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I'm not an a/c expert, but I believe it gets that signal from the trinary switch; when the low side pressure hits a certain point it cuts the compressor, when pressure drops it kicks it back on (confusingly, this switch will also cut the compressor if it reads too little system pressure?). Also from a temp sensor in the evaporative core inside the dash, to keep it from icing up.

Edited by SmashedGlass

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I'm not an a/c expert, but I believe it gets that signal from the trinary switch; when the low side pressure hits a certain point it cuts the compressor, when pressure drops it kicks it back on (confusingly, this switch will also cut the compressor if it reads too little system pressure?). Also from a temp sensor in the evaporative core inside the dash, to keep it from icing up.

 

That makes sense. The second time I charged my system, it didn't immediately come on until after a good bit of refrigerante had been loaded.

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AFAIK, both pressure and temp sensors. Trinary switch for pressure (cuts when low side pressure reaches certain point, kicks back on when drops below another) and a temp sensor in the evap core to prevent it from icing up.

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Okay I've got New o rings in place. The a/c worked beautifully for about ten minutes. Now I've got warm coming out of the vents. The compressor doll it's running. I checked the pressure Witt a gauge and got nothing. Checked the high pressure line and its got plenty of pressure. If I let it sit for awhile slowly the pressure comes up on the low pressure side. Any clues? Forgive any typographical errors I am Swype ing on my phone.

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From what I've read up on (once again, I'm in no way an a/c expert) what you describe could be a bad expansion valve, attached to the evap core. Could also be evap core icing up.

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All are helpful and informative suggestions. Didn't know about the temp sensor behind the dash.

Okay so, the a/c works again. All on it's own. My only issue now is that it cycles on and off pretty frequently. Sometimes when it cycles off it will remain off and the only way I can get cold air again is if I disengage the air conditioning, and then re-engage it (either by turning the thermostat off and then back to a/c, or switching from a/c to heat, and then back to a/c)

Could I ask by any chance if you know how much pressure your system has when it is running at idle? in PSI?

Thanks for all the replies SmashedGlass. Your thread about your own a/c has turned into a very helpful thread for others as well.

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My a/c is currently non-functional due to....low coolant charge :D

 

None of my books mention the pressures it should be at--they always say "...a qualified a/c mechanic....". You could call one of those kinda

guys and ask, they may tell you. Anyone have the factory service manuals handy? They might have a figure.

Edited by SmashedGlass

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All are helpful and informative suggestions. Didn't know about the temp sensor behind the dash.

 

Okay so, the a/c works again. All on it's own. My only issue now is that it cycles on and off pretty frequently. Sometimes when it cycles off it will remain off and the only way I can get cold air again is if I disengage the air conditioning, and then re-engage it (either by turning the thermostat off and then back to a/c, or switching from a/c to heat, and then back to a/c)

 

Could I ask by any chance if you know how much pressure your system has when it is running at idle? in PSI?

 

Thanks for all the replies SmashedGlass. Your thread about your own a/c has turned into a very helpful thread for others as well.

 

I think you are supposed to take the readings when the compressor is running. Are you measuring pressure with a manifold guage set or the little can top things that come with the refrigerant?

Edited by MR_Loyale

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From what I've read up on (once again, I'm in no way an a/c expert) what you describe could be a bad expansion valve, attached to the evap core. Could also be evap core icing up.

 

LOL. None of use are a/c experts, we just play them on the internet. I can say for a fact I think you know more about a/c (at least Loyale a/c, which is the only one I care about right now) than the "expert" that "fixed" mine in 2006 - only for it to leak out a week later.

Edited by MR_Loyale

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I'm using the crappy little gauge that comes with the refrigerant cans. I'm wondering if somebody with worKing a/c can check the pressure of their low side line(refilling line) at idle with compressor running and report back how many PSI it measures at. Mine is reading 45psi right now. Waiting for the compressor to turn itself off to report pressure reading at that time.

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Check out this guys videos, they're very informative on how automotive HVAC systems work, and how to work on them. Bonus, he's using a Subaru Legacy for demonstrating most of the repairs:

 

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I'm using the crappy little gauge that comes with the refrigerant cans. I'm wondering if somebody with worKing a/c can check the pressure of their low side line(refilling line) at idle with compressor running and report back how many PSI it measures at. Mine is reading 45psi right now. Waiting for the compressor to turn itself off to report pressure reading at that time.

 Is that the interdynamics (IDQ) refrigerant?  My R12 to R134a kit was from them and it included a dvd. It stated the pressure must be measured with the compressor running. The value it reads is dependent upon the ambient temperature.

