Author Topic: Heater Blows Cold  (Read 1901 times)

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Offline mnevis

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Heater Blows Cold
« on: November 14, 2019, 12:36:54 AM »
The heater has started to blow cold when set to hot.   It blows cold regardless of temperature setting. The aircon is not being used but makes no difference if it is switched on.   2005 Maxda 3 RHD 1.6L petrol, Sakata  UK spec.  Below the bonnet I have noticed water on the plastic tray below the engine.  The water is mainly gathered on the side of the engine immediately below the cam belt.  The radiator hoses do not appear to be wet or leaking.  The radiator does not appear to be wet or leaking.  Any ideas anyone?   Also aftermarket parts.  Are they a waste of money?   

Offline StevenRB45

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Re: Heater Blows Cold
« Reply #1 on: November 14, 2019, 10:43:36 AM »
Is the engine over heating? If I recall the water pump lives on the left hand side of the engine but coolant would be disappearing if it was leaking. But given current weather may be a red herring.

There is a device called a blend door in the HVAC system itself which can fail and leave you with nothing.

Offline mnevis

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Re: Heater Blows Cold
« Reply #2 on: November 14, 2019, 12:12:11 PM »
The engine is starting to overheat.   Can you explalin more about the HVAC system

Offline StevenRB45

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Re: Heater Blows Cold
« Reply #3 on: November 14, 2019, 01:15:47 PM »
Given you've got overheating the lack of hot air is unlikely to be a fault with the heating system itself.

Has the coolant level dropped below minimum? If the water pump or cooling system has sprung a leak then it's probably low and no hot air may be due to their not being enough coolant circulating to warm the heater core.
« Last Edit: November 14, 2019, 01:21:39 PM by StevenRB45 »

Offline mnevis

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  • Engine: 1.6L
  • Fuel: Petrol
  • Model: Mazda 3
  • Transmission: Manual
  • Trim: Sakata
  • Year: 2005
Re: Heater Blows Cold
« Reply #4 on: November 15, 2019, 12:27:51 PM »
Hello everybody and thanks for the help.   The coolant was very low.  I put 2 litres of water in to bring it up to level and then the hearter was working.   Looking around the engine no water leak is visible.  It is not raining where I am and the roads are not flooded or wet.  There is an amount of water deposited on the engine bottom plastic tray in the area below the cam belt.   Unable to ascertain where the leak is or what is leaking.    I am monitoring the situation.  Thank you.

Offline StevenRB45

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Re: Heater Blows Cold
« Reply #5 on: November 15, 2019, 04:00:00 PM »
Be careful running water with current temperatures if it freezes you'll have bigger problems.

I'd suspect a leak either near or from the water pump.

Mazda 3 Forums UK

Re: Heater Blows Cold
« Reply #5 on: November 15, 2019, 04:00:00 PM »