Replacement AC compressor short-cycling

[davel]

I bought a 2017 V6 from Carmax. Four months into owning it the AC compressor seized, damaging the serpentine belt. Both were replaced at a Carmax approved. Independent shop. When I first picked up the car, the AC system would cycle on and off at idle every two minutes or so. This seemed kind of odd to me, but I didn’t know whether it was normal or not for this car. Fast forward four months, and the system was cycling on and off at idle every 15 seconds. This was right before the compressor failed. The replacement compressor that’s in the car now is starting to do the same thing. Sometimes at idle it cycles every 10 seconds. I’ve read old posts on this forum about early sixth generation cars having evaporator core problems, I’m wondering if that’s what’s going on here. I have an appointment to bring the car back to the independent shop that replaced the compressor. They guarantee their work, but I’m not sure what that would mean in this case. I’m wondering what kind of conversation I’m going to have to have with the service manager there about this issue. It’s my assumption that the Carmax warranty will pay for replacement of a defective evaporator core. Apparently, this job is a huge pain in the butt. I’m wondering if the shop might be reluctant to do it.

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[horsepower addiction]

They should have changed the compressor, flushed the system, changed the orifice tube or expansion valve whichever one you have, change the dryer. With it cycling every few seconds it is probably leaking Freon. Is it blowing warm?

 

[Basspro302]

I bought a 2017 V6 from Carmax. Four months into owning it the AC compressor seized, damaging the serpentine belt. Both were replaced at a Carmax approved. Independent shop. When I first picked up the car, the AC system would cycle on and off at idle every two minutes or so. This seemed kind of odd to me, but I didn’t know whether it was normal or not for this car. Fast forward four months, and the system was cycling on and off at idle every 15 seconds. This was right before the compressor failed. The replacement compressor that’s in the car now is starting to do the same thing. Sometimes at idle it cycles every 10 seconds. I’ve read old posts on this forum about early sixth generation cars having evaporator core problems, I’m wondering if that’s what’s going on here. I have an appointment to bring the car back to the independent shop that replaced the compressor. They guarantee their work, but I’m not sure what that would mean in this case. I’m wondering what kind of conversation I’m going to have to have with the service manager there about this issue. It’s my assumption that the Carmax warranty will pay for replacement of a defective evaporator core. Apparently, this job is a huge pain in the butt. I’m wondering if the shop might be reluctant to do it.

You can call them or drive up and ask them.

 

[davel]

They should have changed the compressor, flushed the system, changed the orifice tube or expansion valve whichever one you have, change the dryer. With it cycling every few seconds it is probably leaking Freon. Is it blowing warm?

They flushed the system but didn't replace anything but the compressor. I don't think the Freon is leaking, it blows as cold as ever. But that's what happened with the previous compressor, it worked fine until it didn't, then it imploded. I'm taking the car back to the shop tomorrow.

 

[Roadsign]

As mentioned already, if the compressor has failed the evap core and lines can be flushed, pretty much everything else will need to be replaced. Debris from the compressor can not be fully cleaned from the other components so they need to be change or there is high probability for future compressor failures.

 

[SCP440]

It could be switching off because its going over pressure and then switching back on when the pressure drops. Did they put the correct amount of Freon in ?
Is the fan cutting in to keep the condensor cool ? I dont know if its supposed to run all the time with the A/C on but a correctly functioning cooling fan is critical to the system working properly.
A decent scan tool should be able to monitor the system so you can see what is causing the compressor to cut in and out.

 

[davel]

Six weeks ago when the compressor failed they replaced the compressor and the expansion valve and the damaged serpentine belt and flushed the system. I brought it back to the shop today cause it’s short cycling. They admit that it might be short cycling, but said the system has not leaked any refrigerant in six weeks so it’s not a leak problem. It seems like what they’re telling me is to drive it around while it’s short cycling and wait for the compressor to fail again and then they will do whatever necessary repairs at that time. Needless to say, I would prefer to do the repairs when it’s convenient for me and not just wait for it to fail at a time or place that is potentially very inconvenient and have to drive around with a damaged serpentine belt.

 

[Skye]

I think we all agree cycling every 10 seconds indicates a problem. The shop that did the work has a warranty period. It might be they're hoping nothing else happens until that time has expired.

My perception is the 6G cars aren't any more vulnerable to evap core or other parts failures than any other manufacturer, with the exception of the GT350s. We've had a few report several failures involving the same line/joint, the belief being the vibration of the engine and the quality (poor) of the joint causes those lines to fail. Mustang-wide though, I think we're average with other models. YMMV.

The cycling of the compressor could be caused by low refrigerant. But it could also be caused by a blockage in the system.

Once compressed and cooled by the condenser (the high side), the liquid should then go to the evaporator core inside the interior, where it expands, absorbing heat in the process (the low side) and cooling the occupants.

If there was prior damage and debris has been allowed to condense and plug part of the assembly, it would restrict or outright prevent gas from the low side returning toward the compressor to start the process again. This could explain the cycling compressor. It acts like it's low. It is. Not because of a leak, but because enough of the refrigerant can't get back fast enough to be compressed again.

In my scenario, the same gauges indicating the amount of refrigerant in the system should also indicate it is not flowing correctly.

- Low/no refrigerant
- Restriction/blockage
- A faulty pressure switch
- Something else

To the radiator fans, those should come on as soon as the A/C system is turned on. They'll run at their low-speed setting to draw air across the condenser and should stay on as long as the A/C is turned on. If the engine coolant is warm enough, like sitting in traffic, the fans can spin at high speed. The radiator fans should be on or off, but not cycle, if that makes sense. A/C switch on, compressor cycling, fans should be on full-time, until the A/C switch is turned off by the driver.

Sometimes we have Members whose cars are not repaired well by other shops, like a body shop. The insurer then gives them an option of seeing another facility. I'm unfamiliar with whatever agreements CarMax might have with any shop, but I'd start with CarMax. Call and explain the events and why you'd like to try another place. You'd like a new shop to study the problem with a fresh pair of eyes.

Hopefully, CarMax gives you another referral. CarMax has a warranty, but let's face it, they're going to want to keep their costs down and not necessarily select the most qualified shops. Maybe a second chance at another shop could help.

An alternative involves you spending some money out-of-pocket, to have the current problem diagnosed by another shop, preferably a Ford dealer. IDK if Ford dealers have a flat fee. Many independent shops often charge an hour labor to do a review and provide thoughts and estimates. Doing something like this before re-engaging CarMax could be helpful.

No answers, but some additional ideas on how to attack the problem.

Good Luck.

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