AC short cycles when in defrost.

[motorcyclist]

I noticed the other day that the defroster is not controling humidity good. found when defrost is on that the compressor short cycles just a split second on then off avout 15 sec. I can not find a low pressure switch on system, and cabin filter is clean and good air flow.I have worked on commercial refrigeration for 33 years, but not much on auto ac, although principals are the same. have not been able to check pressures due to I do not have automotive adaptors for my gauges. Does anyone have any idea as to what cycles the compressor on the fusion, as said before there is no visible low psi switch, only a high side one on the liquid line. Also when switched to AC it does the same. any ideas from anybody what causes this, vehicle has 34k miles so want to fix before the warrenty expires.

[akirby]

Classic symptom of low refrigerant.

[motorcyclist]

That is the first thing I thought of, however there appears to be no low pressure switch on the system, I followed the suction line the whole length and could not find one, only a high psi switch on the liquid line which is normally for safety in event of condenser fan failure, or possibly for condenser fan cycling.. It has been quite cold here below 40 deg, I am wondering if the compressor is cycled by temp, guess will have to pick up a set of automotive adaptors for my gauges to know for sure.

[cccerbeus]

depending on whether it is an orifice tube type or expansion valve type, the low pressure switch could be in a couple locations..

 

bottom line, as i'm sure you know, is that the only way to properly charge the system is evacuate and refill by charge weight.. since pressures are variable based on temperature and hi/lo port locations and system type

 

and yeah, definitely sounds like a low charge

[motorcyclist]

I think I found the problem. let it run a bit in driveway with ac on, liquid line gets very warm, and radiator fan will not come on causing it to trip on high pressure. bought a pair of harbor freight guages with adaptors (are pieces of crap, but ok for occasional use). head pressure goes up to aprox 275 and cuts off, suction goes down to 20 psi, but is cold today also so would run low suction.have appointment at dealer this next week before 3/36 warrenty expires.

Edited February 9, 2014 by motorcyclist

[Rok]

If it's going off on high head in the driveway, perhaps out on the road with air moving across the condenser, it'd correct some of the problem?

I believe if my Fusion's A/C ever were to have a similar problem, I'd not hesitate to evac and re-charge using R-12, labeling it appropriately.

Isn't the rule that you can re-charge using 134A once or twice on a system with known leakage but then have to completely evac and re-charge

the full refrigerant charge of 134A beyond that? I've heard that the different compounds could leak at different rates and repeated "topping off" of the charge creates a less effective compound in the system.

I already have the R-12 here. Like some of you, I did HVAC professionally for almost 30 years before retiring. Auto A/C is definitely a different animal.

Rok

[motorcyclist]

Regarding recharging with R12, that would depend on a couple things. first, if it has just a restrictor orafice and not a TXV, you would likely have an evaporator starving or flooding, where as a txv can compensate by throttling.I have run in to many instances where R12 was changed to another flavor on a cap tube system, it just dosn't work, one must install a txv which I have done many times and it works great. second, on R134A is not a blend so the mix will not get out of balance by topping off, however if one is topping off you must find the leak. some flavours like R404A which is not used in automotive is a blend and can become out of balance if has been topped off after several leaks.

[thefoeyouknow]

Use R-134a. I don't understand why this is even a question.

Regarding the topology of Fusion's A/C system, Fusion uses a TXV, and incorporates the receiver/dryer into the condenser in the form of a chambered desiccant cartridge. It's managed by the PCM who monitors an evaporator temp sensor to determine clutch cycling, and by the ACP sensor located in the high side which monitors the pressure there. The PCM will disengage based on both. It you're short cycling. your low on refrigerant. Period. What do you do? Add R-134A. It's cheap, it's available, and if you add it before your system goes dead, you'll probably get through the season. In the spring go see your A/C pro for leak diag. Usually, Fusion suffers condenser damage, but you'll want to verify this with UV dye. If you wan't to speed things up with your A/C pro, when you add gas, get gas that comes with a dye charge and charge it as liquid (with the system off).

[FusionDiffusion]

Are you sure the radiator fan isn't coming on? It's a variable speed fan so you probably won't be able to hear it when it is running on low. You need to visually confirm the fan is turning. If the radiator fan is the only problem, the A/C should work fine at speeds above 35 MPH because you have enough wind to cool the condenser.

 

Thefoe is right. Cycling is based on the evaporator temperature (shuts off when it gets down to 34ºF or something) and also the high pressure sensor you found. I believe the PCM uses the reading from the pressure sensor to control the fan speed (faster when the head pressure is higher) and will cut out the clutch if the pressure gets too high. Don't even think about R-12.

Edited February 13, 2014 by FusionDiffusion

[motorcyclist]

Use R-134a. I don't understand why this is even a question.

