor should not cycle off for long enough periods of time to net a 40°F variance in vent temperature when it's only 80°F outside.

 

You more or less brushed over the issue -- the low pressure switch is being triggered, which disengages the compressor. Whether or not this is correct, I don't know. My last car had a hidden diagnostic system that literally told you "I have turned off the compressor because:" followed with the many reasons that could happen (high pressure, low pressure, throttle >60%, rpm > 4750, rpm < 850, etc.) I have yet to find a similar diagnostic function for the LGT -- I certainly can't find it here, since every catastrophic problem with LGTs are "normal operation".

 

Short of tapping into all the available sensors around the A/C system and displaying a list of resistances, I'm a little lost on how to see what it's doing. I very recently picked up a VAG-COM cable, but I haven't paged through the list of data points I can log yet.. I'm pretty sure the ECU doesn't take inputs form the A/C system outside of "it's on".

 

From what I can tell, about a quarter of LGT drivers report consistent cold air from their vents, with the remainder experiencing this excessive cyling issue. Nearly every single case where the original owner of this car describes the issue contains the phrase "when the car was new, it never did this".

 

I have this suspicion that the capacity listings for the LGT A/C system are incorrect, so every a/c shop including the dealerships are putting in incorrect amounts. Similar things happen all the time (look up a serp belt for a non-S first gen mini cooper, for example). The reason I say this is because I have had almost the entire system replaced due to a collision and I saw no change in the problem, so it's a freon issue or an issue with a component near or behind the firewall.

 

Has anyone who is actually qualified to touch an A/C system looked into this issue in depth?

pretty sure the OP has a major leak and is low on r134. That's why the A/C is cycling on and off, because there is not enough refridgerant, and once it realized that, it shuts off.

 

60s on/30s off is a huge timeframe for a low pressure condition. Usually you see that in 2, 5, or 10 second intervals -- the compressor runs until low pressure is hit, then turns off for a minimum duration or until the pressure is above a certain threshold, whichever is longer. If it takes 30 seconds to get back up to that pressure, you'll drop below it again WAY faster than 60 seconds.

 

Granted, the majority of my experience has been on R-12 and early, pre-OBD2 134a systems.

I just found this thread today, after I added a can of refrigerant yesterday and my AC stopped working.

 

Like others here, my AC blows anywhere from very cold to mildly cold, and I thought it was a leak. I put an AC gauge on it and it was at the top of the green zone, but I added a can of "ArcticFreeze Ultra Synthetic Refrigerant 134a+" - it is a 12oz blue can from WalMart - to try and top it off. It seemed a bit cooler immediately afterwards, but 4 hours later when I started the car the compressor just cycled on and off in 2 sec. intervals like it was unable to start. I attached the AC gauge and it was in the red, so using a small pick I released pressure from the low side until I was back at the top of the green. Now my AC works again, just as well as it did when I began. The lesson here? Get used to it, it's not broken.

 

One final question though, how precise does the AC volume/pressure need to be? Am I risking damage to my system now that I've changed it?

 

Not sure on how exact it needs to be but I do know that you can't always just add refrigerant to the car as AC systems are very touchy and if it has too much pressure it will not work properly.