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Troubleshooting Guides - Sorting A Heater

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Troubleshooting Guides - Sorting A Heater

Postby TechTeamMod » Sun 7th Sep 2008, 07:01pm

Making a heater work
It's a common problem on minis - You get in your car to go to work on a cold morning and it takes so long for your windscreen to demist that you end up wiping it with your sleeve. Then, you sit in the rush hour traffic, shivering all the way to work. Luckily, it only takes about an hour to solve the problem, and usually without costing more than a couple of quid's worth of antifreeze.

Heater Valve
If the heater does not blow hot or at least warm air, the valve in the engine bay may be stuck and won't open. The same applies if the valve is stuck on hot and can't be closed. The location of this valve varies on the year and model of the car, but is either on the cylinder head adjacent to No. 4 cylinder or in-line in a hose from the opposite end.

To check the valve:
Run the engine until it's warm and open the heater valve. The hose from the engine to the heater should become warm, if not it may be seized closed.

If it can't be suitably freed with penetrating oil it is easy and cheap to replace.

Cleaning the Matrix
Firstly grab a bottle of cooling system cleaner and add it as per the instructions on the label.
Remove the heater unit itself from the car:
Drain the coolant (by removing the radiator bottom hose) or use hose clamps to isolate it from the rest of the cooling system.

Place a container under the heater as you remove the hoses, as it'll still contain coolant and is bound to slosh over your carpets.

Disconnect the contacts from the fan switch.

Undo the two screws underneath the switch panel at the front of the unit, and loosen the nut(s) on the retaining bolt on the rear.

Connect a garden hose to one of the unions and flush the matrix through with water until it runs clear. Connect the hose to the other union and flush again.

Fan and switch
Use a multi meter to test the operation of the fan switch.
Set the meter to measure resistance, flick the switch to the ON position and touch the test leads on each of the switch terminals. If the reading on the meter does not head for zero when you do this, the switch needs replacing.

Refit the heater unit, connect the leads back to the switch and turn on the ignition and heater. The fan should immediately start, and blow air through forcefully. If this doesn't happen the fan motor is probably faulty and should be replaced, although this is not a common problem.

Air feed
Remove the air ducting (leads from the grille to the heater) from the car and ensure it's not blocked with general crud like leaves. If the ducting is damaged, it can be replaced with better items from a scrap yard.

As above, check the ducting from the heater to the windscreen vents for any damage and blockages. Again, if they are goosed, grab some better ones from a scrapper. On refitting, the ducts can be taped into place at the ends to ensure all the air is sent where it's wanted.

Check the operation of the lever that directs the air either the car or the windscreen. These tend to wear, and do not properly aim air to the windscreen. They can be replaced cheaply with brand new ones that will work properly and not rattle.

All Done?
Reconnect the hoses to the heater and top up/refill the system with water and antifreeze as required. Start the engine and allow it to get warm, open the heater valve and keep topping up the coolant all the while to ensure all air bubbles are removed from the system.

Once the engine is up to temperature, and with the heater valve open, turn on the fan. Warm air should flow from the heater, and from the screen vents when the lever is slid to that position. Close the heater valve and the flow of air should cool although, minis being minis, will probably not blow cold!

A sticky thermostat could also be part of the problem. Also, if you've taken the bottom hose off the radiator, this is the ideal time to flush the rest of the cooling system.
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