Wintertime A/C Tips....

If you live north of the snowline, as I do, Seattle area, now would be a good time to think serious about disabling your A/C compressor. On my RX300 I simply unplug the refrigerant pressure sensor switch just in front of the radiator. In older models I always unplugged the A/C compressor clutch circuit. WHY ??? Most modern day automotive A/C systems, most especially those of the automatic climate control variety, will automatically engage the A/C system to help dehumidify the incoming airstream (you wouldn't DARE be in recirulate at this point!). At moderately cool outside temperatures, down to about 45F, this can often be a great advantage. But below these temperatures the efficiency of the A/C to dehumidify the incoming airstream declines precipetously, until at just above freezing, ~35F, there is NO dehumidification capability whatsoever. With outside temperatures below 45F your system should never be in recirculate, and should ALWAYS remain in the mode wherein outlet airflow is significantly heated and routed through the footwell outlet ducts, with a portion bled off to the windshield defrost/defog/demist ducts. This latter air flow is there, by factory design, to help (hopefully) keep the interior of the windshield above dewpoint, the point at which condensation begins to form. If you have a manually operated system then it will be up to you to remember to monitor the outside temperature and be sure the system has the proper airflow routing, footwell only, as the outside temperature declines. If you happen to have one of the automatic climate control systems designed or manufactured by NipponDenso in Japan, or Denso USA, in the US, Toyota and Lexus for instance, it will be "biased" toward "cooling" mode (airflow outlet to the face and upper body) regardless of COLD outside temperatures and your personal discomfort due to radiant "cooling" from the COLD surrounding landscape. Again, it will be up to you, as the driver and therefore "protector" of yourself and your passengers, to be extremely vigilent and ALWAYS over-ride the system from "automatic" outlet airflow control mode, to footwell and defrost/defog/demist mode manually when outside temperatures decline below 45F. Now. If the outside temperature is below 45F and IF the interior of your windshield beings to fog over, even ever so slightly, you need to take IMMEDIATE action. 1. Turn the temperature control all the way UP, to MAX HEAT. 2. Turn the system Blower all the way to MAXIMUM speed. 3. THEN.... Change the system outlet airflow mode to defrost/defog/demist. So, why did this happen, why did the windshield start to fog over? First, let's assume you followed the above instructions and the system was in heating mode, footwell and defrost/defog/demist airflow mode, and NOT IN RECIRCULATE! At, say, 65MPH on a really cold day your windshield is being quite thoroughly chilled with the COLD airstream impinging on the outside at 65MPH even though there is a significant level of warming airflow from the system flowing its interior surface. But now you just picked up two sweaty and wet snow skiers and you're headed back down the mountain. Or you were headed up to the slopes and your passengers became stressed out (sweating profusely) due to the ice and snow covered roadbed and the sometimes unavoidable side-slipping of the vehicle. Moisture = higher humidity + a cool windshield surface = condensation. Cracking a rear window slightly will almost always help move the cool dry air through the vehicle. If you have not disabled your A/C for wintertime driving there may be yet another cause for the windshield fogging over. Your A/C system was running but now isn't. 1. It may have shut down of it's own accord, automatically, a few moments ago, due to declining outside temperatures, 35F or below. Many modern systems will do this automatically, with no warning or obvious indication to the operator. 2. You may have just previosuly used the defrost/defog/demist mode, unaware that this mode automatically activates the A/C system to assist in dehumidification. Once you return the system to normal operation the A/C will shutdown provided you have used the control functionality to turn it off. 3. You may have just noticed that the temperatures have declined and manually turned off the useless A/C. But why would any of these actions lead to windshield fogging to the point of being a real safety issue?? Long story, but first a short version. When the A/C is operating it will almost always "gather" airborne water vapor onto the evaporator vanes. As more and more moisture accumulates it will eventually become dropletts large enough that gravity overcomes viscosity and then run down the face of the evaporator and out the drain provided for this purpose. When the A/C compressor is first shut down the temperature of the evaporator surfaces will begin to rise. And remember ALL system inlet airflow, fresh and recirculated, comes through the evaporator. So that thin film of moisture, the film of moisture that had not yet gained enough mass to overcome viscosity, will begin to evaporate into the atmosphere within the passenger cabin. BINGO! Cold windshield, high atmospheric humidity. The windshield begins to fog over! Modern day exacerbating circumstances... 1. New, less efficient refrigerant. With the advent of the use of the new less efficient refrigerants automotive designers were fored to come up with ways to make up for the loss of efficiency. The most obvious way, and the one most often chosen, was to make the evaporator itsself a lot more efficient. The evaporator in my 1984 T-bird had about 2500 square inches of evaporator cooling surface. The one in the newer vehicles is more typically in the range of 10,000 square inches. More evaporator surface area = more moisture left over to humidify the passenger cabin once the A/C is turned off. 2. Reduce the cabin atmosphere's "exhaust" outflow. On a minute by minute basis, the less "conditioned" air that leaves the controlled environment the less incoming airflow that must be cooled. 3. Lower the system blower speed. The slower the airflow moves through the evaporator vanes the more "heat" it gives up. A lower blower speed also results in even less exhaust outflow due to blower induced pressure differentials. The Lexus car series is very well insulated for sound deadening and wind noise. MY 92 LS400, in fully automatic mode, could be using recirculate for 90% of the flow in the winter or summer, with the indicator light showing "fresh" mode. My 2001 C4 has a toggle switch in the console glove box that opens the A/C compressor circuit.

Am I missing something here? There is a button for A/C on or off and the temperature and fan can be regulated w/o the use of the A/C. So not being an engineer, what am I missing????

Regardless of what you do manually to turn the A/C off, it will still come on automatically when you use the defrost/defog/demist mode. And the danger comes when you go back to normal operation and the A/C is automatically returned to "your" off state.

Oh!

I am having trouble understanding the temp control in my Pepper. I think I understand the issue. First there is no on/off for the refrigerant. I had a hard time understanding why the AC would come on when the outside temp is 68 degrees and I set the inside to 80 degrees when set on AUTO. Additionally, When put on ECON (I thought AC turned off) the AC still came on. Exasperating.. I think I'll just disconnect - the hell with it....