Expansion Valve Replacement
07-09-2016, 11:59 AM
#1
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Thread Starter
Expansion Valve Replacement
'93, has 134a. Low pressure is too high, and high pressure is too low; indicates partially clogged expansion valve. I get cool air, but not enough. I have an R12 Robinair charging station which is a pump, gauges and reservoir with a heater for charging - left over from R12 usage. My question is if I replace the hoses (not the gauges) and replace with new or R134 hoses and flush the oil out of the pump, and piping and replace with proper oil in pump for 134, can I use this with 134?? or is it just too risky; By the time I go to this trouble, I should let a pro replace my valve, dryer and not try this myself.
07-09-2016, 12:05 PM
#2
i replaced all the parts my self. and let the pros charge the system. i think the gauges are calibrated different between 12 and 134. so you would be getting false readings.
07-09-2016, 12:50 PM
#3
Chronic Tool Dropper
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Steve--
A partially-clogged expansion valve will display too-low low pressure and too-high high pressure readings.
The inverse symptoms, to me, says a compressor pump isn't pumping. Maybe not the news you want to hear, but that's what they say. Or the expansion valve is stuck open.
You can swap hoses, purge the recovery canister completely, change the vacuum pump oil, and use the existing R12 gauges. Be aware that the pressure indications will be correct, no worries. But the related temperature readings on the gauges will be wrong for the R134a. If you have the tables and maybe even the molinear diagrams you'll be golden.
A partially-clogged expansion valve will display too-low low pressure and too-high high pressure readings.
The inverse symptoms, to me, says a compressor pump isn't pumping. Maybe not the news you want to hear, but that's what they say. Or the expansion valve is stuck open.
You can swap hoses, purge the recovery canister completely, change the vacuum pump oil, and use the existing R12 gauges. Be aware that the pressure indications will be correct, no worries. But the related temperature readings on the gauges will be wrong for the R134a. If you have the tables and maybe even the molinear diagrams you'll be golden.
07-09-2016, 01:49 PM
#4
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+1 on the not the expansion valve being clogged.
If the Expansion valve is stuck open it could lead to the symptoms, but if the compressor was run for any time with the valve stuck open it would likely result in compressor failing.
What are your high and low pressures?
If the Expansion valve is stuck open it could lead to the symptoms, but if the compressor was run for any time with the valve stuck open it would likely result in compressor failing.
What are your high and low pressures?
07-09-2016, 10:46 PM
#5
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I should state that the diagnosis above came from the packaging to the 134 gauge set which has red, blue and yellow lines. With the system running, the high line read under 50, the low was zero; and with a full can hooked to the yellow feed line it went to 190 whereupon I shut the valves to isolate the system and bleed off the pressure in the yellow line. I turned the valve and A/C on again w/o the yellow line open; The pressures were 140 and near zero in the high side. It seems nothing went into the system. There was cool air, but not cold, my infra red gun says 50 degrees; OAT was 80. I changed out the freeze switch a couple years ago. When running there is a steady flow of not really bubbles, but "smears" of fluid, (oily?) flowing across the sight glass on the dryer.
Dr. Bob: I'm confused by the statement about temperature readings. It sounds like the compressor isn't doing anything, but then how am I getting any cooling? It's been this way for some time. Maybe it has never been giving much pressure.
Dr. Bob: I'm confused by the statement about temperature readings. It sounds like the compressor isn't doing anything, but then how am I getting any cooling? It's been this way for some time. Maybe it has never been giving much pressure.
07-10-2016, 12:21 PM
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Steve,
I'm still confused by what you're saying.
1) What went to 190? Where you still feeding refrigerant when it went to 190?
2) Are you saying the pressures where 140 on the low and near 0 on the high? Or that the pressures on the high where cycling between 0 and 140? Either way my first thought is that the lines may be connected improperly. Where are you connecting your lines?
3) The sight glass on the dryer, ideally has few if any bubbles, primary use is to ensure a solid liquid column. As the oil is fully mixed in liquid refrigerant, you should not see oil moving across. If you are seeing oil it is more likely that there is no liquid at the sight glass.
First of all, I'm not recommending that anyone without training service their own AC systems. Refrigeration systems have combinations of pressures and temperatures that can and often do injure trained experienced technicians. It appears much safer than it actually is. This is more of a discussion than a recommended course of action.
Although getting a refrigeration system to work properly can be a challenge, the concept is actually incredibly simple. This is refrigeration 101 and just meant as a quick lesson.
