A/C Too Cold
07-22-2002, 08:13 PM
#1
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A/C Too Cold
I recently migrated from R12 to R134A. Replaced expansion valves, dryer and bunch of o-rings. I know I shouldn't complain, but, the temp is dropping to ~20 degrees at times at the center vent and will not respond to the slider of the AC head unit. I have to shut down the AC to prevent a freeeze over.
I ruled out the head unit by using the one out of my '85.
Assuming the temperature probe is correct, what could make the AC ignore the controller?
Could the AC compressor be at fault?
TIA
I ruled out the head unit by using the one out of my '85.
Assuming the temperature probe is correct, what could make the AC ignore the controller?
Could the AC compressor be at fault?
TIA
07-22-2002, 10:20 PM
#2
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Well the nerve of complaining about a freezer in the car. Next you'll want a defroster for it too. Just Kidding.
Seriously now,
For the temperature to drop to minus 20 degrees F. One safety is not working properly. That would be the freeze stat. The freeze stat has a cut out point above 32 F to prevent the evap coil from freezing into a block of ice. It appears yours is not cutting out. You are correct the evap coil is starting to freeze the condensate on the coil, hence the abnormally cold air.
It sounds like an insufficient supply of subcooled liquid refrigerant at the txv.
Are you able to read the high and low side readings of your system? (I am presuming you have or know someone with a set of guages)
Now onward. You said your a/c system is now running on R134a, correct. Did you have someone perform the work of the retro fit? Do you know by weight the refrigerant charge of the system after the retro-fit?
John D.
'85 928 Auto, Black
Seriously now,
For the temperature to drop to minus 20 degrees F. One safety is not working properly. That would be the freeze stat. The freeze stat has a cut out point above 32 F to prevent the evap coil from freezing into a block of ice. It appears yours is not cutting out. You are correct the evap coil is starting to freeze the condensate on the coil, hence the abnormally cold air.
It sounds like an insufficient supply of subcooled liquid refrigerant at the txv.
Are you able to read the high and low side readings of your system? (I am presuming you have or know someone with a set of guages)
Now onward. You said your a/c system is now running on R134a, correct. Did you have someone perform the work of the retro fit? Do you know by weight the refrigerant charge of the system after the retro-fit?
John D.
'85 928 Auto, Black
07-23-2002, 12:28 AM
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dozman, the vehicle was charged at 80% of the r12 spec. sucked down and recharged to the 80%. just to make sure of no issues or mistakes. the presures at idle and the temp at idle are not even close to this 20 degree mark. other than evap temp sensor not shutting down at proper time and or temp i cant think of any other cause. but if you gots a clue i would love to here it. joel
07-23-2002, 09:37 AM
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Sounds like two problems.
The thermostatic expansion valve should try to hold the evaporator temp close to 32 deg F - sounds as if yours is from a freezer instead of a refrigerator.
The anti-freeze switch should cut the compressor off when the evaporator gets too cold - sounds as if yours isn't doing that.
My impression is that the temp circuit tries to hold the specified interior temp EXCEPT at the estreme ends - in other words, at the extreme left end, the system will go to full cold regardless of the inerior temp, at the right end it will go to full hot regardless of the interior temp.
Are you recovered from your visitor? ;-)
The thermostatic expansion valve should try to hold the evaporator temp close to 32 deg F - sounds as if yours is from a freezer instead of a refrigerator.
The anti-freeze switch should cut the compressor off when the evaporator gets too cold - sounds as if yours isn't doing that.
My impression is that the temp circuit tries to hold the specified interior temp EXCEPT at the estreme ends - in other words, at the extreme left end, the system will go to full cold regardless of the inerior temp, at the right end it will go to full hot regardless of the interior temp.
Are you recovered from your visitor? ;-)
07-23-2002, 10:28 AM
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hi wally.
i think any expansion valve is capable of freezer status. i agree that the freeze switch is at falt and am wondering if anyone in the list ever figured out the gm part number on this switch. would like to see the price difference between porsch and gm on this part. as for control of temp i think its time to run tests on all temp sensors. i found on joann,s ac the temp motor stuck toward hot. the ambiant temp sensor wire was broken and twisted together. after testing sensor and repairing the wire the temp door motor functioned normally. using my freon identifier after her self made retro i found it still had r12 8% 134 79% hc,s 11%. hc,s? does that indicate the cooler behind the air cleaner is leaking into system? i have found on other ac systems that the temp sensors are the rule for good control. have found very few bad head units, just misinformed ones. thanks for the input. as to the visit, it was pleasant. shes a nice person. her car ran the gammit of issues though. the short in the dome lite circut was tough to find. the diagram didnt quite match her vehicle. finally found wire touching on parking brake lever bracket. the wire went to the rear hatch switch. by the way, do you know off hand if the rear hatch motor park position is internal to the motor or a relay timed cycle. thanks again, joel
i think any expansion valve is capable of freezer status. i agree that the freeze switch is at falt and am wondering if anyone in the list ever figured out the gm part number on this switch. would like to see the price difference between porsch and gm on this part. as for control of temp i think its time to run tests on all temp sensors. i found on joann,s ac the temp motor stuck toward hot. the ambiant temp sensor wire was broken and twisted together. after testing sensor and repairing the wire the temp door motor functioned normally. using my freon identifier after her self made retro i found it still had r12 8% 134 79% hc,s 11%. hc,s? does that indicate the cooler behind the air cleaner is leaking into system? i have found on other ac systems that the temp sensors are the rule for good control. have found very few bad head units, just misinformed ones. thanks for the input. as to the visit, it was pleasant. shes a nice person. her car ran the gammit of issues though. the short in the dome lite circut was tough to find. the diagram didnt quite match her vehicle. finally found wire touching on parking brake lever bracket. the wire went to the rear hatch switch. by the way, do you know off hand if the rear hatch motor park position is internal to the motor or a relay timed cycle. thanks again, joel
07-23-2002, 10:37 AM
#6
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[quote]Originally posted by WallyP:
<strong>Sounds like two problems.
