What the heck is going on with my A/C?
08-27-2010, 05:16 PM
#11
1st Gear Member
Join Date: Apr 2009
Location: AZ
Posts: 54
There is no vacuum in a properly operating, or dead flat, AC system; in fact it is quite the opposite Once charged the system is pressurized at 80 to 90psi when not operating, 25 to 50psi at the low side and 130 to 350psi at the high side--depending on the ambient temperature, with the higher pressures at higher outside temps.
The refrigerant leaves the can for the simple reason that the pressure in the can is higher than that of the low-side of the AC system.
The vacuum that is initially pulled on a system that has been opened up is to remove and air and moisture. By keeping the system subject to 29inHg or better vacuum for 30 to 40 minutes, the moisture is boiled off.
If the system has leaked down slowly, more slowly then the OPs has, and not been opened up then you don't need to) pull the vacuum to recharge it.
I had a 1986 Corolla years ago that I had "converted" to R134a that had to have a can loaded every two weeks because of its age, and that because R134a operates at higher pressures and had smaller molecules. Drove it for almost two years like that.
------------------------------------
OP, get a gauge set and see what the pressures look like. Here's a good temperature/pressure chart; and a "how-to" read the gauges cheat sheet:
.jpg)
There's a ton of good AC info on the web, also Haynes has a an auto AC system book that is at most FLAPS...
One last thought, you were holding the can upside down when you tried to add it--right?
The refrigerant leaves the can for the simple reason that the pressure in the can is higher than that of the low-side of the AC system.
The vacuum that is initially pulled on a system that has been opened up is to remove and air and moisture. By keeping the system subject to 29inHg or better vacuum for 30 to 40 minutes, the moisture is boiled off.
If the system has leaked down slowly, more slowly then the OPs has, and not been opened up then you don't need to) pull the vacuum to recharge it.
I had a 1986 Corolla years ago that I had "converted" to R134a that had to have a can loaded every two weeks because of its age, and that because R134a operates at higher pressures and had smaller molecules. Drove it for almost two years like that.
------------------------------------
OP, get a gauge set and see what the pressures look like. Here's a good temperature/pressure chart; and a "how-to" read the gauges cheat sheet:
There's a ton of good AC info on the web, also Haynes has a an auto AC system book that is at most FLAPS...
One last thought, you were holding the can upside down when you tried to add it--right?
08-27-2010, 06:36 PM
#13
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
After that it will suck in the first 2/3rds or so of the charge like a Hoover. But once that is in there it will be up to 20psi or so low side and want the remainder of the charge.
The FLAPS "re-charge" kits that come with a single short hose and a colour coded gauge are a waste of money--especially when you get get a nice manifold and gauge set for $30...
08-29-2010, 03:38 PM
#14
1st Gear Member
Join Date: Apr 2009
Location: AZ
Posts: 54
They told it to me pretty much exactly like I wrote it. That the system wouldn't pull a charge without a vacuum in the line, and you needed shop equipment to do it.
So I guess my question is, if the static pressure on the low (fill) side of the system is effectively equal to the atmospheric pressure at the elevation where you live, and the can is pressurized, then why can't I charge the system after I've replaced all the equipment? I understand the benefit of purging, but it doesn't explain why refrigerant wouldn't go into a closed system with the compressor cycling.
So I guess my question is, if the static pressure on the low (fill) side of the system is effectively equal to the atmospheric pressure at the elevation where you live, and the can is pressurized, then why can't I charge the system after I've replaced all the equipment? I understand the benefit of purging, but it doesn't explain why refrigerant wouldn't go into a closed system with the compressor cycling.
08-29-2010, 06:29 PM
#15
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
They told it to me pretty much exactly like I wrote it. That the system wouldn't pull a charge without a vacuum in the line, and you needed shop equipment to do it.
So I guess my question is, if the static pressure on the low (fill) side of the system is effectively equal to the atmospheric pressure at the elevation where you live, and the can is pressurized, then why can't I charge the system after I've replaced all the equipment? I understand the benefit of purging, but it doesn't explain why refrigerant wouldn't go into a closed system with the compressor cycling.
So I guess my question is, if the static pressure on the low (fill) side of the system is effectively equal to the atmospheric pressure at the elevation where you live, and the can is pressurized, then why can't I charge the system after I've replaced all the equipment? I understand the benefit of purging, but it doesn't explain why refrigerant wouldn't go into a closed system with the compressor cycling.
One thing that just occurred to me and not intending to insult anyone, you have done this before and understand that you have to screw the valve on the can fitting in all the way to first perforate the can's seal, and then open it to allow the oil or refrigerant to flow--right?
Also, if using a real gauge set you also have to make sure the plunger valve in the low side fitting has been opened by turning it clockwise to push the plunger valve downward.
Most of the little fill hoses from the FLAPS have a molded in pin that opens the plunger in the car's fitting...