There are 4 quadrants of operation. High and low pressure defined by the compressor and the expansion valve, everything after, the discharge of the compressor and before the expansion valve is high pressure(relative), everything after the expansion valve and to the low side of the compressor is low pressure. Everything after the condenser to the expansion valve is liquid, everything after the evaporator to the condenser is liquid. You end up with high pressure gas from the compressor to the condenser, high pressure liquid from the condenser to the TXV, low pressure liquid (actually a liquid gas mix) from the TXV to the evaporator, and a low pressure gas from the evaporator back to the compressor.
The only way to truly know what you have is with a pressure temperature chart for the refrigerant that you're using. Using water as an example, at atmospheric if I measure a water lines temperature if it is above well 212 F I know it is steam, if it is well below I know it is liquid, right around 212 it could be one or the other or a mixed state. 212 being the saturation temperature (ST) of water at sea level. At higher, or lower pressures the ST would be different, think radiator pressurization. Refrigerants are all the same.
Simple enough in theory, however, practically much more difficult, for example if you have a plugged dryer. In normal operation the pressure and temperature should be the same before and after the dryer, and the refrigerant should be high pressure liquid. If the dryer is plugged it can act as an expansion valve (an expansion valve being a controlled restriction), if this is the case the pressure and temperature will be lower after the filter dryer than before, the system will have unusual pressures and there will be poor AC capacity, the expansion valve is not deigned to meter a gas.
To Diagnose a refrigeration system, start with pressurizers as close to the compressor as possible, directly on the compressor is best. if the compressor is not working at all there will be no change in pressure. If the high pressure is lower than the low pressure the gauges are on the wrong ports. Once there is a difference in pressure using a PT chart find the saturation temp (ST) of the refrigerant from the chart, this should be done for both the high and low pressures.
With those STs in mind the actual measured temperatures should follow the quadrant described above,use a strap on thermometer to check. The compressor must be running when doing these checks.
Higher temperatures than the high pressure ST from the compressor to the condenser, lower than high pressure ST from the condenser to TXV, lower than the low pressure ST from the TXV to the evaporator, higher than the low pressure ST from the evaporator to the compressor.
If there is a temperature that doesn't make sense start there. the best indicator of low system charge being a temperature too close to ST after the condenser. I don't know what the values for automotive are, but in standard AC systems there is typically a minimum difference of 6-12 degrees. Then there is the example above on the plugged filter dryer.
If a TXV was plugged you would see higher pressures and associated temperatures on the high side, and lower pressures, and associated pressures on the low.
I've probably been all together too wordy, but there it is.
Good luck
I'm still confused by what you're saying.
1) What went to 190? Where you still feeding refrigerant when it went to 190?
2) Are you saying the pressures where 140 on the low and near 0 on the high? Or that the pressures on the high where cycling between 0 and 140? Either way my first thought is that the lines may be connected improperly. Where are you connecting your lines?
3) The sight glass on the dryer, ideally has few if any bubbles, primary use is to ensure a solid liquid column. As the oil is fully mixed in liquid refrigerant, you should not see oil moving across. If you are seeing oil it is more likely that there is no liquid at the sight glass.
First of all, I'm not recommending that anyone without training service their own AC systems. Refrigeration systems have combinations of pressures and temperatures that can and often do injure trained experienced technicians. It appears much safer than it actually is. This is more of a discussion than a recommended course of action.
Although getting a refrigeration system to work properly can be a challenge, the concept is actually incredibly simple. This is refrigeration 101 and just meant as a quick lesson.
There are 4 quadrants of operation. High and low pressure defined by the compressor and the expansion valve, everything after, the discharge of the compressor and before the expansion valve is high pressure(relative), everything after the expansion valve and to the low side of the compressor is low pressure. Everything after the condenser to the expansion valve is liquid, everything after the evaporator to the condenser is liquid. You end up with high pressure gas from the compressor to the condenser, high pressure liquid from the condenser to the TXV, low pressure liquid (actually a liquid gas mix) from the TXV to the evaporator, and a low pressure gas from the evaporator back to the compressor.
The only way to truly know what you have is with a pressure temperature chart for the refrigerant that you're using. Using water as an example, at atmospheric if I measure a water lines temperature if it is above well 212 F I know it is steam, if it is well below I know it is liquid, right around 212 it could be one or the other or a mixed state. 212 being the saturation temperature (ST) of water at sea level. At higher, or lower pressures the ST would be different, think radiator pressurization. Refrigerants are all the same.
