A/C Evap core freezing and hissing noise

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Midnight_rex

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I have a 2011 1500 with a 4.7L. I replaced my evaporator core a couple years ago due to a leak and also replaced the expansion valve. After a good vacuum and recharge the AC worked good up until recently.

There has been a hissing sound coming from the passenger side underneath the glove box area when the AC is turned on. It happens when im in higher RPM while driving for about 5 seconds and then fades away. Also, after driving for about 20-30 minutes air from the vents start to blow weak but still cold. It gets to the point where i have to turn the AC off because the evaporator core freezes and i would have to let it defrost.

a couple of weeks ago i pulled a vacuum for about 1 hour and half and recharged it to factory specs. Its still doing the same thing. Am i not putting enough freon in the system? Im measuring with a small weight scale as im filling the system.

Could filling the system with a lil more freon fix this issue? Yes i have a set of manifold gauges and a good vacuum pump. Any suggestions could help. Thanks.
 

crash68

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if your weighing in the factory charge amount and the AC is still freezing up, there is most likely another problem. Adding extra refrigerant will only create more problems, it's not a case of more is better.
It's possible the evaporator is dirty/plugged or the metering device has gone bad. You an buy lighted bore cameras for cheap on Amazon that plug into smart phones. Pull the blower motor and look at the face of the coil(s).
One tip for a more accurate weigh in of the refrigerant is if your scale can measure in grams.
 

SeppW

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Frankly, there's a lot going on with AC and unless trained, I wouldn't even attempt to diagnose it, let alone fix it. Once the system has been opened introduces all sorts of new issues. A major repair such as a core replacement usually requires the replacement of the other major items in the circuit, e.g. condenser, compressor, drier, expansion (or orifice), lines flushed, seals replaced, oil replaced, refrigerant recovery, and proper charge, but rarely gets done. Freezing core could be low refrigerant, bad or clogged expansion valve, or clogged orifice. Since you said you replaced expansion valve, I assume it's an expansion valve system. Did you replace the drier as well? Does the expansion valve freeze up too? When you pulled the vacuum, was their any leak down detected on the gauge after shutting off vacuum pump?
 
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Midnight_rex

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Frankly, there's a lot going on with AC and unless trained, I wouldn't even attempt to diagnose it, let alone fix it. Once the system has been opened introduces all sorts of new issues. A major repair such as a core replacement usually requires the replacement of the other major items in the circuit, e.g. condenser, compressor, drier, expansion (or orifice), lines flushed, seals replaced, oil replaced, refrigerant recovery, and proper charge, but rarely gets done. Freezing core could be low refrigerant, bad or clogged expansion valve, or clogged orifice. Since you said you replaced expansion valve, I assume it's an expansion valve system. Did you replace the drier as well? Does the expansion valve freeze up too? When you pulled the vacuum, was their any leak down detected on the gauge after shutting off vacuum pump?
No i did not replace the drier. The drier is integrated in the condenser which means i would have to replace the whole condenser. When i pulled the vacuum there was no leak down. It stayed in vacuum for 1 hour. I havent got to check if the expansion valve is stuck.

The ac system isnt that hard to understand. Even certified techs dont replace every component in the system when something goes bad. I never experienced these 2 symptoms before so i thought someone would have a good idea what it is.

There are no leaks in the system and im sure of that. The AC blows cold when the core doesnt freeze. There have been mutiple times where the core doesnt freeze and the AC runs good. But now it freezes more often.
 

Daw14

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Sounds like it’s low on refrigerant and that is causing it to freeze up. Your charge needs adjusting.
 
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Midnight_rex

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So i just checked to see if the expansion valve is sticking and its not. When i turn off the AC, both the low and the high side equalize. I checked low side pressure while AC on and it reads 35psi. The AC compressor is cying on and off like it should. I added a little more freon and low pressure was left a little of 35psi.

i also noticed that the electric fan is not turning on. I checked the fuses and found that fuse J12 was blown out whoch is labeled “rear AC fan etc.” I replaced with another 30amp fuse with no luck of fan turning on. Looks like i have a electric fan that i need to replace now.
 

Tach_tech

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What’s your high side pressure reading?

If the fan isn’t working it can cause a pressure increase which can cause the evaporator to freeze up.
 

SeppW

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So what are the static pressures relevant to ambient temps? What are the running system pressures relevant to ambient temps? If the high side was 100 psi, and not knowing the ambient temp at your location, I'd say that is too low. Low pressure, stated 35 psi, is the ball park.
 
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Midnight_rex

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So what are the static pressures relevant to ambient temps? What are the running system pressures relevant to ambient temps? If the high side was 100 psi, and not knowing the ambient temp at your location, I'd say that is too low. Low pressure, stated 35 psi, is the ball park.
So for ambient temperature (atmospheric temperature)= 90F the high side will need to be ~250-270psi and low side ~45-55psi

i guess there is a restriction which is why you are asking about static pressure as a definition in liquid/gas? Or are you referring to airflow for HVAC terms? Cause there is different types of static pressures to go by.

anyways, the whole time while the AC was on and i had the manifold hooked up to the system, the high side never seemed to reach above 200psi. I will have to check again tomorrow and see for sure as i will have more time to diagnose.
 

SeppW

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So for ambient temperature (atmospheric temperature)= 90F the high side will need to be ~250-270psi and low side ~45-55psi

i guess there is a restriction which is why you are asking about static pressure as a definition in liquid/gas? Or are you referring to airflow for HVAC terms? Cause there is different types of static pressures to go by.

anyways, the whole time while the AC was on and i had the manifold hooked up to the system, the high side never seemed to reach above 200psi. I will have to check again tomorrow and see for sure as i will have more time to diagnose.
Trying to narrow it down. Static to determine if refrigerant pressure is equalized. If not then determine if low or overcharged.
 

Tach_tech

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Static pressure is with the system at rest and both high/low should be equal.

If the low side pressure was around 30 which is slightly low with a high side pressure of only 100, which is very low. I would be leaning towards low charge, there’s a restriction in the evaporator or you’re compressor is on its way out.
 

crash68

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If the head and suction pressures are low, check how much sub-cooling guessing it's high. If that's the case then it's the metering device or low load as in a restricted coil (air or refrigerant).
 
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