Heater mystery...

[robedney]

Mildred is a 1967 two door that I've recently been lucky enough to acquire and her heater is something of a mystery to me (in two ways). Forgive me for questions like this, but I'm handicapped by living in a place where there's not another moggy just down the road to sneak a peak at.

First, she came with no heater fan. The odd thing is that one side of the heater box is blanked off with a steel plate spot welded in -- very factory looking -- while the other side has the 3" white plastic tube extending out, to which a shaggy piece of duct hose was connected. I've managed to get a look at a couple of heaters on EBay, and I can see the fan motor sticking out on the side that -- on my heater -- is blanked-off. Now, I would tend to think that mine never had a fan if it weren't for the presence of a fan switch and power running to it from the harness. That's the mystery. I've resolved this by using a new 4" bilge blower fan (made for venting bilges on boats with gasoline engines to avoid mayhem) and I'm wiring it in with a ballast resistor/SPDT switch so as to have 2 speeds. The fan fits nicely inside the box and moves quite a lot of air. Nonetheless, I'd love to know what the original was.

Secondly, it appears that the original moggies had a heater with no fresh air input, while the later versions (like mine) had only fresh air input (from the input hose that runs from the heater, through the engine compartment to a port in the front grill). Ideally, one would be able to adjust the mix of fresh/recirculated air depending upon the need. Was there any provision for this? If there was, mine is missing it. I'm considering building a little flap/diversion box to achieve this mix, and putting it inline between the heater and the firewall. It's wonderful to be able to quickly ventilate a car with fresh air -- particularly when it's been locked up sitting in the sun. It's even better to be able to increase the efficiency of the heater by recirculating part of the already warmed air from the interior.

[simmitc]

The standard car would definitely have had a fan fitted. The only thing I wonder is whether there was an export spec that omitted the fan? Unlikely, but plausible - some cold climates had a fan at the front of the car, at the start of the air intake hose. Of course, thinking about it, that would mean no fan in the heater unit....

There early cars had a semi-recirculating heater, but the later cars had no option to change the mix of fresh air, it's just fresh full stop. Some people move the air intake behind the radiator so that pre-warmed air is drawn in, but a mixing box sounds like a good idea.

[bmcecosse]

Very strange - I think some early Mini heaters had the fan motor at the rear of the box - maybe someone fitted a Mini heater? Have you had the complete box out on the bench - definitely no fan to be found ??? And no - there never was any way to select fresh air or recirculation air, or to mix them ! Owners were just glad to get a heater!

[liammonty]

At the risk of sounding like a Morris Minor heater 'anorak' (no pun intended) you could select 'external' or recirculate on the last type of the round heaters that were fitted, up until '63 ish- there's a control that looks like a choke knob on the parcel shelf that opens up a plate and allows air in from the box section near the steering rack (I think!). You don't get much in the way of ram effect from it (not like the tornado you get on the later cars, that's for sure), but you can switch between recirculated and 'fresh'. Earlier cars were only recirculatory though.

[deano69]

there's a control that looks like a choke knob on the parcel shelf that opens up a plate and allows air in -

'Pull' to open-allow fresh air in- and 'Push' to close-stop fresh air entering ?
Ive got a round heater in a 1963 minor and it seems to do as it wants with regard to heat or lack of.I've turned the tap to fully open at the rear of the engine and twisted the front of heater switch to what i thought was hot setting but it seems to produce less heat now than it did 3 weeks ago.

[MarkyB]

Try turning it back a little bit, I think the fan goes off again when the knob is fully turned.

[liammonty]

For the older style round heater- Yes- pull the knob on the parcel shelf out for fresh air (helps stop the windows misting up quite so badly). The knob on the front of the heater doesn't affect heat per se, but it's a rheostat that alters the speed of the fan. For full speed, turn it just slightly clockwise from the 'off' position- the further you turn it clockwise, the slower the fan runs (like MarkyB said), though it doesn't turn off totally. You'll want it running flat out in this weather! You should get a reasonable amount of heat out of it set like this- they're not great, but do the job. The main problem in my '62 saloon is keeping the cold air out- door and window seals are horrendous...

[robedney]

Ah! "simmitc" may have gotten it! I'm not near the car at the moment (they insist on my coming into the office if I want to get paid) but I remember a mystery mount of some sort in the engine compartment more or less along the path of the fresh air intake hose for the heater. That would have been an obvious spot to mount an external fan under the hood -- and would explain the configuration on my heater. I'll be able to confirm that by the wiring, of course. If so, I'm glad I've done the modification I have (putting a fan in the heater box) because I'll definitely build a switching box to allow mixing both fresh and recirculated air -- and an under the hood fan would have made that impossible (well, I can think of a way using a venturi fitting of some sort, but it wouldn't have been as efficient) You can see my bilge blower heater tucked inside the heater box here:

The standard car would definitely have had a fan fitted. The only thing I wonder is whether there was an export spec that omitted the fan? Unlikely, but plausible - some cold climates had a fan at the front of the car, at the start of the air intake hose. Of course, thinking about it, that would mean no fan in the heater unit....