Motor Vehicle Maintenance & Repair Asked on December 23, 2020
I have a 14 plate Fiesta – the air conditioner in the car seems to be linked to the main air intake so if you turn the aircon on it sounds like the fan is working really hard (which I guess is because it is).
Anyway, yesterday I noticed that when I turn the engine off there is this low rumbling vibration – it sounds like there is a large truck passing you and making the ground rumble. I tested it twice today, one half of the journey I had the A/C on then pulled over and turned the engine off and it rumbled, then I did the rest of the journey with the A/C off and when I turned it off, no rumble.
Weirdly if I turn the engine back on and wait for about 2 or 3 mins with the A/C on then turn it off there is no rumble so it seems to be with the A/C on with the engine running for a while?
I have noticed that the air hasn’t been really cold over the past few weeks and interestingly thought I should run it in for a re-gas. Would a lack of gas cause this shudder / rumbling noise?
A/c condencer fan may be faulty When its speed decreased to stop Due to turn off ignition
Answered by user32558 on December 23, 2020
A clutch equipped AC compressor like the one on your car isn't pumping whenever the engine or the AC system is off (and, most importantly, whenever the clutch coil isn't engaged so that the clutch hub isn't rotating).
The system equalizes when turned off, that is, refrigerant where the compressor once kept a high pressure starts migrating wherever the pressure is lower once the compressor is turned on. All of this unless the system features a liquid line solenoid valve that closes once the compressor turns off, which small AC systems such as car ones usually don't feature.
The noise you hear might just be the AC system equalizing.
A properly done AC system check, evacuation, vacuum and recharge cycle, especially if you ask the AC professional how much refrigerant has been pulled from the system, would surely do good to the AC system, and it may also help pinpoint any eventual leak. In addition, the compressor's oil usually comes diluted with a dye that shines whenever it's exposed to blacklight.
Answered by Al_ on December 23, 2020
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