The thermostatic expansion valve should try to hold the evaporator temp close to 32 deg F - sounds as if yours is from a freezer instead of a refrigerator.
The anti-freeze switch should cut the compressor off when the evaporator gets too cold - sounds as if yours isn't doing that.
My impression is that the temp circuit tries to hold the specified interior temp EXCEPT at the extreme ends - in other words, at the extreme left end, the system will go to full cold regardless of the interior temp, at the right end it will go to full hot regardless of the interior temp.
</strong><hr></blockquote>
Further info: Swapped out the AC controller from my '85 and got the same behavior that consisted of dropping the temp to less than 30 degrees. The slider was set to 70-75 degrees. I had hoped that it was the controller. But, unless they are both broken, no dice.
Wally, I have the write up you handed out at SITM, but the section on temperature regulation is missing.
Anyway, The temp is not being regulated, the AC is probably always on and the fan in the sensor is working.
According to a post I saw here on Rennlist, a sensor 'short' pushes the temp to cold. I'll have to look at that.
Also, in another post on Nichol's site, a broken evaporator probe would cause the AC not to work. So, I am thinking that the probode may have become dislodged when I cleaned the evaporator core during the retrofit. Is that sensor the connected to the yellow wire coming out of the blower moter housing near the expansion valve?
But, that does not explain why the temp is not being regulated, right?
Anyway, I appreciate the help. Thanks.
<strong>Sounds like two problems.
The thermostatic expansion valve should try to hold the evaporator temp close to 32 deg F - sounds as if yours is from a freezer instead of a refrigerator.
The anti-freeze switch should cut the compressor off when the evaporator gets too cold - sounds as if yours isn't doing that.
My impression is that the temp circuit tries to hold the specified interior temp EXCEPT at the extreme ends - in other words, at the extreme left end, the system will go to full cold regardless of the interior temp, at the right end it will go to full hot regardless of the interior temp.
</strong><hr></blockquote>
Further info: Swapped out the AC controller from my '85 and got the same behavior that consisted of dropping the temp to less than 30 degrees. The slider was set to 70-75 degrees. I had hoped that it was the controller. But, unless they are both broken, no dice.
Wally, I have the write up you handed out at SITM, but the section on temperature regulation is missing.
Anyway, The temp is not being regulated, the AC is probably always on and the fan in the sensor is working.
According to a post I saw here on Rennlist, a sensor 'short' pushes the temp to cold. I'll have to look at that.
Also, in another post on Nichol's site, a broken evaporator probe would cause the AC not to work. So, I am thinking that the probode may have become dislodged when I cleaned the evaporator core during the retrofit. Is that sensor the connected to the yellow wire coming out of the blower moter housing near the expansion valve?
But, that does not explain why the temp is not being regulated, right?
Anyway, I appreciate the help. Thanks.
07-23-2002, 11:21 PM
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Uhhh...
Your cold temps are making me sick!
Just kidding...
I've fiddled with my system and still cannot get the Freeze Switch to activate. New hoses, dryer, Compressor, thermal exansion valves. Geez...
I guess I may look at the condensor next and (shudder) then the evaporator.
Currently, with the car at 2K rpms for 10minutes, with blower set on 2, I get 45 dF air at both the center and rear vents on 85 dF ambient.
Doens't help the car is black on black I know - but still...it should be better than this I would think.
<img src="confused.gif" border="0">
Your cold temps are making me sick!
Just kidding...
I've fiddled with my system and still cannot get the Freeze Switch to activate. New hoses, dryer, Compressor, thermal exansion valves. Geez...
I guess I may look at the condensor next and (shudder) then the evaporator.
Currently, with the car at 2K rpms for 10minutes, with blower set on 2, I get 45 dF air at both the center and rear vents on 85 dF ambient.
Doens't help the car is black on black I know - but still...it should be better than this I would think.
<img src="confused.gif" border="0">
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07-24-2002, 12:15 AM
#8
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[quote]Originally posted by Jay Wellwood:
<strong>Uhhh...
Currently, with the car at 2K rpms for 10minutes, with blower set on 2, I get 45 dF air at both the center and rear vents on 85 dF ambient.
</strong><hr></blockquote>
Dear confused,
Have you tried the test without the rear AC on. I have rear AC but don't run it because the overall temp will drop quite a bit. Joel thinks the rear temp probe is faulty making the servo shut off freon to the rear AC. Is 45 degrees all that bad? Especially, with the rear AC on. Personally, I'd prefer your results to my 20 degree situation.
-Tib
<strong>Uhhh...
Currently, with the car at 2K rpms for 10minutes, with blower set on 2, I get 45 dF air at both the center and rear vents on 85 dF ambient.
</strong><hr></blockquote>Dear confused,
Have you tried the test without the rear AC on. I have rear AC but don't run it because the overall temp will drop quite a bit. Joel thinks the rear temp probe is faulty making the servo shut off freon to the rear AC. Is 45 degrees all that bad? Especially, with the rear AC on. Personally, I'd prefer your results to my 20 degree situation.
-Tib
