Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing 1996 +4 Heater Fuse Blowing?

Hi All,
I have a 1996 +4 and the heater fuse keeps blowing. I have put in a 30 amp fuse, it works for a period then it will blow at random. I have checked the wiring all looks ok.

The fan also only works on position 2 so no function on position 1.

Any ideas what the issue could be?

Switch faulty or sticky heater motor?

Many thanks
Will

Something is causing a big draw to blow the fuse. It souds like a faulty switch or motor. The switch is an easy check assuming the power goes via the switch to the fan. I would disconnect the fan side lead and then use a bulb or multi meter to see if it works in both positions.

The motor I'm guess if like my 97 +4 isn't easy to reach. Others may have more experience & some ideas

A word of caution though the switch may have failed due to the motor pulling a big current os replacing it alone may not fix it.

Possibly a contact in the switch coming adrift and shorting it out at odd times?

K

Sounds like the motor itself with an internal winding issue maybe. This could explain both the missing low speed and excessive current draw on high speed.

To prove you could gain access to motor and try dabbing direct +12 volts on green/slate and green/yellow wires to see if each speed works. I would be wary of leaving a 30 amp fuse in the main circuit though.

Many thanks will check the switch.. as for the motor anyone know if they were fitted to anything else other than Morgan’s…. The Morgan price is £420 for a new motor which seems rather pricy..

Also does anyone know where the switches are off, an Italian tractor comes to mind…

I'm sure Uncle Melvyn sells them but someone like Holden classic could be cheaper for switches.
You might find someone who can rewind the motor

Hi Will,

There is a generic issue here that has to be mentioned.

But first, at a glance, your symptoms indicate RichardV6 is right and is suggesting the right course. By windings, he speaks of a wound coil looking thingie that creates resistance and therefore reduces the effective current and therefore fan speed. Ergo, a two speed heater fan should have three positions. One that sends no current, a second position that sends a current through the windings (slow speed) and a third that goes directly to the fan. (I am ignore the possibility of relays.) I also like his action plan.

N.B There is no electrical diagram for Morgans made between 1990 and 1998. Nothing in the handbooks either. All other years from 1950 to 2019 are more or less covered. I have been trying to cob something up from trial and era with the help of moggers for 15 years. ANY information would be helpful/ But instead you could glance at my Morgan's earlier diagram https://www.gomog.com/allmorgan/wiring88&89.jpg speocifically the area found at the right middle. You will see my heater blower switch and blower with two paths between, indicated by RichardV6, with his wire colors.

The switch is simple. It could be shorted by melting from your present situation. Who is the supplier of your switches...VDO? Piccie?

Can you ascertain the supplier of the heater/fan unit. After they stop installing Smiths (the most reliable heater and still supplied today (parts or assembly) and taking, BY FAR, the least space. Do you have a piccie from under the dash and bulkhead? Fan motors are not difficult to replace and cheap, and aftermarket is even better than what was original. But let's finish diagnosis.

MORE IMPORTANT STUFF

The British gave many important things to the world. One of them was color coded wiring. Fuses are great. They are designed weakpoints. Rather than have one's car wiring melt when there is a short or wire failure, why not create a pre-designed wiring weak point, in a convenient place. It was called a fuse (odd name but a welcome idea) . Later, it was brilliantly realized that fuses of different strengths could be installed for each or a limited number of items and that would help with diagnosis or where the problem was WITHOUT the entire car closing down. Fuseboxes became bigger and bigger. By 1987 every mogger could be a diagnostician! Sadly, that has recently ended with the advent of more-profit making PCBs or such, a big prejudice to automobile repair.

Yes, we all try a one size larger fuse when a fuse fails. But more than that is unwise. Fuses don't fail for no reason. If we make our fuses so strong they cannot do their first job of protecting the wiring..that is very unwise.
The worst example I have ever seen, was at the start of the European GEMS era. Those cars put out a lot of heat. The radiator fans were inadequate. So they put in SPAL fans which drew enormously more current. To compensate for the increase in draw, they installed a 40 amp fuse in the old slot in the fusebox. The fuse slot and fusebox were not rated that high..neither was the car wiring in general. The wiring, sometimes the fuse box slot,etc burned, the fan failed and new car engines blew their head gaskets in traffic.

If you are up to 30 amp fuses and they are failing, stop now. Sort this thing first.

gmg

P.S. If the motor is shot, they are cheaper to buy new than repair.

Many thanks all.

I suspect it might be the motor playing up given the symptoms, the output now when on is quite weak..

Pics below:





Any suggestions for a replacement motor?

Many thanks
Will

It looks like a lot of corrosion on the wiring. It might be worth a quick spray with connector cleaner before surgery.

The MMC had many supply issues after they ended the Smith's cabin heater system (which are still available in either new whole systems or parts). According to the old parts books (with overlapping transition), the MMC fit one type from 1984 to 1987, then another 1987-1993, another 1993 to 1997, another type 1996-1997 and then another from 1998-2000. After that the systems (used also for AC) became the subject of many woeful discussions here and everywhere. Moggers of post-2000 cars are beginning to remove these last systems, likely at the suggestion of predatory or poorly trained experts, (a sign over the door does not an expert make!) The latest systems might be poorly designed but THEY are curable at little cost. A properly trained and honest Aircon/heating person knows so. It is fascinating watching who does what. Removing entire heating system is very invasive and costly. Changing the pumping and components is cheap.

There is sadly no mention in these parts books of the supply system after the Smiths but I believe you may had a Galley heater. But that is no help as I am also told Galley do not answer request for parts.

All that being said, do not dismay. It is only the general design structure that can vary. The component parts of cabin climate systems is are largely generic and very cheap unless you buy them from the auto manufacturers that use them and supplied them for your car. You can easily find a buffet of fan motor replacement. At worst that will require an adapter plate you can fashion yourself with a drill and a bit of metal plate. For example, I have never had a problem with my trusty Smiths (though I have had two other MMC climate systems). However, I wanted more airflow. So I merely bought a stronger fan motor (25£) swapped it in and added a 4 identical position switch (off, speeds 1, 2, 3) (I use sturdy little metal toggle switches).

HOWEVER, all this is premature unless you want to save time. You may merely have a wiring problem, not unusual in a 28 year old system exposed to the elements. Once found, you can costlessly set it up so it will NEVER never occur again. If you want to upgrade performance, you can take the other route I am suggesting. I always think of such issues as the car's signal to me that it wants to be better. Amazing what that can produce over time.

As for a specific suggestion, work by dimensions with an eye on cfm. I will help if you publish the dimensions

gmg