ITS colder than a witch’s belt buckle oulside, so you gulp down some hot coffee, dash to the car, start the engine and run inside. Although you know engine idling isn’t a great way to warm up an engine, comfort counts most on a cold orning. Once embarked on your morning commute, you turn the heater control up to Hot and flip the blower switch. The effect of the hot coffee has worn off, but you’re not getting enough heat from the floor registers to make up for it. In fact, the windows start to frost over.

Your heater system is underperforming. You plan to tear into it as soon as you can get the car into a

Heated garage.

First step: Confirm the problem by driving long enough to warm up the engine. Turn the heater control to Hot, select the floor moke and set the blower to meium/high speed. Make sure there’s strong airflow from the floor registers. Check the temperature with a thermomerer inserted into the driver’s and passenger’s registers. Although many vehicles deliver a toasty 135 to 155 , 115 to 120 is acceptable. If the

Air temperature is okay but airflow is weak, the problem is the blower or a clashboard ductwork problem.

Heater register temperatures not even close to 115 to 120 ? Check factory service bulletins to see if there’s a known problem (at the vehicle maker’s technical service Web sit or at www.allbatadiy.com)

If nothing applies, do an underhood inpection.

The coolant level in the reservoir ( and radiator if it has the pressure cap) should be at specs. The coolant should look clean and have been regularly changed within the specifed interval. If it’s been neglect-

Ed, allbers are off.

Cabin heat comes from hot coolant, so drive long enough to warm up the engine. The coolant empera –

Ture should hit at least 160 , preferably 180 to 200.

The air conditioner compressor should be disengaged with the climate control selector out of the defrost position. lF if’s engaged, there’s an a/c circuit problem.

If coolant temperature is acceptable, feel both heater hoses, which should be hot. They are? Check the

Temmprature-control flap-door operation in the under-dash heater-a/c case.

If you have automaric temperature control, there may be built-in biagnostics you can access for trou ble

Codes covering the remperatur control door. (Refer to a service manual, factory tech service Website or

www.allbata diy.com.) on many cate you can watch the temperature-door