Simple enough in theory, however, practically much more difficult, for example if you have a plugged dryer. In normal operation the pressure and temperature should be the same before and after the dryer, and the refrigerant should be high pressure liquid. If the dryer is plugged it can act as an expansion valve (an expansion valve being a controlled restriction), if this is the case the pressure and temperature will be lower after the filter dryer than before, the system will have unusual pressures and there will be poor AC capacity, the expansion valve is not deigned to meter a gas.
To Diagnose a refrigeration system, start with pressurizers as close to the compressor as possible, directly on the compressor is best. if the compressor is not working at all there will be no change in pressure. If the high pressure is lower than the low pressure the gauges are on the wrong ports. Once there is a difference in pressure using a PT chart find the saturation temp (ST) of the refrigerant from the chart, this should be done for both the high and low pressures.
With those STs in mind the actual measured temperatures should follow the quadrant described above,use a strap on thermometer to check. The compressor must be running when doing these checks.
Higher temperatures than the high pressure ST from the compressor to the condenser, lower than high pressure ST from the condenser to TXV, lower than the low pressure ST from the TXV to the evaporator, higher than the low pressure ST from the evaporator to the compressor.
If there is a temperature that doesn't make sense start there. the best indicator of low system charge being a temperature too close to ST after the condenser. I don't know what the values for automotive are, but in standard AC systems there is typically a minimum difference of 6-12 degrees. Then there is the example above on the plugged filter dryer.
If a TXV was plugged you would see higher pressures and associated temperatures on the high side, and lower pressures, and associated pressures on the low.
I've probably been all together too wordy, but there it is.
Good luck
07-12-2016, 12:54 AM
#7
Rennlist Member
Thread Starter
Thanks, but please see comments.
Steve,
I'm still confused by what you're saying.
1) What went to 190? Where you still feeding refrigerant when it went to 190?
2) Are you saying the pressures where 140 on the low and near 0 on the high? Or that the pressures on the high where cycling between 0 and 140? Either way my first thought is that the lines may be connected improperly. Where are you connecting your lines?
3) The sight glass on the dryer, ideally has few if any bubbles, primary use is to ensure a solid liquid column. As the oil is fully mixed in liquid refrigerant, you should not see oil moving across. If you are seeing oil it is more likely that there is no liquid at the sight glass.
First of all, I'm not recommending that anyone without training service their own AC systems. Refrigeration systems have combinations of pressures and temperatures that can and often do injure trained experienced technicians. It appears much safer than it actually is. This is more of a discussion than a recommended course of action.
Although getting a refrigeration system to work properly can be a challenge, the concept is actually incredibly simple. This is refrigeration 101 and just meant as a quick lesson.
There are 4 quadrants of operation. High and low pressure defined by the compressor and the expansion valve, everything after, the discharge of the compressor and before the expansion valve is high pressure(relative), everything after the expansion valve and to the low side of the compressor is low pressure. Everything after the condenser to the expansion valve is liquid, everything after the evaporator to the condenser is liquid. You end up with high pressure gas from the compressor to the condenser, high pressure liquid from the condenser to the TXV, low pressure liquid (actually a liquid gas mix) from the TXV to the evaporator, and a low pressure gas from the evaporator back to the compressor.
The only way to truly know what you have is with a pressure temperature chart for the refrigerant that you're using. Using water as an example, at atmospheric if I measure a water lines temperature if it is above well 212 F I know it is steam, if it is well below I know it is liquid, right around 212 it could be one or the other or a mixed state. 212 being the saturation temperature (ST) of water at sea level. At higher, or lower pressures the ST would be different, think radiator pressurization. Refrigerants are all the same.
Well -- not really, molecules of 134 are smaller and there are other differences, but I get what you mean, I think. But they are not interchangeable.
Simple enough in theory, however, practically much more difficult, for example if you have a plugged dryer. In normal operation the pressure and temperature should be the same before and after the dryer, and the refrigerant should be high pressure liquid. If the dryer is plugged it can act as an expansion valve (an expansion valve being a controlled restriction), if this is the case the pressure and temperature will be lower after the filter dryer than before, the system will have unusual pressures and there will be poor AC capacity, the expansion valve is not deigned to meter a gas.
To Diagnose a refrigeration system, start with pressurizers as close to the compressor as possible, directly on the compressor is best. if the compressor is not working at all there will be no change in pressure. If the high pressure is lower than the low pressure the gauges are on the wrong ports. This is not possible as the high is a different size from the low for this very reason. Once there is a difference in pressure using a PT chart find the saturation temp (ST) of the refrigerant from the chart, this should be done for both the high and low pressures.
