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MG MGB Technical - Uneven heat from heater

Hi All,

My heater works fine on three of the outlets (both footwells and the passenger screen), but is poor on the right hand side of the car. The air flow is fine, just very low heat in comparison to the other outlets. Do you think this could be due to a partially blocked matrix?
All the air hoses are connected ok from what I can feel.

Thanks,
Matt
MattWilkinson

Unlikely I would have said, the hot air to all four places comes from the same place. If it was being caused by a partially blocked matrix, and the outlets ports effectively took their air from different parts of the matrix, then it would affect air flow to the outlet that was experiencing the blockage. Any other blockage, like around the flap that controla air direction, or misplaced or blocked tubes to the drivers demister, would result in low flow, but as hot as the others.

It could be that the foam seal round the matrix has perished in one place, so air is bypassing the matrix altogether at one point, and the majority of that unheated air is going to the drivers demister.

It's one of the worst jobs on the MGB to remove and dismantle the heater (although not as bad as on many modern cars where the whole of the dash has to come out and is a much bigger job). I believe it is possible with a bit of violence to remove the cover from the heater with it still in-situ in the engine bay, and you may be able to inspect and replace the foam.
Paul Hunt

Matt,

sometimes the isolating foam of the heat exchanger deteorates and is blown into the hoses that are directed to the defroster jets where it will block most of the hot air currant.
Looks like you have to take the plastic hose off and check it for jam.

If you want to take out the heater box itself, NEVER take off the adjusting cables at the box but at the regulator knops.

You can also fit a aditional relay to the heater motor that is operated by the heater switch. If the working contacts of the relay are connected to the fuse box by short and thick wires (purple circuit), the blower motor will run much faster on most B's and it might blow out the jam this way.

Ralph
Ralph

Ralph,
That's an interesting point you make about leaving the heater cables attached to the heater end when you take it out. Do you recommend attaching them to the heater before reinstallation? My reinstallation is some way off but I'd welcome any advice to make the job easier.
Regards
Richard
Richard Coombs

My guess is that the heater trunking for the right hand defrost has come off the box (behind the centre console). Mine just did!
It's fiddly but it can be pushed back on (at least mine could)
Neil McGurk

Richard,
Yes, fit the cable to the flap at the base of the heater before you fit it to the car. Check that the thick rubber seal fits to the heater without being pushed out of place by the cable or any screw heads. Mine needed cutting to get a snug fit. Feed the cable carefully through the hole and into the car as you feed the heater into place. Some lubrication may help. Check progress from inside the car as well. The hole the cable goes through can be opened up to make a slot to help. Althouigh it feels impossible at some points, they do go in with some gentle persuasion.
See these links for mode detail
http://www.mgb-stuff.org.uk/heaterframe.htm
http://www.chicagolandmgclub.com/photos/b_heater/
Have fun
David
D Balkwill

You have HEAT!?
Pete

As I said before I doubt it is the trunking blocked or detached as Matt reports he is getting *cold* air, not *no* air.
Paul Hunt

This thread was discussed between 22/10/2008 and 23/10/2008

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