AC woes continue
07-28-2014, 12:44 PM
#17
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Thread Starter
Tossing in the towel. Dropping it off at the wrench in the am. Short of buying gauges, maybe more coolant, maybe pulling CCU and such...
I diagnosed and replaced 2 busted servos (Thx Tore). Beyond that I'm at diminishing returns to track down myself.
I diagnosed and replaced 2 busted servos (Thx Tore). Beyond that I'm at diminishing returns to track down myself.
07-28-2014, 01:02 PM
#18
JPS,
I believe your AC pressure switch is located near the top of evap box, picture below.
Locate the switch and carefully unplug its electrical connector.
Again, I believe, this is a 4 wire switch.
Locate, on the switch, terminals 1 and 4.
1 maybe be the corresponding white and orange wire.
Key off, using an ohm meter, check to see if you have continuity between
terminals 1 and 4 on the switch. If so, this would mean you have (provided we are
working with a good switch) at least 2.5 bar or 36 psi in the system in which case the
compressor clutch is allowed to engage (assuming, naturally that 2.5 is their design).
If you had a good set of service gauges this would be helpful at this time to see what
you got. If you don't have continuity, with the engine on, AC system running see if the
compressor clutch is engaged. If not, jumper the AC pressure switch connector terminals
between its corresponding pins 1 and 4. This should allow the AC clutch to engage.
This of course assumes I'm suggesting the correct terminals, and that terminals 2 and 3 do not need continuity in their design.
Let us know.
I believe your AC pressure switch is located near the top of evap box, picture below.
Locate the switch and carefully unplug its electrical connector.
Again, I believe, this is a 4 wire switch.
Locate, on the switch, terminals 1 and 4.
1 maybe be the corresponding white and orange wire.
Key off, using an ohm meter, check to see if you have continuity between
terminals 1 and 4 on the switch. If so, this would mean you have (provided we are
working with a good switch) at least 2.5 bar or 36 psi in the system in which case the
compressor clutch is allowed to engage (assuming, naturally that 2.5 is their design).
If you had a good set of service gauges this would be helpful at this time to see what
you got. If you don't have continuity, with the engine on, AC system running see if the
compressor clutch is engaged. If not, jumper the AC pressure switch connector terminals
between its corresponding pins 1 and 4. This should allow the AC clutch to engage.
This of course assumes I'm suggesting the correct terminals, and that terminals 2 and 3 do not need continuity in their design.
Let us know.
07-29-2014, 11:38 PM
#19
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Thx. I dropped it off at the wrench this am. I might take another look at all the above if they come back saying a basic flush didn't solve the problem.
07-30-2014, 07:07 AM
#20
"a basic flush" ???
Unless you grenaded your compressor no one should be flushing anything.
A flush would require quite a bit of labor; lots of things to disassemble and re-assemble.
The first thing you do is attach gauges and check the static pressure to insure there is sufficient refrigerant for the low side cut off switch function to allow the compressor clutch to engage. If there is sufficient pressure, and nothing simple like a blown fuse, you test the pressure switch.
Unless you grenaded your compressor no one should be flushing anything.
A flush would require quite a bit of labor; lots of things to disassemble and re-assemble.
The first thing you do is attach gauges and check the static pressure to insure there is sufficient refrigerant for the low side cut off switch function to allow the compressor clutch to engage. If there is sufficient pressure, and nothing simple like a blown fuse, you test the pressure switch.
07-30-2014, 02:27 PM
#21
Drifting
"a basic flush" ???
Unless you grenaded your compressor no one should be flushing anything.
A flush would require quite a bit of labor; lots of things to disassemble and re-assemble.
The first thing you do is attach gauges and check the static pressure to insure there is sufficient refrigerant for the HIGH SIDE low pressure cut off switch function to allow the compressor clutch to engage. If there is sufficient pressure, and nothing simple like a blown fuse, you test the pressure switch.
Unless you grenaded your compressor no one should be flushing anything.
A flush would require quite a bit of labor; lots of things to disassemble and re-assemble.
The first thing you do is attach gauges and check the static pressure to insure there is sufficient refrigerant for the HIGH SIDE low pressure cut off switch function to allow the compressor clutch to engage. If there is sufficient pressure, and nothing simple like a blown fuse, you test the pressure switch.
07-30-2014, 03:25 PM
#22
LOL !
I just love it when they quote me.
Yes. Doctor West. Just so you don't get all twisted here:
on a TEV system you can have a switch that measures positive pressures on the high side, and if you like you can have a switch that measures positive pressures on the low side.
In context of the forum tree and its thread.
And, thank you once again for contributing useful information for the readers.
There are:
known knowns
known unknowns
unknown knowns
unknown unknowns
I just love it when they quote me.
Yes. Doctor West. Just so you don't get all twisted here:
on a TEV system you can have a switch that measures positive pressures on the high side, and if you like you can have a switch that measures positive pressures on the low side.
In context of the forum tree and its thread.
And, thank you once again for contributing useful information for the readers.
There are:
known knowns
known unknowns
unknown knowns
unknown unknowns
07-31-2014, 02:13 PM
#23
Drifting
LOL !
I just love it when they quote me.
