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Keeping warm in the car.

Saturday, 5 February, 2011

Through my recent automobile-shopping experience, and during the recent aberrant weather I am aware of a mythology so pervasive in Texas it must be projected upon young people by some authority figure. This particular myth involves the idea that automobiles with an internal-combustion engine (that is, your car) generate cabin heat through electric resistance coils, like an electric range. It is therefore confounding to people in my world that an automobile does not generate heat immediately in 20F/-7C conditions with strong prairie winds.

I suspect most of you have at least a general idea of how the cabin-heating system works in a modern (read: “built after World War II”) automobile. Specifically, when activated, the engine coolant flows through an auxiliary radiator or “heater core” which radiates heat into the cabin. The heat radiating from the heater core may be encouraged through the use of fans built into the automobile for this purpose. This system is so robust it has remained fundamentally unchanged for over seventy years.

Given the urgency of this issue at the moment, I shall now describe a method through which one may have maximum cabin heat in the least amount of time. This process may be used to warm the interior of your car to assist in removing ice or snow from the windows. This tutorial assumes you have a vehicle produced since 1960 which is parked outside. The weather conditions are quite cold and the windows opaqued with ice. Furthermore, we assume you do not have “de-icing fluid” in your windshield-washer-fluid reservoir, and is therefore useless.

If you have a vehicle with an HVAC system that is controlled through a computer or a fully electronic interface, it is actually doing all of this on its own so you may as well move on.

The two varieties of air-cooled vehicles sold on this continent within living memory operate using similar principles, although without fluid and using forced air. The method described below may also be used, even if the controls are very different, if you drive a classic Volkswagen or Chevrolet Corvair.

Depending upon the make and era of your vehicle, the HVAC system may be operated with either dials, slider controls or a combination of the two. The settings are the same. Frustratingly, on some Ford and GM vehicles the critical “recirculation” setting is labeled “Max AC”. Certain GM and Chrysler vehicles have no recirculation setting and “Max AC” activates the air conditioner which should remain switched off.

Although cars of recent manufacture, since 1993 or so, use the air-conditioning system to demist windows in humid conditions, this has no effect on de-icing. Some GM and Mercedes-Benz vehicles built before 1980 have a specific “De-ice” setting which projects heat directly to the windshield. I miss that, and bench seats. If you have “De-ice” use it only after heat is flowing into the cabin. Rear-window defrosters and wing or exterior rear-view mirror de-icers are electric and should only be switched on once heat is flowing into the cabin.

Before starting the engine, make certain the HVAC controls are set as follows:

  • Fans off, or low
  • 100% cold
  • Air flow to off preferred, or set to air flow to dash and floor

Start the engine. Then sit there. If you live in a part of the world where they distribute “summer” batteries, essentially anyplace in the south or southwest, you may turn on the radio although not a media player, CD, etc. Do not switch on anything else until heat is flowing into the cabin.

The object here is to let the engine warm in order to provide heat to the HVAC system. Cold and very cold conditions are harmful to vehicles prepared for weather over 100F. Although the car will warm more quickly if moving or “under load”, the possibility of damage is such that you really should just sit there until everything is up to operating temperature.

In fact, this isn’t the best time to start scraping ice off windows, just sit there. If your vehicle has daytime running lights, keep the hand brake or parking brake engaged.

If you must move as soon as possible, do not do so until the engine-temperature gauge moves a little. However, the ideal situation is to allow the engine to warm to full operating temperature. That is: the needle on the engine-temperature gauge is pointing where it usually does when the car is in use.

When the engine is fully warm, and only when the engine is fully warm:

  • move the air-flow setting from its present position to “air-flow to floor”
  • move the temp indicator to 100% hot
  • fans remain off

If the air temperature is low enough, you may see the engine temperature drop as coolant flows into the heater core. This does not indicate a problem. Eventually, two-or-three minutes in a car with an engine under two liters, up to seven-to-ten minutes with a larger engine, you will feel heat radiating from the floor. For some reason “American” cars take longer.

Once you feel heat radiating from the floor, switch the fans to the setting just below maximum. If you have four fan speeds, select the third. If you have a “Max AC” setting that does not engage the air-conditioning set the air flow to “Max AC”. Otherwise, engage recirculation. This recycles and rewarms the air in the cabin.

Yes, there is some outside air let inside while recirculating cabin air. You need not worry about suffocation or anything. Some cars with a button to recirculate air will automatically disengage the mode if humidity rises over 70% or so. If recirculation switches itself off, don’t worry about it.

Although you have wasted fifteen minutes or so, the cabin is quickly warming along with the windows. Warm windows assist with the de-iceing or scraping process. If you have a rear-window defroster, wing mirror de-icers or heated seats you may turn them on now. Before exiting the cabin to address manual de-icing or scraping set the air flow to “air flow to floor + defrost”. If you have a rare “de-ice” setting on your HVAC, use it. I assure you this will be the least painful de-icing you have ever experienced. When you reenter the cabin the car may be as warm as 80F/28C, and you’ll want that.
Please note that some jurisdictions consider a fully secured automobile which happens to be switched on as “unoccupied” and utilize this technicality for opportunistic fining. Know the law. Do not fall prey to this abuse. If you live in such an area, warm the car, switch it off, then scrape.

It is likely that the air temperature has fallen significantly just before the first snow. As with any sudden change of temperature, check the air pressure in your tires. Colder temperatures can cause the air pressure within your tires to drop twenty percent or more. Don’t guess. Be certain. Don’t depend on the TPMS. Check your tire pressure. You just might need all the traction you have coming to you.

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