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MG MGB Technical - heater

the heater in my 74 does not work. Is there any way of telling if it is the blower motor or on/off switch?

rick baranyi

The simple way to test the fan motor is to disconnect the two wires at the motor and connect them to 12v and ground.
Dave O'Neill 2

And to tell if the heater is working, the rubber hoses to and from will get hot once the heater control is on.
Michael Beswick

Even if the motor isn't running the heater should be outputting a significant (for an MGB ...) amount of heat when driving along. The only time I've ever used the fan is when travelling slowly in cold wet weather to keep the screen clear.

I have determined that the fan switch is bad.
How do you reach it and replace it

rick baranyi

I'm glad someone gets heat from their B. At best, mine is a warmer. The heat control works but not much heat comes out


79 MGB
gary hansen

Half, at least, of the problem with B heaters stems from the valve. It's prone to internal corrosion severely diminishing it's ability to pass water. I've binned them and use RV8 style valves. Very simple rotary valves.
Allan Reeling

I've measured the output of mine at 60C/140F on a 8C/46F day. It has been known to burn our feet and the Navigator request that it is turned down.

There can be no less than ten places that can contribute to poor output. But at the end of the day Roger Parker has observed that some cars are just better than others, when as far as it can be determined they have an identical installation. One additional possibility is crud and reduction in flow in the block itself.

From what I can see in the WSM American padded-dash switches seem to need one of two U-shaped tools to compress the tabs on either the bezel which then comes forward with the switch, or on the side of the switch so it comes out on its own.

This thread was discussed between 20/10/2016 and 29/10/2016

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