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Weird A/C issues

alawadhi3000 on Wed July 17, 2013 4:08 PM User is offline

Year: 2004
Make: Hyundai
Model: Coupe/Tiburon
Engine Size: 2.7L
Refrigerant Type: R-134a
Ambient Temp: 35C/95F
Pressure Low: 25
Pressure High: 150
Country of Origin: Korea, Republic of


I've had nothing but issues with my car's A/C over the last few years, I'll try to describe them as best as possible.

Last year symptoms:-
Compressor will cycle on and off if the low side pressure was more than 45psi on a 42C/108F humid day, the A/C shop told me that at these temps/humidity the pressure should be around 50psi.
Vent temp at idle is barely cold (about 70F if I remember correctly).
If I rev the car to ~1500rpm, the vent temp gets way colder to like 50F.
If I'm idling, whenever I press the accelerator more than say %30 the compressor will turns off and then runs again after like two seconds.
System was put on a vacuum test for a few hours by the shop and he told me that there are no leaks and he is suspecting problems with the expansion valve.
I noticed that when its about 30C/85F at night, the vent temp is cold enough, when I rev it to ~1500rpm the vent temps go down slowly to about 5C/40F and then the compressor shuts off for like a minute and vent temps go to like 65F-70F before the compressor kicks on again.

This year:-
Compressor will cycle on and off if the low side pressure was more than 25psi on a 40C/105F humid day, yet again, no leaks, and it seems that the compressor cycling is affected by the weather, if the outside temps are lower the compressor will take a bit more refrigerant before going crazy.
Vent temps are a bit worse than last year.
The A/C shop technician told me that my high side is getting a bit hotter than it should, indicating that there's an obstruction on the high side lines.

Radiator is a few month old and works perfectly.
Both radiator fan and A/C fan work perfectly.
A/C performance is nearly the same whether I'm stopped or moving, the vent temp is depends on the RPM.

I'm just a college boy so I'd appreciate it if I get an expert opinion before burning more cash trying to fix the system. Thanks.

mk378 on Wed July 17, 2013 4:17 PM User is offline

The first step is to recover the refrigerant, evacuate, and recharge by weight to the manufacturer's specification. The symptoms between last year and this year are consistent with leaking out. High side line will get very hot when you run a TXV system low on refrigerant.

alawadhi3000 on Wed July 17, 2013 4:21 PM User is offline

Thanks for the reply, I forgot to mention that last year the shop already did what you asked to, these symptoms were after that.

alawadhi3000 on Thu July 18, 2013 9:19 PM User is offline


Olds442 on Sat July 20, 2013 3:27 PM User is offline

It sounds like you may still be undercharged. Put a few more ounces of 134 in and see if it improves. At that ambient your high pressure should be higher than that.

alawadhi3000 on Sat July 20, 2013 4:58 PM User is offline

The problem is if I put anymore refrigerant in it the compressor will begin to cycle on and off rapidly, same thing when the system is overcharged.

Olds442 on Sun July 21, 2013 2:27 AM User is offline

Fast cycling is usually a symptom of undercharge. An overcharged system hardly cycles at all . . . if all else is right with the system.

alawadhi3000 on Sun July 21, 2013 7:03 AM User is offline

We topped of the refrigerant to 45PSI on the low side, which should be fine for a 40C/105F weather, the A/C worked fine when it was idle for about 10 minutes but the moment I started driving I heard a sound like a tire being delfated and the compressor started rapid cycling.

So I went back to the shop and took off the refrigerant 5PSI at a time until the rapid cycling went away @ 25PSI, but the A/C now is not that cold especially at idle.

mk378 on Sun July 21, 2013 8:19 AM User is offline

Does the condenser fan work? The sound of refrigerant escaping means there was a severe overpressure on the high side, which opened the relief valve.

Guessing at the charge level by pressure (especially just low side pressure, are you even looking at the high side???) is almost a guarantee of poor results. The manufacturer spent considerable effort to determine the proper charge by weight and have the factory weigh that charge into every new car. Charge it by weight and be done guessing about the charge. If it doesn't work when properly charged by weight, troubleshoot what else is wrong.

