Installing a fan relay only helps when stationary, and then only a little,
and may only be compensating for poor connections in various places. Many
problems in the heater system such as blocked matrix (coolant and air),
poorly adjusted valve, a non-OE valve, poorly adjusted air flap, unglued
felt strips on the air flap can contribute to poor heater output. Having
the fan motor connected round the wrong way makes a huge difference (on all
but the earliest cars), try it both ways and see. A properly set-up heater
system should burn your feet, as the Navigator complained of just yesterday
when it was bit cool on the way home from a run. With a standard system
including unmodified OE water valve I get very similar outputs to Bob Munch
after his modifications - 150F - and that was with an ambient of around 50F.
You may want to check how effective a relay might or might not be by running
the fan as normal and taking a jumper lead from the brown at the fusebox to
the green/yellow i.e. in parallel with the existing wire, ditto with a
ground. If you still want to fit a relay mount it by the fan (no need to do
anything behind the dash, only by the heater motor), take the green/yellow
that presently feeds the fan and take it to one side of the relay winding.
Take the ground that feeds the fan and take that to the other side of the
relay winding. Take a heavy gauge brown, via an in-line fuse, from the
fusebox and connect it to one side of the relay contact. Take a heavy gauge
wire of another colour from the other side of the relay contact to the
green/yellow of the fan. Finally provide a heavy gauge black from the fan
black to a good local ground point on the body. For late cars with a
2-speed fan you only need one relay for the 'normal' wire and not the 'slow'
wire, obviously.
----- Original Message -----
From: "MonteMorris" <mmorris@nemr.net>
To: "MG list" <mgs@autox.team.net>
Sent: Monday, September 01, 2003 10:33 PM
Subject: heater rewiring
> Sometime in the last year someone posted a fix for poor heater output by
> rewiring it with heavier wire and (I believe) installing a relay. I've
> searched the archives and lister's websites but can't find it.
> Could someone point me in the right direction?
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
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