08-29-2010, 06:41 PM
#16
5th Gear Member
Join Date: Feb 2010
Location: Connecticut
Posts: 2,549
If you open a system as stated already by cliffyk ,it has to have a vacuum pulled on it. Apparently you do not understand . There is no exception to this. This is basic refrigeration repair 101. This removes air and moisture from the system. You need to understand the basic principals of refrigeration if you are going to repair it yourself. Moisture which will be in any system that air has been allowed to infiltrate is bad news. Short version moisture can damage a system by creating acid. And air present will not allow it to run at the proper pressures etc.. , not to mention the moisture in the air issue. The shop guy did not lie to you. Yes you do need special equipment/ shop equipment as in a vacuum pump and a set of gauges. You need to know how to read these gauges. If you want to know more about the why's then google refrigeration repair. And if the system would not take a charge then your suction side/low side could have a higher pressure then whats in your can as in a restriction. Also just because the compressor fan clutch engages does not mean the compressor is pumping. If you do not know what you are doing adding to much refrigerant can damage the system. It will not cool properly by flooding the evaporator with liquid. And liquid back to the compressor is bad as it will destroy it. When it comes refrigerant more is not better. More=damage= huge repair bill .
08-29-2010, 06:45 PM
#17
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
If you open a system as stated already by cliffyk ,it has to have a vacuum pulled on it. Apparently you do not understand . There is no exception to this. This is basic refrigeration repair 101. This removes air and moisture from the system. You need to understand the basic principals of refrigeration if you are going to repair it yourself. Moisture which will be in any system that air has been allowed to infiltrate is bad news. Short version moisture can damage a system by creating acid. And air present will not allow it to run at the proper pressures etc.. , not to mention the moisture in the air issue. The shop guy did not lie to you. Yes you do need special equipment/ shop equipment as in a vacuum pump and a set of gauges. You need to know how to read these gauges. If you want to know more about the why's then google refrigeration repair. And if the system would not take a charge then your suction side/low side could have a higher pressure then whats in your can as in a restriction. Also just because the compressor fan clutch engages does not mean the compressor is pumping. If you do not know what you are doing adding to much refrigerant can damage the system. It will not cool properly by flooding the evaporator with liquid. And liquid back to the compressor is bad as it will destroy it. When it comes refrigerant more is not better. More=damage= huge repair bill .
08-29-2010, 07:08 PM
#18
1st Gear Member
Join Date: Apr 2009
Location: AZ
Posts: 54
OK.. not going to get into a pissing match
But that's exactly what I said, and I was told I was wrong. Look at my original post and the reply to that before you tell me what a dumbass I am. The response I got was a vacuum didn't have **** to do with whether or not the system would recharge.
And yes, I've recharged every single vehicle I've ever owned, that ever needed a charge, with gauges, and I've never had a problem, until I replaced a compressor, and I was told a vacuum was needed before it would accept any kind of charge.
Exactly what my original post said, until I was told I was WRONG.
And yes, I've recharged every single vehicle I've ever owned, that ever needed a charge, with gauges, and I've never had a problem, until I replaced a compressor, and I was told a vacuum was needed before it would accept any kind of charge.
Exactly what my original post said, until I was told I was WRONG.
08-29-2010, 07:46 PM
#19
5th Gear Member
Join Date: Feb 2010
Location: Connecticut
Posts: 2,549
Sorry my intention was not to make you look like a dumbass. I did go back and read, and I thought I was still responding to the person who started this post. You posted he lost the vacuum. You were wrong ,you only pull a vacuum once to remove moisture and air. Once you add refrigerant that vacuum is lost.The low side runs at a lower pressure not a vacuum. That is why you can add refrigerant. Properly operating system the low side pressure is lower then what is in the can. Depending on the ambient temp and other variables if you were to put on a set of gauges you should always read pressure not vacuum on both liquid and suction lines.
Last edited by DRAGUL; 08-29-2010 at 08:25 PM.
08-29-2010, 09:18 PM
#20
1st Gear Member
Join Date: Apr 2009
Location: AZ
Posts: 54
Sorry my intention was not to make you look like a dumbass. I did go back and read, and I thought I was still responding to the person who started this post. You posted he lost the vacuum. You were wrong ,you only pull a vacuum once to remove moisture and air. Once you add refrigerant that vacuum is lost.The low side runs at a lower pressure not a vacuum. That is why you can add refrigerant. Properly operating system the low side pressure is lower then what is in the can. Depending on the ambient temp and other variables if you were to put on a set of gauges you should always read pressure not vacuum on both liquid and suction lines.
I'm not arguing the dynamics of evap A/C systems, I'm wondering to the crowd at large, why the valve on the low side won't open to let the refrigerant into the system, and potentially straight out the leak.
My thinking is that just like the old barnyard water pump I grew up around, without a viscous prime, the compressor (pump) cannot draw refrigerant into the system. My rationale was, that the initial vacuum allows the refrigerant to be drawn into the system, and "primes" the compressor so that a continuous pumping action can occur. I understand that the static pressure of the system is lower than the static pressure of the charging can, but if the system can't "draw" based on the pumping action of the compressor, the valve will not open. That's pure speculation based on my knowledge of closed loop systems.
I swear to God, I'm not trying to be a dick, I'm just trying to make sure I understand.
Sorry OP. Looks like I've hijacked the post for educational purposes.
Thanks for any info.
Geren