A/C is cold until the fan is on high, then it's warm

When the a/c fan is on any setting other than the highest setting the air comes out cold. When the fan is set to the highest setting, it only comes out warm. This happens regardless of a/c or max a/c setting, regardless of fresh or recirculated air, and regardless of car speed. (2005 Mustang GT)

First, determine if it’s the A/C clutch kicking out when the fan is switched to high.

It could be the blending door. Somehow on high setting it’s blocking off AC.

Gotta be low system charge. U could check pressures, but I say evac and recharge with proper fill. Bet it works fine than. U are probably used to <great performance from a/c. Riding in a car with good a/c might surprise u.

I checked the compressor and it is cycling on and off every few seconds in all scenarios. If it needed a recharge wouldn’t that mean it should only be blowing warm air? The fact that the air is still cold (at low fan speeds) but the compressor cycles on and off rapidly confuses me. Are those typical characteristics of a low charge or something else?

Temp at driver vent, max ac, should be around 40-45. Do you have this at low fan speeds?

Air can feel cold even with a low charge causing short cycles.

I got out my thermometer and took some measurements at the driver’s side vent. (It’s 75F outside) On all settings other than high I get 66F at the vent, that’s with normal & max a/c and fresh & recirculated air. Turn the fan on high and it goes up to ambient temperature (also regardless of norm & max, fresh & recirc).
Obviously not as cold as it should be, I just thought I wouldn’t get any cold air at all if it needed charging.

When the compressor cycles on and off every few seconds, that is a symptom that the system needs to be recharged. When the blower is on high speed, the system can’t cool the higher volume of air.

The poor cooling performance and rapid cycling of the compressor clutch is vary likely due to a very low charge level. The system won’t be completely disabled until there is no pressure detected in the system (less than 25 PSI), in the mean time the compressor can be damaged by operating undercharged due to poor lubricant circulation.

An AC system has a max flow rate that it can fully cool the air. At a certain air flow rate the AC can’t keep up, and the air that does come out then will be warmer than at lower flow rates. My guess is your AC system isn’t working at the capacity it did when new, and as posted above by the experts here, the charge level is probably the first place to look.

My car (2014 Nissan Sentra) is doing the exact same thing and i went to Firestone and they charged the system but still AC is behaving the same. Now they are asking me to replace the entire AC system. Any suggestions.

PS: there are no leaks in the system

You’ll get better results here by reposting with all the pertinent details as a new topic. Click “maintenance/repairs”, then “new topic”.

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First thing to do is STOP GOING TO FIRESTONE or any other national chain. Find a good independent. Best is one that specializes in AC systems.


So if there are no leaks in the Nissan then why did they charge the system? And it is unlikely the entire system needs to be replaced.

There are 2 things you need to do. Avoid Firestone and find a good A/C specialty shop.
With A/C problems it is near impossible to offer advice without knowing both low/high side pressure both at idle and elevated RPMs along with a few other questions. Odds are at 8 years old; low charge.

In regard to the Mustang in the original post I might point out how off base someone’s opinion of “cold” is.
Ambient is mid 70s and they think 66 is cold. The compressor cycling on/off rapidly and lousy performance means it’s very low on refrigerant; and likely needs a leak or two fixed at 11 years of age.