AC system over pressurized??
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From: Southwest
AC system over pressurized??
Well, I finally found some freon to recharge my system and look for the leak. It took close to 3 cans but when I seen the bubbles disappear, I stopped the freon flow and checked the guages. My low side showed 55 and high side 275. How could that be when I stopped the flow when the bubbles disappeared? Now I think I either over pressurized the system, or the guages are reading incorrectly. I tried to let some pressure out, but I only got down to 50/250 and now I see bubbles in the sight glass 
Is there a way to service freon fully without inducing an over pressure condition?
Is there a way to service freon fully without inducing an over pressure condition?
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Those pressures sound OK, depending on ambient. Did you get cold air? Bubbles are probably the least accurate indicator.
A/C issues are more art than science, well sort of. That is why my local garage evacuates and recharges ($250.00) for a dash board switch (not pcar). then adds on parts and labor. The point being, even with gauges, you don't really know what is in there. If you start empty, you can be pretty sure how many ozs you put in if you can count the cans or have a recharge station. Gauges are the best indicator if you are not going to open it up and everything is working.
Another factor to complicate the equation, if there have been any leaks, you don't know how much oil is left. Another reason they want to start empty and charge from there.
A/C issues are more art than science, well sort of. That is why my local garage evacuates and recharges ($250.00) for a dash board switch (not pcar). then adds on parts and labor. The point being, even with gauges, you don't really know what is in there. If you start empty, you can be pretty sure how many ozs you put in if you can count the cans or have a recharge station. Gauges are the best indicator if you are not going to open it up and everything is working.
Another factor to complicate the equation, if there have been any leaks, you don't know how much oil is left. Another reason they want to start empty and charge from there.
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3 x 14oz cans would be about right for an empty system with rear air.
The pressures should be measured at 1500 RPM with a large box fan blowing at the front of the car. Here is a chart for ambient air temp versus pressure. Of course, LV is often off the chart. Both of your readings are high for just about any temp, but that can happen if you have been running the system for a long time charging it and it is overheated. Generally 20-30 lowside and 175-250 high, again, depending on ambient temp, unless overheated.
The pressures should be measured at 1500 RPM with a large box fan blowing at the front of the car. Here is a chart for ambient air temp versus pressure. Of course, LV is often off the chart. Both of your readings are high for just about any temp, but that can happen if you have been running the system for a long time charging it and it is overheated. Generally 20-30 lowside and 175-250 high, again, depending on ambient temp, unless overheated.
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From: Buckeye, AZ
Originally Posted by Darien Nunn
I tried to let some pressure out, but I only got down to 50/250 and now I see bubbles in the sight glass
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From: Southwest
Aw man, I was more afraid of blowing something with the high pressures 
I was using that chart, but during the entire time 1-3 cans, the pressures were way high. It seems like there are different pressures during the actual freon charging and the final readings.
I thought the sight glass was the way to go because some folks don't have the guages and that's all they have to go by.
I was using that chart, but during the entire time 1-3 cans, the pressures were way high. It seems like there are different pressures during the actual freon charging and the final readings.
I thought the sight glass was the way to go because some folks don't have the guages and that's all they have to go by.
Originally Posted by Bill Ball
Now you have no good idea how much you actually have in the system. Charging to a known weight on a fully discharged/evacuated system is the way to go. You had done that until you did the last step.
Last edited by Darien; Aug 3, 2007 at 02:42 PM.
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From: Oxford, CT
Your pressures definitely sound too high.
You don't know what those bubbles are, so you can't go by their appearance/disappearance as an indicator or proper charge. If you did not evacuate the air in the fill line on your gage manifold, or you used a can of recharge with the little 6" hose on it, then you probably blew a bunch of air into the system with the freon, making those bubbles you saw air bubbles under too-high pressure as opposed to gaseous freon bubbles under too-low pressure. Or maybe the air was already in the system previously?
