defogger/defrost only blows hot air
02-23-2012, 11:35 PM
#1
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defogger/defrost only blows hot air
Normal operation I assume?
AC works fine but even if the temp is set to low, when I press the front defrost/defogger button, it only blows hot air.
AC works fine but even if the temp is set to low, when I press the front defrost/defogger button, it only blows hot air.
02-26-2012, 03:09 PM
#2
Drifting
HOT airflow will ALWAYS defog/demist the windshield interior surface whereas the use of the A/C to dehumidify the system airflow is determined by mother nature. With the OAT below about 45-50F the incoming air Rh is rarely high enough to quickly result in a significant level of dehumidification. If the OAT is below ~34F the A/C compressor will be COMPLETELY disabled.
The HOT airflow, additionally, will HEAT the windshield surface thereby reducing the potential for re-occurrence of windshield condensation significantly.
My '01 C4 has switch mounted on the back wall of the console glove box with which I can disable the A/C compressor, open the A/C clutch circuit, throughout the cool/cold weather season.
There is no IMMEDIATE harm in the use of the A/C as an axillary defog/demist capability, it might actually help if the Rh is relative high.
But beware....CAUTION.
If the A/C is subsequently cycled OFF, as is usually the case, the condensate just previously condensed onto the ~10,000 square inches of COLD evaporator vane surface area will now be FREE to evaporate into the incoming airflow. That often results, as the cabin Rh rises, in a quick re-occurrence of the windshield fogging episode.
Best to NEVER rely on the A/C except for actual cooling need or initial cabin cooldown.
The HOT airflow, additionally, will HEAT the windshield surface thereby reducing the potential for re-occurrence of windshield condensation significantly.
My '01 C4 has switch mounted on the back wall of the console glove box with which I can disable the A/C compressor, open the A/C clutch circuit, throughout the cool/cold weather season.
There is no IMMEDIATE harm in the use of the A/C as an axillary defog/demist capability, it might actually help if the Rh is relative high.
But beware....CAUTION.
If the A/C is subsequently cycled OFF, as is usually the case, the condensate just previously condensed onto the ~10,000 square inches of COLD evaporator vane surface area will now be FREE to evaporate into the incoming airflow. That often results, as the cabin Rh rises, in a quick re-occurrence of the windshield fogging episode.
Best to NEVER rely on the A/C except for actual cooling need or initial cabin cooldown.
02-26-2012, 03:37 PM
#3
Drifting
But only for the more clever automotive climate control design engineers..which EXCLUDES the NipponDenso and/or Denso US engineering IDIOTS.
When a driver actuates the defrost/defog/demist mode of the climate control system a reasonably intelligent design would operate as if the there is the most DIRE defog/demist need, presume that for whatever reason forward visibility is severely compromised.
NipponDenso, Denso US, automatic climate control designs, once found only in Asian built products, now seem to also dominate the US automotive market. These designs are TERRIBLY, even HORRIBLY flawed insofar as the need to most QUICKLY defog/demist the windshield interior surface once the cabin temperature is within or nearby the selected temperature setpoint.
After years of trying to deal with my '92 LS400's propensity for SUDDENLY/SPONTANEOUSLY fogging over the interior windshield surface without warning. I finally took the climate control computer apart and modified it's defrost/defog/demist mode operation such that with the PB actuation of the defog/demist mode then FULL HEAT and FULL blower speed is called for INSTANTLY.
