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Diagnosing heater issues
On The Road AgainJanuary 18, 2012 | 4,327 views | Post a comment
It’s that time of year again when we try out the heater in old Betsy and hope for the best. Most heating systems have remained relatively simple over the years, with only the addition of blend doors and climate control systems to complicate things.
Heaters basically consist of a heater core, or small radiator that water runs through, and a blower fan to distribute any heat that is present up through the vents. I say, “any heat that is present,” because if you never knew why heaters don’t work too well when the engine is cold, it is because the same antifreeze/coolant that helps keep your engine from overheating is used to keep the vehicle warm in the winter. This means when the engine is cold, so is the water in the heater core; and therefore no heat in the vehicle.
If you didn’t get the desired heat this year when you fired up the heater, there are a few things you can check to get some warmth in the car. First, check the level of the water in the radiator, preferably when the engine is cold to avoid burns. A low water level in the cooling system will keep the coolant from circulating properly so no warm water -- no heat.
Next, verify the engine is heating up properly. A laser thermometer aimed on the upper radiator hose or thermostat housing should show between 180 and 200 degrees as a normal temperature. A much lower temperature would indicate an open thermostat or low water/no circulation condition.
Depending on how the car was designed, it may have a heater control valve somewhere on a heater hose. These hoses are usually three quarters of an inch in diameter and run from the engine to the firewall on the passenger side. You can laser thermometer them or carefully feel both hoses to see if they are hot. One hot and one cold may indicate the valve is stuck closed, although it is normal for some variance in temperature between the two.
Usually, if both heater hoses are hot and you still don’t have heat, it could be a blend door sticking and not allowing heat to enter the vents. In most cases, when the vehicle is equipped with blend doors, there isn’t a heater control valve present and water circulates through the heater core year-round. The blend doors control heat, but it is always present. A heater control valve regulates heat by shutting the flow of water down to the core.
If the car hasn’t been maintained properly, it may have a clogged heater core. When the core clogs, water cannot circulate through and it can’t get hot. This can happen if too much radiator “stop leak” product has been added to the system, or the system hasn’t been properly flushed at normal intervals.
Send your vehicle maintenance questions to Jeff Deines. Email nkilbey-smith@wcn-online, putting “OTRA Question” in the subject line.
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