AC Evacuation and Charging issues
04-05-2019, 06:09 PM
#1
Three Wheelin'
Thread Starter
AC Evacuation and Charging issues
just finished replacing rear evap/expansion valve, drier, along with most of the O-rings. car was previously converted to R134 and worked fine prior to my decision to replace a capped off rear evap. might have made a mistake in having a good intentioned neighbor help with the recharge; he is a retired home AC repair man who has some impressive tools including a digital scale and digital gauges. he told me over and over he knows what he is doing, but when he kept forgetting the original weight of the 134 tank, I should have known I might have made mistake.
factory fill for R12 is 2.42 pounds. I wanted to start at 80% with R134 which is 1.93, so we added 2.0 pounds. he felt the sight glass was not clear, so he kept added Freon until he was happy with the visual, and lost count of correct weight. not sure if I have 2.2 or 2.6 in the system??? low side is about 38 and high about 200 with 80' ambient temp. cooling is good, but not great with front dash temp at about 52, and rear evap temp at 40. how much does a system need to be overcharged to adversely effect cooling?
in addition, I seem to have voltage issues? with AC off, I have 13.8 volts. with AC on and fan on low or med, I get 13.5, and with fan on high: 13.4. turn on headlights and I get 13.0, and high beams take it down to 12.6. if the AC is overcharged can it create a greater voltage draw? do I have an alternator issue? battery is recent
FYI, FWIW: I have done the prescribed HVAC control unit external relay replacement, and 4 amp in line fuse for freeze switch; any other relays to examine on CE?
factory fill for R12 is 2.42 pounds. I wanted to start at 80% with R134 which is 1.93, so we added 2.0 pounds. he felt the sight glass was not clear, so he kept added Freon until he was happy with the visual, and lost count of correct weight. not sure if I have 2.2 or 2.6 in the system??? low side is about 38 and high about 200 with 80' ambient temp. cooling is good, but not great with front dash temp at about 52, and rear evap temp at 40. how much does a system need to be overcharged to adversely effect cooling?
in addition, I seem to have voltage issues? with AC off, I have 13.8 volts. with AC on and fan on low or med, I get 13.5, and with fan on high: 13.4. turn on headlights and I get 13.0, and high beams take it down to 12.6. if the AC is overcharged can it create a greater voltage draw? do I have an alternator issue? battery is recent
FYI, FWIW: I have done the prescribed HVAC control unit external relay replacement, and 4 amp in line fuse for freeze switch; any other relays to examine on CE?
Last edited by merchauser; 04-07-2019 at 09:14 AM.
04-05-2019, 06:36 PM
#2
Rennlist Member
The correct fill for R134 is about 90% that of R12 on a weight basis. The amount needed depends on whether one has the rear a/c option or not. If the discharge pressure is 200 psig I doubt that would be a problem at your ambient temperature but then you did not specify at what rpm's that pressure reading was taken.
The amount of gas in the system has no impact on current draw and your voltage numbers look fine to me assuming they are at idle- remember the alternator has a limited capacity and at idle cannot be expected to supply full load. Your voltage should be back to about 13.5 volts once the motor runs at 2k or greater if my memory serves me correctly. Once the voltage is down to about 12.5 volts you are draining from the battery as well as whatever the alternator is putting out.
The amount of gas in the system has no impact on current draw and your voltage numbers look fine to me assuming they are at idle- remember the alternator has a limited capacity and at idle cannot be expected to supply full load. Your voltage should be back to about 13.5 volts once the motor runs at 2k or greater if my memory serves me correctly. Once the voltage is down to about 12.5 volts you are draining from the battery as well as whatever the alternator is putting out.
04-05-2019, 06:57 PM
#3
Three Wheelin'
Thread Starter
The correct fill for R134 is about 90% that of R12 on a weight basis. The amount needed depends on whether one has the rear a/c option or not. If the discharge pressure is 200 psig I doubt that would be a problem at your ambient temperature but then you did not specify at what rpm's that pressure reading was taken.
