Hi everyone,
I have a 2016 V8 Vantage S with 26k miles. Today on my way home from getting coffee, the A/C (Set to low temp) started working intermittently. Thought it was just a coincidence. Took it out about 30 min ago and the AC is not working anymore, only blows warm air. At the same time, my radiator fan is running at full speed and sounds like a jet engine despite the temp gauge indicating towards the middle. I'm lost as I don't know what could cause these two to happen simultaneously. Any ideas?

I'm going to check the coolant levels once the engine isn't hor.

 

There is an intimate relationship between fan speeds and the kPa of the AC output.

Fan speeds are controlled/managed by the ECM and it uses ECTs to determine fan speed (as a percentage) based on a given coolant temp. However, if the AC is turned on, then the ECM switches tables to use the kPa of the AC output. So, if AC is suddenly switched off, the ECM switches control of fan speed to ECT.

As a tuner I see these data tables in the EMS. The tables I will show here are not your car, per se, however, typical.

Fan speed controlled based on AC kPa output:




If the AC is shut off, then the ECM reverts to ECTs:




Fan speeds are never 100% (that I have ever seen). 90% is the highest programmed speed.

My suggestion to you (and what I suspect happened) you lost AC. Could be myriad reasons, the ECM switched automatically to ECTs. With ECTs, the highest fan speeds are reached sooner than when AC is on which might explain what you heard. Be weary of dash temp gauges as, often, these gauges are not linear. Very common on circa Astons, Jaguars, LRs. Some of these still make temp gauges to read "half way" until serious overheat, then the gauge pegs.

Figure out what happened to your AC and the fans will return to normal (a normal sound to your ears, but what you heard is also normal fan speed) is my prediction.

 

Thank you for the information! I'm definitely going to take a look at that and see what issue my AC might have developed.

Quick question, I read on some old post that the coolant temperature sensor could have gone bad and can cause the A/C to be loadshed by the car, does this sound like a possibility to you? I am planning on taking it in next week but trying to see what I can do on my part in the meantime.

 

Also check the exterior temperature sensor. What does it read on your dash?

 

That's a good one too, it's reading 32 Celsius in my garage, used a thermometer and it is pretty accurate. I almost thought that was the solution because I used to have a bmw 335i and its ambient temp sensor went bad, and it also had a ton of issues as a result. I'm going to take another look tomorrow and see if it remains accurate.

 

I am not that good with ACs. Something stopped the compressor. Could be sensors, could be the drive belt, could be a refrigerant leak. All things to check. Good news is lots of indies can diagnose/repair ACs so you should have options to an AM dealer.

All the Best!

 

Thank you! Yeah it seems like it should be an easy fix, it'll be going in for service next week.