Yes. Doctor West. Just so you don't get all twisted here:
on a TEV system you can have a switch that measures positive pressures on the high side,
"...and if you like you can have a switch that measures positive pressures on the low side..."
And since that would be a totally USELESS function may I assume no such configuration exists.
In context of the forum tree and its thread.
And, thank you once again for contributing useful information for the readers.
There are:
known knowns
known unknowns
unknown knowns
unknown unknowns
I just love it when they quote me.
Yes. Doctor West. Just so you don't get all twisted here:
on a TEV system you can have a switch that measures positive pressures on the high side,
"...and if you like you can have a switch that measures positive pressures on the low side..."
And since that would be a totally USELESS function may I assume no such configuration exists.
In context of the forum tree and its thread.
And, thank you once again for contributing useful information for the readers.
There are:
known knowns
known unknowns
unknown knowns
unknown unknowns
07-31-2014, 05:42 PM
#24
Doctor West,
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp. Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed. And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems. And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp. Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed. And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems. And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.
07-31-2014, 07:05 PM
#25
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Thread Starter
Back to the point of the post, I had them drain and put in new coolant, still didn't work. 
I told them to poke around a couple hours and see what they found. Said a vacuum line was off somewhere...not sure where. I'll get details and let you know here.
I told them to poke around a couple hours and see what they found. Said a vacuum line was off somewhere...not sure where. I'll get details and let you know here.
08-01-2014, 01:57 PM
#26
Drifting
Doctor West,
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
Sorry Kuehl, but I'm forced to say BS to that. With the low pressure switch installed on the low side you would need a circuit "latch" function to keep the compressor engaged since once it starts since it would DRAMATICALLY lower the low side pressure. So you couldn't use the same cut-out setting on the low side sensing as you would/could on the high side.
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp.
Just as I have said, a low pressure cutout on the high side could have a cutout pressure of ~50 PSI, whereas on the low pressure side it must be BELOW any normal operation low side pressure level.... and in your opinion just how low might that be?
Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed.
And just what/which normally operating system would have a low side pressure that low absent the compressor being already engaged? And if it's that low PRIOR to compressor engagement then isn't the refrigerant charge to low in your judgment?
And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems.
Oh, sorry, I guessed I missed the post wherein the subject matter changed from Porsche factor systems to the RV type.
And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
Sorry Kuehl, but I'm forced to say BS to that. With the low pressure switch installed on the low side you would need a circuit "latch" function to keep the compressor engaged since once it starts since it would DRAMATICALLY lower the low side pressure. So you couldn't use the same cut-out setting on the low side sensing as you would/could on the high side.
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp.
Just as I have said, a low pressure cutout on the high side could have a cutout pressure of ~50 PSI, whereas on the low pressure side it must be BELOW any normal operation low side pressure level.... and in your opinion just how low might that be?
Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed.
And just what/which normally operating system would have a low side pressure that low absent the compressor being already engaged? And if it's that low PRIOR to compressor engagement then isn't the refrigerant charge to low in your judgment?
And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems.
Oh, sorry, I guessed I missed the post wherein the subject matter changed from Porsche factor systems to the RV type.
And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.
So, tell us, which of your answers/statements can Op (or myself) rely on to troubleshoot/understand the thread subject matter, air-cooled Porsche 911 A/C systems?
08-01-2014, 02:05 PM
#27
Drifting
Doctor West,
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
Does the following have any importance with respect to the thread topic?
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
Anyone, including yourself, ever actually done this to an air-cooled 911 factory A/C system? Or should Op consider it completely off-topic?
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp. Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed. And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems. And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.
When you quote something in a thread and then toss in your own cabbage it becomes a confusing salad.
The stock 993/964 has its "low, high" combination switch located in the high side of the refrigerant circuit. The low side function is to determine if there is sufficient refrigerant in the system before it allows the compressor clutch to engage. This location point is common in expansion valve (aka TXV, TEV) systems, meaning its past the compressor outlet port, aka high side.
Does the following have any importance with respect to the thread topic?
If you want, you can put a pressure switch on the low side that cuts out the compressor when the system pressures drop below xx value. We've done it before but its easier to keep that function in one switch on the high side to reduce the number of components.
Anyone, including yourself, ever actually done this to an air-cooled 911 factory A/C system? Or should Op consider it completely off-topic?
With regard to you postulating "you can't have a low pressure cut-out switch on the low side unless you limit its function to only A/C starts post hours of non-use." , I disagree. When the system is equalized (happens shortly after the system shuts down), the static pressure can range from 60 to 80 psi nominal depending upon the volume of the system and the ambient temp. Hence a low side pressure switch that makes contact at 20 psi (for example) will allow the clutch to engage when needed. And when the system is running, should the low side drop below 20 psi it will shut off the compressor as well; this is a common design in variable displacement compressors and orifice tube (non TEV) systems. And, said being in a TEV system that is operating normally, if you have such a switch on the low side, if the system pressures drop below 20 psi or whatever value switch you place there, the compressor would disengage. When would this be helpful? If you wanted a design that cuts out when the evaporator core reaches a near corresponding temperature/pressure point.
So, unless you just want to continue to "boil the ocean" here, please provide some positive, factual, and meaningiful advise for Opey.