The amount of gas in the system has no impact on current draw and your voltage numbers look fine to me assuming they are at idle-
The amount of gas in the system has no impact on current draw and your voltage numbers look fine to me assuming they are at idle-
WSM R12 for my car with rear AC is 2.42 pounds. following a near Abbott and Costello filling routine, I could have anywhere from 2.2 (about 90%) to 2.6 pounds (10% overcharged) in system. if I am overcharged by 10%, will that adversely effect cooling? I don't feel it is cooling at its best and may have been better before.
pressure readings were taken at idle. early this AM, I had a 100 high side static read. (low side was not connected)
04-06-2019, 05:05 AM
#4
Rennlist Member
voltage readings were at idle; glad to hear they seem alright...?? will recheck with RPM increase. guess I can take this, as an issue, off the table. also glad to hear overcharge would have nothing to do with voltage.
WSM R12 for my car with rear AC is 2.42 pounds. following a near Abbott and Costello filling routine, I could have anywhere from 2.2 (about 90%) to 2.6 pounds (10% overcharged) in system. if I am overcharged by 10%, will that adversely effect cooling? I don't feel it is cooling at its best and may have been better before.
pressure readings were taken at idle. early this AM, I had a 100 high side static read. (low side was not connected)
WSM R12 for my car with rear AC is 2.42 pounds. following a near Abbott and Costello filling routine, I could have anywhere from 2.2 (about 90%) to 2.6 pounds (10% overcharged) in system. if I am overcharged by 10%, will that adversely effect cooling? I don't feel it is cooling at its best and may have been better before.
pressure readings were taken at idle. early this AM, I had a 100 high side static read. (low side was not connected)
Paul,
When are you colonial boys going to ditch using those stupid British units General Cornwallis dumped on you after he surrendered? The 928 was built in Germany- they are thoroughly metric!
According to my logic you should be following the charge numbers listed for the 93 GTS that was equipped with R134a in the factory- that requires 1040gms [37 ounces] with rear a/c- the only caveat is that I am not totally sure if the GTS system has the same native volume given there are some small differences in the filter drier but I doubt they would be significant- either way that is what I refer for my R12 equipped GTS now running R134a because your environmental lot banned R12 [no complaints by the way!]. Thus it seems Porsche used a factor of 0.95 for R134a compared to R12- if you study the issue you will find conversion factors quoted in the range 0.9 to 0.95.
A system that is overcharged will have reduced performance and worse, there is the possibility of liquid hitting the compressor and buggering it up. As a marker I reckon the system loses about 12 ounces by the time the low pressure switch drops out and then it has about 24 ounces left in it. Just before it reaches the stage where the pressure switch locks out the compressor I can always tell it is going to happen as the a/c performance drops noticeably but until that decay point it works fine.
The pressure at idle is more or less meaningless- the system needs to get fully warmed and then rev the motor to at least 2k rpm to get any meaningful data. The pressure should fall within the range shown in the WSM for the R134 system which at your ambient temps will be in the region of 15 to 18 barg. There will be a little latitude in the filling amount but not much and if one is going to err it is way better to be on the low side. When testing for performance the trick is to hose some water onto the condenser to simulate the effect of the "missing" air flow without which the refrigerant will not condense as well..
04-06-2019, 07:44 AM
#5
Three Wheelin'
Thread Starter
interesting regarding GTS capacity specs. 37 oz. is roughly 95% of my 40.56 (following your lead with units. lol). I will recheck my readings, but I MAY have up to 42 oz in my system and no way to know for sure. would you think an additional 5 oz would adversely effect cooling performance? I could start from scratch, but would obviously prefer not to...…(why is temp reading at rear unit lower?)
04-06-2019, 08:55 AM
#6
Rennlist Member
interesting regarding GTS capacity specs. 37 oz. is roughly 95% of my 40.56 (following your lead with units. lol). I will recheck my readings, but I MAY have up to 42 oz in my system and no way to know for sure. would you think an additional 5 oz would adversely effect cooling performance? I could start from scratch, but would obviously prefer not to...…(why is temp reading at rear unit lower?)
