Automotive Air Conditioning Information Forum

Hello!

I'm having some issues with the AC in my 2014 Mitsubishi Outlander Sport. The AC blows fine and cold when it's on full blast whether driving or idling, but as soon as I drop it lower than full blast, the AC compressor starts to short cycle. It will kick on for about 5-10 seconds, then turn off, then after about 5-10 seconds turn back on, etc.. the pressures when the compressor is on are: Low side: 28-30 psi, High side: 170 psi. Ambient temperature is 74F. After pressures equalize with the car off, they're both at 116 psi. Does anyone have any thoughts of what the issue could be?

Thanks!

At that ambient temperature, it sounds to me like the system is operating normally, cycling the compressor to prevent the evaporator from icing up and blocking airflow at the lower blower speeds. The pressures look good as well. What center vent temperatures are you seeing?

Thanks for replying! So at idle at full blast, the temp is at 45.7F. When idling and at half speed, the temp will drop to 41.4, the compressor will cycle off, the temp will rise to 43.6 and then cycle back on. All within about 10 seconds, going back and forth constantly. I know the temps and everything seem fine and consistent for the most part, but from my understanding, isn't it not good for the compressor to be cycling on and off that fast?

Thanks!

Do you know whether the A/C system has ever been serviced and what was done? If not, it's possible that a small amount of refrigerant has leaked out over the years due to normal seasonal losses from the front shaft seal. That, coupled with the small-displacement scroll compressor that I believe your car has, could result in a bit more cycling compared to when the car was new. I don't think the cycling will hurt anything, though, because the system is designed to do that in order to keep the evaporator temperature just above freezing.

If you really would like to know whether the system is a little low on refrigerant, you could take it to a reputable A/C shop, have them recover the charge, and weigh it. That'll tell you for sure. If it is low, then have them evacuate and recharge it to factory specs: 18 ounces net weight of R-134a and 2.4 fluid ounces of PAG-46, or whatever the under-hood decal says.

Even though vent temps and pressures are typically measured at 1,800 RPM and not at idle, it appears that your A/C system is cooling pretty well right now. If you're not in the Southwest, I think I would just leave it alone until next season when ambient temperatures rise to 80 degrees or higher and then see how it performs. You might not have to touch it at all.

Thanks! Unfortunately I'm not really sure about prior maintenance as we just purchased it about a month ago from a dealer.

I do live in Arizona, so it does still get decently warm during the late afternoon. So I can test it a bit more when the ambient is a bit warmer.

As far as I can tell it doesn't short cycle while driving, just at idle. Which, unfortunately with small kids and not wanting to haul all of them in to every place we go, happens frequently while one of us runs in.

I appreciate your feedback! I'll check again when it's warmer later in the day And see if anything changes drastically.

Check pressure at idle and also 1500 RPM. We are not going to be warm much longer. Well, at least for a few months.

If possible, recover and chargeback to Spec.

Nighthawk501 wrote: ↑Thu Oct 28, 2021 5:17 pm As far as I can tell it doesn't short cycle while driving, just at idle. Which, unfortunately with small kids and not wanting to haul all of them in to every place we go, happens frequently while one of us runs in.

Not sure that I'm clear on this. Does it not cool very much at idle or is the cycling at idle the only issue that you've noticed?

I read it as at Idle.

I would always get a baseline on the refrigerant, and fan concerns would be starters for me.

JohnHere wrote: ↑Fri Oct 29, 2021 8:59 am

Nighthawk501 wrote: ↑Thu Oct 28, 2021 5:17 pm As far as I can tell it doesn't short cycle while driving, just at idle. Which, unfortunately with small kids and not wanting to haul all of them in to every place we go, happens frequently while one of us runs in.

Not sure that I'm clear on this. Does it not cool very much at idle or is the cycling at idle the only issue that you've noticed?

It cools fine at idle, really just the cycling at idle is the only issue I've noticed.

Okay, it sounds like it's cooling the way it should.

Since we don't have any A/C service records for reference, it might have lost a little refrigerant over the years, as said before, but not enough to affect cooling yet...just that it cycles more frequently at idle.

If it were mine, I would recover, weigh, evacuate, and recharge to specs. At least then you'd know that the system has the correct charge. Verify that the fan(s) are running at full speed at idle and/or 1,800 RPM with the compressor engaged...two important earlier suggestions.

It's also important to avoid introducing any sealer or other additives into the system. Pure R-134a only.