You can only hook up manifold gauges at the ports Porsche put on the system. What are "pressurizers"?
With those STs in mind the actual measured temperatures should follow the quadrant described above,use a strap on thermometer to check. The compressor must be running when doing these checks.
Higher temperatures than the high pressure ST from the compressor to the condenser, lower than high pressure ST from the condenser to TXV, lower than the low pressure ST from the TXV to the evaporator, higher than the low pressure ST from the evaporator to the compressor.
If there is a temperature that doesn't make sense start there. the best indicator of low system charge being a temperature too close to ST after the condenser. I don't know what the values for automotive are, but in standard AC systems there is typically a minimum difference of 6-12 degrees. Then there is the example above on the plugged filter dryer.
If a TXV was plugged you would see higher pressures and associated temperatures on the high side, and lower pressures, and associated pressures on the low.
I've probably been all together too wordy, but there it is.
Good luck
I'm still confused by what you're saying.
1) What went to 190? Where you still feeding refrigerant when it went to 190?
2) Are you saying the pressures where 140 on the low and near 0 on the high? Or that the pressures on the high where cycling between 0 and 140? Either way my first thought is that the lines may be connected improperly. Where are you connecting your lines?
3) The sight glass on the dryer, ideally has few if any bubbles, primary use is to ensure a solid liquid column. As the oil is fully mixed in liquid refrigerant, you should not see oil moving across. If you are seeing oil it is more likely that there is no liquid at the sight glass.
First of all, I'm not recommending that anyone without training service their own AC systems. Refrigeration systems have combinations of pressures and temperatures that can and often do injure trained experienced technicians. It appears much safer than it actually is. This is more of a discussion than a recommended course of action.
Although getting a refrigeration system to work properly can be a challenge, the concept is actually incredibly simple. This is refrigeration 101 and just meant as a quick lesson.
There are 4 quadrants of operation. High and low pressure defined by the compressor and the expansion valve, everything after, the discharge of the compressor and before the expansion valve is high pressure(relative), everything after the expansion valve and to the low side of the compressor is low pressure. Everything after the condenser to the expansion valve is liquid, everything after the evaporator to the condenser is liquid. You end up with high pressure gas from the compressor to the condenser, high pressure liquid from the condenser to the TXV, low pressure liquid (actually a liquid gas mix) from the TXV to the evaporator, and a low pressure gas from the evaporator back to the compressor.
The only way to truly know what you have is with a pressure temperature chart for the refrigerant that you're using. Using water as an example, at atmospheric if I measure a water lines temperature if it is above well 212 F I know it is steam, if it is well below I know it is liquid, right around 212 it could be one or the other or a mixed state. 212 being the saturation temperature (ST) of water at sea level. At higher, or lower pressures the ST would be different, think radiator pressurization. Refrigerants are all the same.
Well -- not really, molecules of 134 are smaller and there are other differences, but I get what you mean, I think. But they are not interchangeable.
Simple enough in theory, however, practically much more difficult, for example if you have a plugged dryer. In normal operation the pressure and temperature should be the same before and after the dryer, and the refrigerant should be high pressure liquid. If the dryer is plugged it can act as an expansion valve (an expansion valve being a controlled restriction), if this is the case the pressure and temperature will be lower after the filter dryer than before, the system will have unusual pressures and there will be poor AC capacity, the expansion valve is not deigned to meter a gas.
To Diagnose a refrigeration system, start with pressurizers as close to the compressor as possible, directly on the compressor is best. if the compressor is not working at all there will be no change in pressure. If the high pressure is lower than the low pressure the gauges are on the wrong ports. This is not possible as the high is a different size from the low for this very reason. Once there is a difference in pressure using a PT chart find the saturation temp (ST) of the refrigerant from the chart, this should be done for both the high and low pressures.
You can only hook up manifold gauges at the ports Porsche put on the system. What are "pressurizers"?
With those STs in mind the actual measured temperatures should follow the quadrant described above,use a strap on thermometer to check. The compressor must be running when doing these checks.
Higher temperatures than the high pressure ST from the compressor to the condenser, lower than high pressure ST from the condenser to TXV, lower than the low pressure ST from the TXV to the evaporator, higher than the low pressure ST from the evaporator to the compressor.