04-06-2019, 01:07 PM
#7
Recover or remove the refrigerant.
Evacuate the system. If your buddy has a digital micron gauge, use it.
The resolution (accuracy) of measuring vacuum in "inHg" (inches of mercury) compared to microns or similar scale
is not good. If you have residual air in the system it will raise the pressures and lead you down many wrong roads.
If your original R12 factory charge was ,for example, 2.42 pounds or 38.72 ounces, start off with 80% of the that weight, or 31 ounces.
Don't forget to allow for the volume or weight that is retained in the service equipment and service hoses.
A wise practice is to weigh the 30 pound R134a canister by itself on a digital scale. Write the date and starting weight with a marker
on the canister. When you get done with the job weigh the can again and write the date and weight on the can.
The rear AC is useless; my opinion after owning 3 sharks. I never turned it on.
A good procedure is to use a 4 hose service set; having the low side and high side hoses to the vehicle with their snap on coupler
valves closed, the refrigerant line connected to the R134a canister with the valve closed at the canister closed.
Pull a vacuum on all the lines. Then, allow your refrigerant lines to fill with refrigerant up to the service port on the vehicle
system you intend to charge through, and then zero out your weight scale before you start charging.
Be aware of safe procedures for charging by liquid vs gas.
Best practice is to ensure the HVAC vents (vacuum and servos) are working properly.
Windows up, Max AC temp on the temp dial, recirc mode, pick a medium fan speed.
Engine at idle (if you want to check pressures at a higher speed you can do
that later).
Walk around the front of car with a digital thermometer and write down the average ambient (outside air temp) you observed.
Allow the system to run for at least 5 to 10 minutes.
Note your initial starting charge, ie. 31 ounces, the ambient temp, the low and high side pressures.
At 'idle" , at 80F ambient, a good bogey for this Shark is 200 psi on the high.
(A few more data points for you would be 70F 170 psi, 90F 238 psi).
Your low side pressure of 38 psi reflects an evap core temperature of about 43F.
Your front vent temp (front evap) was 52F. Depending upon how well the HVAC flaps
are doing and how long the air was recirculating (assuming your fresh air flap is sealed well),
this could be a decent or a not too good number. At this juncture, I would reflect on those items before
I started adding or removing refrigerant.
With R134a we prefer to ignore the site glass because the flow is not clear and tends to be milky.
Its normal to see voltage drops as you start to put a load on the system.
However, an overcharged system does take power away from the motor.
Rear AC is useless, my opinion after owning 3 sharks, I never turned it on.
Evacuate the system. If your buddy has a digital micron gauge, use it.
The resolution (accuracy) of measuring vacuum in "inHg" (inches of mercury) compared to microns or similar scale
is not good. If you have residual air in the system it will raise the pressures and lead you down many wrong roads.
If your original R12 factory charge was ,for example, 2.42 pounds or 38.72 ounces, start off with 80% of the that weight, or 31 ounces.
Don't forget to allow for the volume or weight that is retained in the service equipment and service hoses.
A wise practice is to weigh the 30 pound R134a canister by itself on a digital scale. Write the date and starting weight with a marker
on the canister. When you get done with the job weigh the can again and write the date and weight on the can.
The rear AC is useless; my opinion after owning 3 sharks. I never turned it on.
A good procedure is to use a 4 hose service set; having the low side and high side hoses to the vehicle with their snap on coupler
valves closed, the refrigerant line connected to the R134a canister with the valve closed at the canister closed.
Pull a vacuum on all the lines. Then, allow your refrigerant lines to fill with refrigerant up to the service port on the vehicle
system you intend to charge through, and then zero out your weight scale before you start charging.
Be aware of safe procedures for charging by liquid vs gas.
Best practice is to ensure the HVAC vents (vacuum and servos) are working properly.
Windows up, Max AC temp on the temp dial, recirc mode, pick a medium fan speed.
