The Hot Switch (Coolant Vacuum Valve Switch)

Understanding Your Coolant Vacuum Switch

When the weather gets cooler, you want the cabin of your vehicle to stay warm.  When you switch on the heat, you may find the air that comes out of the vents just isn’t hot.

The problem could be a part of the heating system that not that many people understand.  It’s called the coolant vacuum valve switch or thermostat vacuum switch.  Here’s what it does.

How to Replace a Coolant Vacuum Valve Switch | YourMechanic Advice- All Pro Servicenter

When you don’t need heat in your vehicle, you don’t need hot coolant from your radiator to go through the heater core in your vehicle.  (The heater core is like a small radiator that exchanges heat between the coolant and your cabin air.)  When you turn on the switch for heat or defrost, it signals the coolant vacuum valve switch to open.  That should send hot coolant to the heater core which heats your cabin air or defroster air.  If the coolant vacuum valve switch isn’t working, you don’t get warm air to either.

What are other causes of coolant vacuum switch failure?

Sometimes the coolant vacuum valve switch can crack, be jammed up with dirt or debris, or even be clogged up with old coolant.  Another sign your coolant vacuum valve switch isn’t working is engine overheating. If it’s cracked, you may see coolant leaking under the dash or smell an odd, sweet odor.

What to do if your coolant vacuum switch fails

If you notice any of these symptoms, you should have your vehicle checked out at your NAPA AutoCare Center.  Other things can cause your heat to stop working – your qualified technician will be able to diagnose the problem.  Make sure you and your passengers stay warm, and your windshield is properly defrosted.

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