Edited: Sun July 21, 2013 at 8:20 AM by mk378

alawadhi3000 on Sun July 21, 2013 12:41 PM User is offline

Yes condenser fan works perfectly, the shop even splashed the condenser with water (and nearly killed my crackshaft sensor) and it's still the same.

I'll go to the shop hopefully tomorrow and I'll get the readings for both the low and high sides. As for recharging the system what would you suggest? Do I need to completely discharge the system and then put a new refrigerant by weight?? Thanks.

Olds442 on Mon July 22, 2013 3:36 AM User is offline

Yes, empty it and recharge to the prescribed weight of refrigerant. You can't get an accurate charge by PSI.

iceman2555 on Mon July 22, 2013 9:26 AM User is offlineView users profile

Rapid cycling does not always mean a 'undercharged' system. A restriction in the system that elevates high side pressures sufficient to engage the HPCO will result in cycling also.

There are several issues at play at this point...first and foremost is the 'topping off'. A modern AC system lacks the ability to be serviced in this manner. The charge rates are so small that the systems can not absorb the possible extra amount of refrigerant that may be added to the system. It is essential that the systems be recovered, evac'd and recharged to OE specification. There is no way a DIY'er is going to properly recharge a system utilizing small cans....or attempting to charge by pressures.

Watched a 'counter person turned AC pro' recently attempting to recharge a customers car in the parking lot of a major auto parts retailer. Guess he bought into the commercial....use AC Pro and become a PRO...yeah right...any way...there were two cans of this product near the vehicle. One sitting on the ground and the other in the hands of this newly certified AC pro. He simply could not get the evap to cool....add some cooling....add some more....rapid cooling....add additional amount.....over and over, as I watched.....transfixed at this spectacle....finally could not longer stand by.....conducted a few preliminary test....the old method....touch lines...visually check the system.....something a true AC PRO would know....discovered that the fan clutch was not condenser cooling....resulting in severe high side temps/pressures.....highly elevated inlet temps will reduce evap temps....the cycling was the result of the HPCO simply protecting the system.

To simply state the is essential that the systems be properly charged prior to performing a performance diagnostic procedure.

There are several comments that point to a restriction within the high side. When the system is charged to what appears to be the norm the cycling begins and also when the RPM is increase, there is a sound similar to 'air being vented from a tire' indicates that the Pressure Relief Valve (POPOFF VALVE) is working. This unit has a PRV valve located in the compressor manifold. It is also possible that the system has a redundant HPCO located in the system also. The statement that the 'high side line' was hotter than normal. This could be an indicator of a condenser inlet restriction.

The compressor utilized on this vehicle is the Ford HS15. The new member of the FS10 family. These are know for producing debris when the system is undercharged. This could be the result of loss of refrigerant over a period of time.

First insure...forget the adding/subtracting of refrigerant.....have the system properly serviced by someone that has the correct equipment. This is the only method to determine the charge rate. At this point pressures and operational temperatures become valid. Test pressures under high heat loads (Idle, Max Cool, Doors Open, High blower) compare pressures and vent temps at this point. Seek a vent temp drop of app. 30 degrees between ambient temp and center vent. IE. 95 outside....60 degree vent. May vary a bit either side. Should not cycle. Second test....Low Heat Load...(Max Cool, Med Blower speed, Doors CLOSED, engine rpm 1200-1500 stable). Compare pressures/temps at this time. Vent should become cooler and compressor cycling should occur if blower speed is reduced to Low and system has had opportunity to cool the cabin.

Test temperature of the condenser inlet (Discharge line) compressor to condenser. If line is too hot to touch and the PRV is being activated the condenser is restricted. This condition may not be evident if the high side pressure port is located on the liquid side of the condenser.

Let us know the results.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Cussboy on Mon July 22, 2013 12:13 PM User is offline

Originally posted by: iceman2555
Watched a 'counter person turned AC pro' recently ...

I like to hear the guys at the auto parts stores claim they "used to be" mechanics. Of course I then wonder why they "chose" to take counter jobs paying at most half as much???

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