Engine at idle (if you want to check pressures at a higher speed you can do
that later).
Walk around the front of car with a digital thermometer and write down the average ambient (outside air temp) you observed.
Allow the system to run for at least 5 to 10 minutes.
Note your initial starting charge, ie. 31 ounces, the ambient temp, the low and high side pressures.
At 'idle" , at 80F ambient, a good bogey for this Shark is 200 psi on the high.
(A few more data points for you would be 70F 170 psi, 90F 238 psi).
Your low side pressure of 38 psi reflects an evap core temperature of about 43F.
Your front vent temp (front evap) was 52F. Depending upon how well the HVAC flaps
are doing and how long the air was recirculating (assuming your fresh air flap is sealed well),
this could be a decent or a not too good number. At this juncture, I would reflect on those items before
I started adding or removing refrigerant.
With R134a we prefer to ignore the site glass because the flow is not clear and tends to be milky.
Its normal to see voltage drops as you start to put a load on the system.
However, an overcharged system does take power away from the motor.
Rear AC is useless, my opinion after owning 3 sharks, I never turned it on.
Last edited by griffiths; 04-06-2019 at 01:09 PM. Reason: useless rear air
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04-06-2019, 02:55 PM
#8
Rennlist Member
Id say you gotta start over.
Who knows whats in there now.
When you say low is 38, is that PSI or degrees F?
How long did you pull a vac on the system, and what was the gauge reading with the vac at the very end of that.
Who knows whats in there now.
When you say low is 38, is that PSI or degrees F?
How long did you pull a vac on the system, and what was the gauge reading with the vac at the very end of that.
04-06-2019, 06:05 PM
#11
Three Wheelin'
Thread Starter
to continue, Griffiths and Fred: I looked over the GTS WSM. current ambient temp is 90'. my high side reading was 310 and my reading of the WSM suggests it should be slightly less than 250. clearly the system is overcharged. (?) in an attempt to save this charge, I evacuated some 134, and now reading @ 2k rpm is right at 250, and at idle 225. no time to play and report that car is cooling better. hoping that I am still in the green zone and will not need to start over, but not certain. what I do know, is my well intentioned friend was too focused on the sight glass.
FWIW: all in dash actuators, diaphragms, hoses, and manifold were addressed last year. compressor looks to be original. drier is new. I installed new expansion valve with new rear evap. when I dropped the lower AC lines, I lost about 1/4 oz. of oil. since the rear evap was totally braised/blocked off, I added 1 oz. to the evap. no idea how PO did 134 conversion, but I can tell you that the AC was blowing great prior to my work. I am only guessing from what I have read, that conversion was done with ester oil, as that will tolerate residual mineral oil from R12. so the oil I added was ester.
I did not replace the front expansion valve: could that be an issue? and
if the PO used PAG (HIGHLY doubtful) and I injected ester, would that attribute to this situation?
04-06-2019, 06:31 PM
#12
Rennlist Member
The rear a/c "robs Peter to pay Paul" in that the system performance drops dramatically when both are operating in hot/humid conditions. This is less of problem in manual transmission pre-GTS models as they have a bigger condenser acreage as those examples have no transmission cooler to squeeze in thus are that bit bigger. Models with the tranny cooler and the rear a/c work OK until about 30C ambient and struggle from those temperatures upwards. Switch the rear unit on and the front vents warm up noticeably.
I found the rear a/c useful when my daughters were little but like Griff I have not used the rear unit for years other than to test that it is still working. .To be effective in a very hot environment I reckon it would need anything up to about 40% extra surface area on the condenser and that assumes that the compressor could cope were such to be fitted. The stock system benefits passively by fitting good quality ceramic heat rejection film as I did but the thing is still a green house when all is said and done..
Thus the rear a/c system, although a useful addition, is clearly limited.
I found the rear a/c useful when my daughters were little but like Griff I have not used the rear unit for years other than to test that it is still working. .To be effective in a very hot environment I reckon it would need anything up to about 40% extra surface area on the condenser and that assumes that the compressor could cope were such to be fitted. The stock system benefits passively by fitting good quality ceramic heat rejection film as I did but the thing is still a green house when all is said and done..