You will be best off at this point with a complete evacuation (24 hours under vacuum is sometimes recommended. especially to remove any residual moisture) and recharge with dye, just in case you are leaking.
Good luck!
You don't know what those bubbles are, so you can't go by their appearance/disappearance as an indicator or proper charge. If you did not evacuate the air in the fill line on your gage manifold, or you used a can of recharge with the little 6" hose on it, then you probably blew a bunch of air into the system with the freon, making those bubbles you saw air bubbles under too-high pressure as opposed to gaseous freon bubbles under too-low pressure. Or maybe the air was already in the system previously?
You will be best off at this point with a complete evacuation (24 hours under vacuum is sometimes recommended. especially to remove any residual moisture) and recharge with dye, just in case you are leaking.
Good luck!
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Chronic Tool Dropper
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Darien--
Engine at 1500 RPM or so, fan on high for charging, 2 for checking pressures and temperatures. Were both fans running OK while you were charging and testing? Very Important! Ambient also plays a big part in what you see.
The temp at the center vent will likely not go below pass floor temp minus about 40 degrees. Toss the thermometer down there and get a reading, then get the center vent temp to see how close you are.
Did you evacuate well and prevent air from contaminating during charging? This means purging the hoses with freon before pushing a hose-full of air into the system with the new gas.
If you were working at a typical LV temp of 85-100f, And the compressor isn't new and you didn't clean the evaporator, the pressures you share are not really out of line. You'll see a better center vent temp after driving the car a little, getting the car cooled down some, improved airflow through the condenser. The load should come down to the point where you are pushing the freeze switch a little. At that time, 35 PSI low side might be expected, with 35-40 degree vent temps. It can get lower with cleaning. excellent vacuum, lots of care in how you charge.
Now the $64 question-- Were you able to find the leaks OK, and are they gone now with the new charge? I could use the sniffer back to work on a soCal'ers car next weekend if you are done with it.
Engine at 1500 RPM or so, fan on high for charging, 2 for checking pressures and temperatures. Were both fans running OK while you were charging and testing? Very Important! Ambient also plays a big part in what you see.
The temp at the center vent will likely not go below pass floor temp minus about 40 degrees. Toss the thermometer down there and get a reading, then get the center vent temp to see how close you are.
Did you evacuate well and prevent air from contaminating during charging? This means purging the hoses with freon before pushing a hose-full of air into the system with the new gas.
If you were working at a typical LV temp of 85-100f, And the compressor isn't new and you didn't clean the evaporator, the pressures you share are not really out of line. You'll see a better center vent temp after driving the car a little, getting the car cooled down some, improved airflow through the condenser. The load should come down to the point where you are pushing the freeze switch a little. At that time, 35 PSI low side might be expected, with 35-40 degree vent temps. It can get lower with cleaning. excellent vacuum, lots of care in how you charge.
Now the $64 question-- Were you able to find the leaks OK, and are they gone now with the new charge? I could use the sniffer back to work on a soCal'ers car next weekend if you are done with it.
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From: Buckeye, AZ
Originally Posted by Darien Nunn
Aw man, I was more afraid of blowing something with the high pressures
I was using that chart, but during the entire time 1-3 cans, the pressures were way high. It seems like there are different pressures during the actual freon charging and the final readings.
I thought the sight glass was the way to go because some folks don't have the guages and that's all they have to go by.
I was using that chart, but during the entire time 1-3 cans, the pressures were way high. It seems like there are different pressures during the actual freon charging and the final readings.
I thought the sight glass was the way to go because some folks don't have the guages and that's all they have to go by.
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From: Southwest
Hi Bob,
I evacuated the system but not the servicing hoses. I missed the 1500 rpm step, guess it will take 2.
