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Hey everyone, I lost my AC last Sunday and have been doing my research in order to solve my problem. I noticed a lot of people have intermittent issues and replacing the thermal control amplifier, but I don't think that is my problem. Just as a precaution though, I already bought a replacement to take care of that issue before it happens. I would appreciate everyone's opinions and help to get my truck from baking in this GA heat.

Here's what I know and the symptoms associated with my problem.

A/C is completely gone.
All fan speeds work.
Temp control blows warm air on COLDEST setting, and hot air on HOTTEST setting.
The A/C button clicks the relay and I can hear the compressor clutch kick in as well.
Before the A/C went out, I could hear a hissing sound from behind the HVAC controls on and off every 30 seconds or so(I'm assuming due to the vacuum system), and now it constantly hisses. I have already checked for a leak behind these controls to no avail.
The upper A/C hose has a small leak, while the lower hose has a small/medium leak. Now keep in mind, there hasn't been a slow decline in temperature at all. Just ON then completely OFF. I will be replacing these hoses. There seems to be a full charge in the system.

I might have missed some other information, but that is the majority of what I know. If there is any ideas or assumptions I need to add, let me know!

Can anyone bless me with their knowledge? Thank you.
 

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If you have 2 leaking lines, those may be the problem. Most cars have a low pressure shutoff when the refrigerant is low. It will still have a charge, just not enough.

Hook up some gauges and see what the charge actually is. That will help more than anything. You have to know what the low side and the high side are doing in unison. Using the single gauge on the refill can's wont work... although if you hook it up and it over-pressurizes and breaks the gauge, the compressor is shot.
 

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Discussion Starter #3
If you have 2 leaking lines, those may be the problem. Most cars have a low pressure shutoff when the refrigerant is low. It will still have a charge, just not enough.



Hook up some gauges and see what the charge actually is. That will help more than anything. You have to know what the low side and the high side are doing in unison. Using the single gauge on the refill can's wont work... although if you hook it up and it over-pressurizes and breaks the gauge, the compressor is shot.


So I just had my system evacuated so I can replace the hoses and the machine said my static pressures were just fine. My only saving grace for a solution was just eliminated. I'll be replacing the hoses and thermo control amp today and hopefully get the system recharged.

Any other ideas would be appreciated haha.


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So I just had my system evacuated so I can replace the hoses ... I'll be replacing the hoses and thermo control amp today and hopefully get the system recharged.
That's a decent plan. ALWAYS fix First what you KNOW is bad.

Sorry, but if you had leaky hoses, then you DID lose some refrigerant. The fact that your static pressure reads OK is not meaningful here, a small amount or full charge of R134a will have the SAME static pressure. And if that static pressure was below spec then the AC compressor would not engage due to the pressure switch protecting the system.

My mechanic said that AC hose leaks are common on these trucks (even though I have not yet experienced that on my 2 Frontiers or my daughter's 1998 Pathfinder). So I suspect that replacing the AC lines, having the system evacuated, and correct amount of R134a added by weight will take care of your issues. I've read where 70% of AC issues are due to loss of refrigerant.

In your case - where the system should be "open" for only a few minutes while changing the lines, and has not been empty of refrigerant - I might not even replace the drier.
 

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A small amount of refrigerant compared to a full charge will not have the same static charge; it will be lower. Static charge will vary slightly with temperature, but you'll typically see 70-80 PSI on a properly charged system.
 

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Hissing sound at the evaporator may mean a thermal expansion valve is not working properly.

I would always diagnose AC problems with a set of manifold gauges. Otherwise it's like shooting in the dark.


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A small amount of refrigerant compared to a full charge will not have the same static charge; it will be lower.
In the closed system, there will be an equilibrium between the liquid R134a and the vapor R134a so this will not vary too much except for system temperature.

That's why static pressure is essentially only useful for determining if pressure is enough to actuate the pressure switch.
 

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Discussion Starter #8
Soooooo, after replacing the lines I went up to the shop to have it all vacuum tested and recharged. I asked the guy who evacuated it what the weight for the r134a was and he replied with a "1.14 lbs". I knew that the factory spec weight was 1.43 lbs. That's definitely enough to cut off the system. We hooked it all up, drew a vacuum, and charged it. It blew ice cold and I'm a very happy camper.

Thanks everyone for the suggestions and what not. It was just that simple.


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Glad you didn't have to rip the dash apart to get to the evaporator or thermal expansion valve.


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In the closed system, there will be an equilibrium between the liquid R134a and the vapor R134a so this will not vary too much except for system temperature.

That's why static pressure is essentially only useful for determining if pressure is enough to actuate the pressure switch.
Yes, but if have an A/C system blowing warm and I hook up a set of gauges and see, for example, static pressures of 40 PSI, I can pretty much guarantee that the system is low on refrigerant. That would still be enough to actuate the pressure switch, but not enough for the air conditioning to work efficiently. Or, if I were to see static pressures of 150 PSI, I can pretty much tell that someone overcharged the system.
 
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