Thus the rear a/c system, although a useful addition, is clearly limited.
04-06-2019, 06:38 PM
#13
Rennlist Member
The rear a/c "robs Peter to pay Paul" in that the system performance drops dramatically when both are operating in hot/humid conditions. This is less of problem in manual transmission pre-GTS models as they have a bigger condenser acreage as those examples have no transmission cooler to squeeze in thus are that bit bigger. Models with the tranny cooler and the rear a/c work OK until about 30C ambient and struggle from those temperatures upwards. Switch the rear unit on and the front vents warm up noticeably.
I found the rear a/c useful when my daughters were little but like Griff I have not used the rear unit for years other than to test that it is still working. .To be effective in a very hot environment I reckon it would need anything up to about 40% extra surface area on the condenser and that assumes that the compressor could cope were such to be fitted. The stock system benefits passively by fitting good quality ceramic heat rejection film as I did but the thing is still a green house when all is said and done..
Thus the rear a/c system, although a useful addition, is clearly limited.
I found the rear a/c useful when my daughters were little but like Griff I have not used the rear unit for years other than to test that it is still working. .To be effective in a very hot environment I reckon it would need anything up to about 40% extra surface area on the condenser and that assumes that the compressor could cope were such to be fitted. The stock system benefits passively by fitting good quality ceramic heat rejection film as I did but the thing is still a green house when all is said and done..
Thus the rear a/c system, although a useful addition, is clearly limited.
Agreed that running for full effect, just use one, but once settled, I like the air moving behind me too.
04-06-2019, 07:21 PM
#14
Rennlist Member
so many moving parts to address: let me start with you, jeff. unfortunately, I agree that I should probably start over, and am prepared to do that. low side was 38 psi. we pulled a vacuum for nearly 90 minutes down to 390 microns.
to continue, Griffiths and Fred: I looked over the GTS WSM. current ambient temp is 90'. my high side reading was 310 and my reading of the WSM suggests it should be slightly less than 250. clearly the system is overcharged. (?) in an attempt to save this charge, I evacuated some 134, and now reading @ 2k rpm is right at 250, and at idle 225. no time to play and report that car is cooling better. hoping that I am still in the green zone and will not need to start over, but not certain. what I do know, is my well intentioned friend was too focused on the sight glass.
FWIW: all in dash actuators, diaphragms, hoses, and manifold were addressed last year. compressor looks to be original. drier is new. I installed new expansion valve with new rear evap. when I dropped the lower AC lines, I lost about 1/4 oz. of oil. since the rear evap was totally braised/blocked off, I added 1 oz. to the evap. no idea how PO did 134 conversion, but I can tell you that the AC was blowing great prior to my work. I am only guessing from what I have read, that conversion was done with ester oil, as that will tolerate residual mineral oil from R12. so the oil I added was ester.
I did not replace the front expansion valve: could that be an issue? and
if the PO used PAG (HIGHLY doubtful) and I injected ester, would that attribute to this situation?
to continue, Griffiths and Fred: I looked over the GTS WSM. current ambient temp is 90'. my high side reading was 310 and my reading of the WSM suggests it should be slightly less than 250. clearly the system is overcharged. (?) in an attempt to save this charge, I evacuated some 134, and now reading @ 2k rpm is right at 250, and at idle 225. no time to play and report that car is cooling better. hoping that I am still in the green zone and will not need to start over, but not certain. what I do know, is my well intentioned friend was too focused on the sight glass.
FWIW: all in dash actuators, diaphragms, hoses, and manifold were addressed last year. compressor looks to be original. drier is new. I installed new expansion valve with new rear evap. when I dropped the lower AC lines, I lost about 1/4 oz. of oil. since the rear evap was totally braised/blocked off, I added 1 oz. to the evap. no idea how PO did 134 conversion, but I can tell you that the AC was blowing great prior to my work. I am only guessing from what I have read, that conversion was done with ester oil, as that will tolerate residual mineral oil from R12. so the oil I added was ester.
