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Normal AC operation

Grinder67

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I’m bought my 17 back in November so no AC usage. With all the talk of evap core problems, I started trying mine to see if it works properly. Holding my hand in front of one of the vents (base GT) it blows cold for about 15 sec and then really cold for about the same. It seems to cycle like this as long as it’s on. Is this normal or is something up?
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seth21w

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I’m bought my 17 back in November so no AC usage. With all the talk of evap core problems, I started trying mine to see if it works properly. Holding my hand in front of one of the vents (base GT) it blows cold for about 15 sec and then really cold for about the same. It seems to cycle like this as long as it’s on. Is this normal or is something up?
Normal you will know if your evap goes if you put on defrost and get oily residue and a smell.
 

ahl395

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Most likely the compressor cycling on/off. Did you try this when idling, driving, or both? Premium or base?
 
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Grinder67

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Most likely the compressor cycling on/off. Did you try this when idling, driving, or both? Premium or base?
It is the compressor cycling on/off at the same intervals as the cold/colder temps. Seems to be the same idling or at speed. Base GT

I did stick a digital thermometer in the air vent and it shows about 39 on the colder side and 42 on the high side. (55 ambient)

Seems to work ok just wondering if the cycling thing is normal on these cars
 

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itguy08

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I did stick a digital thermometer in the air vent and it shows about 39 on the colder side and 42 on the high side. (55 ambient)

Seems to work ok just wondering if the cycling thing is normal on these cars
Probably normal at 55 degrees outside. That's not all that warm and the AC is getting to the cold point (39) very quickly. Try it again when it gets warmer, maybe in the 70s.
 

ahl395

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It is the compressor cycling on/off at the same intervals as the cold/colder temps. Seems to be the same idling or at speed. Base GT

I did stick a digital thermometer in the air vent and it shows about 39 on the colder side and 42 on the high side. (55 ambient)

Seems to work ok just wondering if the cycling thing is normal on these cars
I would agree with above. Try again when its warmer and it probably wont cycle on and off so often.

With a base however I didn't think it would as much since it doesnt go by cabin temp and you can just set the A/C on max. But still, I wouldn't worry until it gets warmer. If it gets warmer and does the same thing it may be low on freon.
 

HeelToeHero

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The cycling at idle is pretty normal. Have had a few cars do this.
 

TexasRebel

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I would agree with above. Try again when its warmer and it probably wont cycle on and off so often.

With a base however I didn't think it would as much since it doesnt go by cabin temp and you can just set the A/C on max. But still, I wouldn't worry until it gets warmer. If it gets warmer and does the same thing it may be low on freon.
The compressor cycling has nothing to do with cabin temperature. It is based on system pressures. With a lower ambient temperature the low side of the system will "freeze up" and restrict flow since the ambient air isn't adding as much heat into the evaporator. This restricted flow will raise the high-side temp and the compressor will shut off until the pressures go back to within operating range.
 

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Grinder67

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Update on this problem. It’s been in the 70’s-80’s here lately and the AC is still doing the same thing. It blows nice and cold for 15 sec’s, then cool for 15 sec’s, cold/cool, cold/cool. This is running down the freeway at 80mph. I took it to the dealer a week ago and they vacuumed the system and said it had the correct amount of Freon in it. Is this normal operation for this system? My wife’s new RAV4 blows cold all the time so this doesn’t seem right to me.

The interesting thing was they said they never heard of the evap problem on a Mustang. Actually 2 dealers in my area said the same thing.
 

itguy08

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Something is not right. We have also had those highs (finally) and my AC will blow cold until it cools down and then lower the fan a s warm up slightly.
 

TexasRebel

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Update on this problem. It’s been in the 70’s-80’s here lately and the AC is still doing the same thing. It blows nice and cold for 15 sec’s, then cool for 15 sec’s, cold/cool, cold/cool. This is running down the freeway at 80mph. I took it to the dealer a week ago and they vacuumed the system and said it had the correct amount of Freon in it. Is this normal operation for this system? My wife’s new RAV4 blows cold all the time so this doesn’t seem right to me.

The interesting thing was they said they never heard of the evap problem on a Mustang. Actually 2 dealers in my area said the same thing.
You need to find a dealer that knows how to check TSBs.
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