If there is a temperature that doesn't make sense start there. the best indicator of low system charge being a temperature too close to ST after the condenser. I don't know what the values for automotive are, but in standard AC systems there is typically a minimum difference of 6-12 degrees. Then there is the example above on the plugged filter dryer.
If a TXV was plugged you would see higher pressures and associated temperatures on the high side, and lower pressures, and associated pressures on the low.
I've probably been all together too wordy, but there it is.
Good luck
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07-13-2016, 08:14 PM
#8
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Well -- not really, molecules of 134 are smaller and there are other differences, but I get what you mean, I think. But they are not interchangeable.
You can only hook up manifold gauges at the ports Porsche put on the system. What are "pressurizers"?
Pressurizers are a typo, should have been pressures.
My intent was not to infer that water and 134A are interchangeable, although interestingly with a vacuum based system water can be made to work as a refrigerant capable of working at AC temperatures. My intent was to draw a parallel with the pressurizing effect of the cooling system which raises the boiling point of the coolant. This is why removing the radiator cap on a hot engine is so dangerous. The coolant may be boiling or it may not be, when the radiator cap is removed the pressure in the system drops causing the boiling temperature to drop.
This sudden drop in boiling temperature not only hugely increases the likelihood that the engine temperature is now above the boiling point, but also increases the temperature difference between the engine and the boiling point increasing the energy available to boil refrigerant, thus the result is explosive boiling, or more technically evaporation. In a refrigeration system the action of the TXV is much like removing the radiator cap, the explosive boiling occurring in the evaporator.
I haven't had to diagnose problems on the AC of my 928's problems have been pretty obvious, however I have had to do so on my son's 944, and it had both high and low ports on the compressor and at least one of the pressure switches was also screwed onto a standard port. These in addition to the standard charging ports. I would expect the 928 to be similar, but can't say, next time I have the belly pan off I'll take a look.
Port sizes, high and low, should be the same, if they aren't then someone has likely added a port adapter. R134A has a different, quick type connector, than R12. This only for automobiles, R134A shares the same port as R12 and all other refrigerants on commercial equipment.
Shops when changing to 134a refrigerant, would add a fitting to adapt to the automotive R134A fitting, this would be a quick identifier of what refrigerant is in the system. The aforementioned 944 had these adapters, as does my 89 928, however if removed they have standard refrigerant ports underneath allowing the attachment of a normal refrigeration manifold. My more modern cars have the same R134 fitting throughout the system, but high and low ports are still the same. What is done for any specific retrofit or new car I can't comment on. The only cars I do are my own.
Good luck
You can only hook up manifold gauges at the ports Porsche put on the system. What are "pressurizers"?
Pressurizers are a typo, should have been pressures.
My intent was not to infer that water and 134A are interchangeable, although interestingly with a vacuum based system water can be made to work as a refrigerant capable of working at AC temperatures. My intent was to draw a parallel with the pressurizing effect of the cooling system which raises the boiling point of the coolant. This is why removing the radiator cap on a hot engine is so dangerous. The coolant may be boiling or it may not be, when the radiator cap is removed the pressure in the system drops causing the boiling temperature to drop.
This sudden drop in boiling temperature not only hugely increases the likelihood that the engine temperature is now above the boiling point, but also increases the temperature difference between the engine and the boiling point increasing the energy available to boil refrigerant, thus the result is explosive boiling, or more technically evaporation. In a refrigeration system the action of the TXV is much like removing the radiator cap, the explosive boiling occurring in the evaporator.
I haven't had to diagnose problems on the AC of my 928's problems have been pretty obvious, however I have had to do so on my son's 944, and it had both high and low ports on the compressor and at least one of the pressure switches was also screwed onto a standard port. These in addition to the standard charging ports. I would expect the 928 to be similar, but can't say, next time I have the belly pan off I'll take a look.
Port sizes, high and low, should be the same, if they aren't then someone has likely added a port adapter. R134A has a different, quick type connector, than R12. This only for automobiles, R134A shares the same port as R12 and all other refrigerants on commercial equipment.
Shops when changing to 134a refrigerant, would add a fitting to adapt to the automotive R134A fitting, this would be a quick identifier of what refrigerant is in the system. The aforementioned 944 had these adapters, as does my 89 928, however if removed they have standard refrigerant ports underneath allowing the attachment of a normal refrigeration manifold. My more modern cars have the same R134 fitting throughout the system, but high and low ports are still the same. What is done for any specific retrofit or new car I can't comment on. The only cars I do are my own.
Good luck