I did not replace the front expansion valve: could that be an issue? and
if the PO used PAG (HIGHLY doubtful) and I injected ester, would that attribute to this situation?
A discharge pressure of 250 psig sounds as though you are in the right drop zone. If the RH was 100% you would expect a pressure of 275 psig. If you know the actual RH you can try to interpolate between zero and 100% RH to arrive at a notional value- there will invariably be some error factor but not that much.
The oil used may have been PAG if the system was flushed out and all traces of mineral oil removed. POE was designed as a crossover lubricant suitable for both R12 and R134 but whether POE can used in a system that has been exposed to PAG I do not know. For sure I use POE for what little that is worth.. Doubtless Griff will know the answer to that one.
Whilst on the subject does anyone know the set point for the low pressure switch? For some weird reason Porsche does not include such info in the WSM or not that I have ever noticed such.
04-06-2019, 07:38 PM
#15
Rennlist Member
so many moving parts to address: let me start with you, jeff. unfortunately, I agree that I should probably start over, and am prepared to do that. low side was 38 psi. we pulled a vacuum for nearly 90 minutes down to 390 microns.
to continue, Griffiths and Fred: I looked over the GTS WSM. current ambient temp is 90'. my high side reading was 310 and my reading of the WSM suggests it should be slightly less than 250. clearly the system is overcharged. (?) in an attempt to save this charge, I evacuated some 134, and now reading @ 2k rpm is right at 250, and at idle 225. no time to play and report that car is cooling better. hoping that I am still in the green zone and will not need to start over, but not certain. what I do know, is my well intentioned friend was too focused on the sight glass.
FWIW: all in dash actuators, diaphragms, hoses, and manifold were addressed last year. compressor looks to be original. drier is new. I installed new expansion valve with new rear evap. when I dropped the lower AC lines, I lost about 1/4 oz. of oil. since the rear evap was totally braised/blocked off, I added 1 oz. to the evap. no idea how PO did 134 conversion, but I can tell you that the AC was blowing great prior to my work. I am only guessing from what I have read, that conversion was done with ester oil, as that will tolerate residual mineral oil from R12. so the oil I added was ester.
I did not replace the front expansion valve: could that be an issue? and
if the PO used PAG (HIGHLY doubtful) and I injected ester, would that attribute to this situation?
to continue, Griffiths and Fred: I looked over the GTS WSM. current ambient temp is 90'. my high side reading was 310 and my reading of the WSM suggests it should be slightly less than 250. clearly the system is overcharged. (?) in an attempt to save this charge, I evacuated some 134, and now reading @ 2k rpm is right at 250, and at idle 225. no time to play and report that car is cooling better. hoping that I am still in the green zone and will not need to start over, but not certain. what I do know, is my well intentioned friend was too focused on the sight glass.
FWIW: all in dash actuators, diaphragms, hoses, and manifold were addressed last year. compressor looks to be original. drier is new. I installed new expansion valve with new rear evap. when I dropped the lower AC lines, I lost about 1/4 oz. of oil. since the rear evap was totally braised/blocked off, I added 1 oz. to the evap. no idea how PO did 134 conversion, but I can tell you that the AC was blowing great prior to my work. I am only guessing from what I have read, that conversion was done with ester oil, as that will tolerate residual mineral oil from R12. so the oil I added was ester.
I did not replace the front expansion valve: could that be an issue? and
if the PO used PAG (HIGHLY doubtful) and I injected ester, would that attribute to this situation?
Notably, look at your low side temps, not pressure, although can you look up the temp from that.
You should have a reading on the low side generally below freezing.
https://www.ref-wiki.com/data-for-freon.html
Look to the WSM for more exact data on what you should see.
Charging by sight glass works for R12..not generally for R134. Which is why since R134 most cars dont have a sight glass...easy path to overcharging.