As for the leak, I just now got the freon to search for it, I'll try to get the sniffer back to you before next weekend
I evacuated the system but not the servicing hoses. I missed the 1500 rpm step, guess it will take 2
.As for the leak, I just now got the freon to search for it, I'll try to get the sniffer back to you before next weekend
Originally Posted by dr bob
Darien--
Engine at 1500 RPM or so, fan on high for charging, 2 for checking pressures and temperatures. Were both fans running OK while you were charging and testing? Very Important! Ambient also plays a big part in what you see.
The temp at the center vent will likely not go below pass floor temp minus about 40 degrees. Toss the thermometer down there and get a reading, then get the center vent temp to see how close you are.
Did you evacuate well and prevent air from contaminating during charging? This means purging the hoses with freon before pushing a hose-full of air into the system with the new gas.
If you were working at a typical LV temp of 85-100f, And the compressor isn't new and you didn't clean the evaporator, the pressures you share are not really out of line. You'll see a better center vent temp after driving the car a little, getting the car cooled down some, improved airflow through the condenser. The load should come down to the point where you are pushing the freeze switch a little. At that time, 35 PSI low side might be expected, with 35-40 degree vent temps. It can get lower with cleaning. excellent vacuum, lots of care in how you charge.
Now the $64 question-- Were you able to find the leaks OK, and are they gone now with the new charge? I could use the sniffer back to work on a soCal'ers car next weekend if you are done with it.
Engine at 1500 RPM or so, fan on high for charging, 2 for checking pressures and temperatures. Were both fans running OK while you were charging and testing? Very Important! Ambient also plays a big part in what you see.
The temp at the center vent will likely not go below pass floor temp minus about 40 degrees. Toss the thermometer down there and get a reading, then get the center vent temp to see how close you are.
Did you evacuate well and prevent air from contaminating during charging? This means purging the hoses with freon before pushing a hose-full of air into the system with the new gas.
If you were working at a typical LV temp of 85-100f, And the compressor isn't new and you didn't clean the evaporator, the pressures you share are not really out of line. You'll see a better center vent temp after driving the car a little, getting the car cooled down some, improved airflow through the condenser. The load should come down to the point where you are pushing the freeze switch a little. At that time, 35 PSI low side might be expected, with 35-40 degree vent temps. It can get lower with cleaning. excellent vacuum, lots of care in how you charge.
Now the $64 question-- Were you able to find the leaks OK, and are they gone now with the new charge? I could use the sniffer back to work on a soCal'ers car next weekend if you are done with it.
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From: Southwest
Hi Bill,
I tried calling you on your cell. Again, I'll have to get another person for the 1500 run...Thanks 
I tried calling you on your cell
. Again, I'll have to get another person for the 1500 run...Thanks
Originally Posted by Bill Ball
I go by the chart I posted, although it appears to be pretty conservative, perhaps due to having higher than ambient temps due to overheating as I mentioned. Recheck the pressures with the engine rev'd to 1500 or so. I'll bet the lowside in no longer that high. It should be less than 30 unless you have run it stationary for a long time.
Chronic Tool Dropper
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Darien--
I creatively jam a long skinny screwdriver through the throttle mechanism to hold it open a little. Your linkage is probably a little different but you should be able to get it somehow. Congrats on getting it all together!
I creatively jam a long skinny screwdriver through the throttle mechanism to hold it open a little. Your linkage is probably a little different but you should be able to get it somehow. Congrats on getting it all together!
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From: Manchester,NH
It's common for a defective expansion valve to stick closed, however, the expansion valve can also stick open. This is indicated by higher than normal low side pressure, and slightly higher than normal high side pressure. This might appear as a weak compressor or slightly overcharged system.
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From: Stockton, CA
Darien
Probably the safest route is too totally evacuate the system and refill it to spec.....that way you are 100% sure you have the right amount of R12...... Then start taking a look at pressures at 1500rpm.....
Probably the safest route is too totally evacuate the system and refill it to spec.....that way you are 100% sure you have the right amount of R12...... Then start taking a look at pressures at 1500rpm.....