Regarding the topology of Fusion's A/C system, Fusion uses a TXV, and incorporates the receiver/dryer into the condenser in the form of a chambered desiccant cartridge. It's managed by the PCM who monitors an evaporator temp sensor to determine clutch cycling, and by the ACP sensor located in the high side which monitors the pressure there. The PCM will disengage based on both. It you're short cycling. your low on refrigerant. Period. What do you do? Add R-134A. It's cheap, it's available, and if you add it before your system goes dead, you'll probably get through the season. In the spring go see your A/C pro for leak diag. Usually, Fusion suffers condenser damage, but you'll want to verify this with UV dye. If you wan't to speed things up with your A/C pro, when you add gas, get gas that comes with a dye charge and charge it as liquid (with the system off).

normally I would think low gas, however 275 psi head pressure is way excess. on supermarket systems on 134A, you set the high safety around 250psi, plus being low on gas, normally your high side psi would be lower unless the system has non condensables (air) in it. As I said before I have worked commercial refrigeration for 33 years, but not much on auto systems, but my guess is the high side switch is used for high pressure safety only. also as for using R12 in this system I also can see no logic in doing so. refrigeration systems function best with the flavor it was designed to use.

Edited February 14, 2014 by motorcyclist

[motorcyclist]

Are you sure the radiator fan isn't coming on? It's a variable speed fan so you probably won't be able to hear it when it is running on low. You need to visually confirm the fan is turning. If the radiator fan is the only problem, the A/C should work fine at speeds above 35 MPH because you have enough wind to cool the condenser.

 

Thefoe is right. Cycling is based on the evaporator temperature (shuts off when it gets down to 34ºF or something) and also the high pressure sensor you found. I believe the PCM uses the reading from the pressure sensor to control the fan speed (faster when the head pressure is higher) and will cut out the clutch if the pressure gets too high. Don't even think about R-12.

Am positive, had gauges on watching head psi go up to at least 275 and liquid line very warm, fan never started.

[FusionDiffusion]

Am positive, had gauges on watching head psi go up to at least 275 and liquid line very warm, fan never started.

 

Alright, then that warrants further investigation. Check fuse #28 under the hood. If that is good, you may have a bad fan control module. With the key completely removed from the car, try turning the fan by hand to make sure it's not stuck.

Edited February 14, 2014 by FusionDiffusion

[thefoeyouknow]

What's your time to equalize? If you disconnect the ACP (pressure transducer in the high side), with the A/C on, after about a minute the fan (if it's any good) should spin up to 100%. Sounds like you're dealing with a hot condenser, though. Does your high side drop if you spray the condenser with a hose?

[motorcyclist]

What's your time to equalize? If you disconnect the ACP (pressure transducer in the high side), with the A/C on, after about a minute the fan (if it's any good) should spin up to 100%. Sounds like you're dealing with a hot condenser, though. Does your high side drop if you spray the condenser with a hose?

I just went out and tested it again, did not connect gauges, however it is a bit warmer this week about 50 deg. compressor cycles longer intervals, suction line cool, and liquid line cool to touch. the damdest thing condenser fan comes on now. tested the other day, was about 30 deg, fan must be controled by ambient temp. Problem is in cool weather can not get enough load to test accurately. Wanted to get checked as my warrenty runs out in 1800 miles, I might just remove charge and evacuate and fill with correct amount and see what it does. I see what you are talking about as in the cool weather the air discharge temp would drop fast causing to cycle on temp sensor, also in cool weather the suction psi would be much lower also. not being an auto tech,I assumed that the switch on the high side was only a safety, is it actually a transducer instead of just a switch?

Edited February 14, 2014 by motorcyclist

[FusionDiffusion]

Yes, it is a pressure transducer. If you use a scan tool you can see the readout in psi or kPa. Yes, there are multiple temperatures and pressures that play into whether the fan will come on and at what speed. Also note that below a certain outdoor ambient temp the compressor will no long run.

[motorcyclist]

Yes, it is a pressure transducer. If you use a scan tool you can see the readout in psi or kPa. Yes, there are multiple temperatures and pressures that play into whether the fan will come on and at what speed. Also note that below a certain outdoor ambient temp the compressor will no long run.

Do you know if this has a low psi switch or transducer, I can not find one anywhere on the suction line, is not on compressor, would not think it would be located on the evap, however have seen some stranger things. I think I will recover the gas and weigh in correct charge just to satisfy curiosity.

[FusionDiffusion]

There is no low pressure switch or transducer. Just the high pressure transducer. The reason it doesn't have a low switch is because it uses the evaporator temperature sensor instead (the most direct way to control compressor cycling). Remember the point of having a low pressure switch is to prevent evaporator freezing, so directly measuring evaporator temp makes a low pressure switch unnecessary.

[motorcyclist]

There is no low pressure switch or transducer. Just the high pressure transducer. The reason it doesn't have a low switch is because it uses the evaporator temperature sensor instead (the most direct way to control compressor cycling). Remember the point of having a low pressure switch is to prevent evaporator freezing, so directly measuring evaporator temp makes a low pressure switch unnecessary.

I did not think that there was. seems it should have one for a safety in the event of a refrigerant loss so as the compressor would not keep running without refrigerant, unless the high side control would lock it out in that event.