Cold air when driving, hot air when idle

Tiny
TONY02
  • MEMBER
  • 2011 TOYOTA COROLLA
  • 150,000 MILES
The A/C blows cold air when driving but when I come to a stop and just idle it starts to blow hot air. I thought maybe it would be low on refrigerant. I evacuated the system and recharged it but still the same thing. I’m thinking it can maybe be the compressor because I noticed it stays engaged at all time, but I’m not sure if that’s normal for my type of car.
Saturday, August 8th, 2020 AT 12:12 PM

10 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
This could be a compressor but it could also be air flow over the condenser that is not cooling the Freon enough during idling. The only difference between you moving and not moving is the amount of air going over the condenser. So we need to start with two things. First, turn the engine on and A/C on and make sure the fans are both on. If not, let me know.

If they are, then we need to check the pressures of the system to try and tell what the issue is. Depending on what the pressure is will give us an idea as to what the issue is.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Let us know what you find with this and we can go from there.
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Saturday, August 8th, 2020 AT 12:25 PM
Tiny
TONY02
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Yes it’s only one fan and it is working and as far as the pressures go for the low side it is around 92 and high pressure is around 98 and the outside temperature at the time was around 89-90° F.
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Sunday, August 9th, 2020 AT 6:26 AM
Tiny
TONY02
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I was also thinking maybe a clogged expansion valve, but then again I want to be sure and eliminate all the possible causes to make sure.
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Sunday, August 9th, 2020 AT 6:32 AM
Tiny
KASEKENNY
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That is great info. Your pressures are pretty much equalized which is normally indicating that the compressor is not operating properly. The fact that you noticed it is staying engaged is another sign, as you noted. That is staying that way because the PCM is not seeing the pressure change so it is keeping the compressor engaged to try and achieve that. So if those pressures where with the compressor running then it is not building pressure.

Take a look at the attachment. If you had a clogged expansion valve you would have pressures like 200/70 because even though there is a restriction, your compressor would still create a pressure difference. This indicates the compressor is not building pressure. If it is coming on and engaging then the compressor is faulty.
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Sunday, August 9th, 2020 AT 10:18 AM
Tiny
TONY02
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Okay, so then it’s safe to say that the compressor is bad and I should replace it? And this wouldn’t have nothing to do with the AC low/ high pressure switches right?
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Sunday, August 9th, 2020 AT 10:32 AM
Tiny
TONY02
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But by the way I took those readings with the car off and has been sitting for a while, I didn’t take the readings with the car running.
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Sunday, August 9th, 2020 AT 10:53 AM
Tiny
KASEKENNY
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Correct. Based on this info it appears the compressor is not actually building any pressure. If the pressure switches were the issue then the pressure may be the same as this but the compressor would not be engaging. The pressure switches will prevent the compressor from engaging so the key to this is the compressor is engaging and the pressures are equalized. That points to the compressor not operating properly.
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Sunday, August 9th, 2020 AT 10:56 AM
Tiny
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Oh. I just saw that update. If those were with the car off then that is not the compressor. It could still be a compressor but we need to take those same readings with the engine on and A/C set to MAX cold.

Let me know what the pressures are with it on and we can go from there. Thanks
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Sunday, August 9th, 2020 AT 10:58 AM
Tiny
TONY02
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Okay, so I did it again with the A/C on set to max cold and for the low pressure side I got around 60 and for the high pressure side I got around 150 and the outside temperature was 90 F.
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Sunday, August 9th, 2020 AT 3:13 PM
Tiny
KASEKENNY
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Okay. That helps but doesn't change the outcome much. Take a look at the bottom section of this attachment and you will see that your low side is slightly high and the high side is clearly low. This indicates that you need to service the system. This means evacuate the system and pull it down into a vacuum and make sure it holds for about an hour. Then recharge the system properly and retest the pressures. If you get the same results, you need a compressor.

So it looks like you need a compressor. It may be worth trying again if you are not positive the system held a vacuum for an hour. Let me know if you have questions. Thanks
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Monday, August 10th, 2020 AT 6:49 PM

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