No ICE with Defrost on in Cold Weather?
#11
12-18-2009, 06:19 PM
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Re: No ICE with Defrost on in Cold Weather?
I have no basic disagreement with your statement.
"..or an evaporator temperature switch that cycles the compressor off when the evaporator becomes cold.."
I would revise that statement to say...
"..when the evaporator becomes too cold.."
The evaporator cannot long operate with exiting, downstream, airflow at or below freezing. Reaching that point can be due to the availability of liquid refrigerant or outside air entering the system with OAT at or below freezing.
Even the simplest of A/C compressor control systems make use of an evaporator vane surface temperature sensor to limit the operation of the compressor and therby prevention of condensate freezing and blocking system airflow entirely.
Some years ago, quite some years ago ('84 T-bird), refrigerant pressure switches were used to shut the compressor cycle off with an OAT as high as 47F. Nowadays so much reliance is placed on the ability to dehumidify the incoming FRESH airflow that systems typically do not shut down with declining OAT until less than or equal to 35F OAT is reached
"..or an evaporator temperature switch that cycles the compressor off when the evaporator becomes cold.."
I would revise that statement to say...
"..when the evaporator becomes too cold.."
The evaporator cannot long operate with exiting, downstream, airflow at or below freezing. Reaching that point can be due to the availability of liquid refrigerant or outside air entering the system with OAT at or below freezing.
Even the simplest of A/C compressor control systems make use of an evaporator vane surface temperature sensor to limit the operation of the compressor and therby prevention of condensate freezing and blocking system airflow entirely.
Some years ago, quite some years ago ('84 T-bird), refrigerant pressure switches were used to shut the compressor cycle off with an OAT as high as 47F. Nowadays so much reliance is placed on the ability to dehumidify the incoming FRESH airflow that systems typically do not shut down with declining OAT until less than or equal to 35F OAT is reached
#12
12-20-2009, 08:42 AM
Re: No ICE with Defrost on in Cold Weather?
I have no basic disagreement with your statement.
"..or an evaporator temperature switch that cycles the compressor off when the evaporator becomes cold.."
I would revise that statement to say...
"..when the evaporator becomes too cold.."
The evaporator cannot long operate with exiting, downstream, airflow at or below freezing. Reaching that point can be due to the availability of liquid refrigerant or outside air entering the system with OAT at or below freezing.
Even the simplest of A/C compressor control systems make use of an evaporator vane surface temperature sensor to limit the operation of the compressor and therby prevention of condensate freezing and blocking system airflow entirely.
Some years ago, quite some years ago ('84 T-bird), refrigerant pressure switches were used to shut the compressor cycle off with an OAT as high as 47F. Nowadays so much reliance is placed on the ability to dehumidify the incoming FRESH airflow that systems typically do not shut down with declining OAT until less than or equal to 35F OAT is reached
"..or an evaporator temperature switch that cycles the compressor off when the evaporator becomes cold.."
I would revise that statement to say...
"..when the evaporator becomes too cold.."
The evaporator cannot long operate with exiting, downstream, airflow at or below freezing. Reaching that point can be due to the availability of liquid refrigerant or outside air entering the system with OAT at or below freezing.
Even the simplest of A/C compressor control systems make use of an evaporator vane surface temperature sensor to limit the operation of the compressor and therby prevention of condensate freezing and blocking system airflow entirely.
Some years ago, quite some years ago ('84 T-bird), refrigerant pressure switches were used to shut the compressor cycle off with an OAT as high as 47F. Nowadays so much reliance is placed on the ability to dehumidify the incoming FRESH airflow that systems typically do not shut down with declining OAT until less than or equal to 35F OAT is reached
Willard, all I did was copy and paste that statement word for word from Keith Reinhardt. If you think he should have worded his statement differently just e-mail HIM and tell HIM.
Keith Reinhardt is an assistant professor of automotive technology at Southern Illinois University Carbondale in Carbondale, Ill. He holds a master's degree in educational administration and is an ASE-certified master automotive technician/paint and refinishing. His e-mail address is kvette@siu.edu.
GaryG - Happy Holidays ALL!
#13
12-25-2009, 12:10 AM
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Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: No ICE with Defrost on in Cold Weather?
Keith is making general statements, not FEH specific statements. The 2005 always runs the ice when in defrost. Later the programming was changed to allow ice shutdown when it is too cold fot a/c use. This is 32 degrees oat in a 2005 or 41 degrees evaporator temp. *measured countless times in my 2005
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