 

Here is a video that might help. It has temp/pressure charts:

 

 

http://video.oreillyauto.com/v/23351/how-to-re-charge-ac-system-interdynamics-af1-r134a/

 

 

Temp-pressure-chart-33776F.jpg

Edited by MR_Loyale

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I've found out that the OEM amounts of r12 for our cars varied from 28 to 30 ounces of refrigerant.

 

All my pressure readings were with the a/c on max with the engine running.

My pressure readings are varying, and that's what I'm asking about

When the system is first turned on, I get high pressure readings on the low side. 45-55 PSI.

After about ten minutes that pressure reading is down to 25-30 psi and it's always around those pressures that my compressor turns off.


Forgot all about the sight glass on the drier. Wiped that off and checked it out. Lots of bubbles. My high side lines are also getting pretty hot. I've read conflicting reports that high side lines being hot is a result of there being too much pressure in the system or too little pressure in the system.

I've read also that bubbles in the sight glass definitely means to little pressure, so I'll be buying and adding another can to it soon and will report back.
 

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I've found out that the OEM amounts of r12 for our cars varied from 28 to 30 ounces of refrigerant.

 

All my pressure readings were with the a/c on max with the engine running.

 

My pressure readings are varying, and that's what I'm asking about

 

When the system is first turned on, I get high pressure readings on the low side. 45-55 PSI.

 

After about ten minutes that pressure reading is down to 25-30 psi and it's always around those pressures that my compressor turns off.

 

 

Forgot all about the sight glass on the drier. Wiped that off and checked it out. Lots of bubbles. My high side lines are also getting pretty hot. I've read conflicting reports that high side lines being hot is a result of there being too much pressure in the system or too little pressure in the system.

 

I've read also that bubbles in the sight glass definitely means to little pressure, so I'll be buying and adding another can to it soon and will report back.

 

 

When your system reads 25-30 psi what is the ambient temp? Higher than 65F? If so then you need more refrigerant.

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higher, yes. pushing 90 degrees. I'm going to add more tomorrow and see how that works out. I'm also thinking it's low due to air bubbles in the sight glass and how the system performs better at lower ambient temperature.

 

this thread is awesome and very insightful. thanks for all the help.

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I've read also that bubbles in the sight glass definitely means to little pressure, so I'll be buying and adding another can to it soon and will report back.

 

Bubbles mean too little refridgerant, not too little pressure.  It's important to remember that these are 2 entirely different things.

 

I believe what is happening is you did not evacuate the system first after replacing o-rings, so you are trying to push refrigerant into a system that already has air and moisture in it.  You're compressor is pumping and making pressure, but you aren't getting the condesation/evaporation action to the degree needed because your system has nitrogen,CO2, and watervapor in it.

 

The refill cans you buy at parts stores should only be used on a closed system that has never been depressurized, or you need to take it to a place that can vac out all the air before trying to fill it.

 

 

 

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Bubbles mean too little refridgerant, not too little pressure.  It's important to remember that these are 2 entirely different things.

 

I believe what is happening is you did not evacuate the system first after replacing o-rings, so you are trying to push refrigerant into a system that already has air and moisture in it.  You're compressor is pumping and making pressure, but you aren't getting the condesation/evaporation action to the degree needed because your system has nitrogen,CO2, and watervapor in it.

 

The refill cans you buy at parts stores should only be used on a closed system that has never been depressurized, or you need to take it to a place that can vac out all the air before trying to fill it.

 

 

 

 

Yes yes. VERY important. If trying to push refrigerant into a system that has air as well, the results will not be good. I think  you nailed it Gloyale.

 

175eya - did you use a vacuum pump to evacuate the system before you put in the refrigerant? If not, you will never get your system working for the reasons Gloyale has stated above. Plus you will ruin your system with the moisture. Get the system evacuated or get a vacuum pump and manifold gauge set and do it yourself. Harbor Freight has both and you can get them for under $160 in total. If you have a buddy who also has ac trouble, maybe you can split the cost. Or take it somewhere and have them do it.  Also they can test to see if it will hold a vaccum. Then refill with refrigerant. 

 

I ran the vacuum for an hour to ensure all the moisture boiled off when I did mine.

Edited by MR_Loyale

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Willing to sacrifice our looooooooooooooooove

Great song.

And about previous comments... :unsure: ......

Didn't really do any of that. :wacko:

lol

I just threw a can of r134a with oil in it at it, then I changed the o-rings, and filled it again.

It works good...when it works.

maybe one day I'll do it right. If the Compressor survives. I went into this with the mentality that it didn't work to begin with anyway, I'll do whatever I can do to try and get it to work and if it does, cool. (No pun intended). If not, oh well.

We'll see though ;)

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