View Full Version : FJ40 heater/fan operation

08-30-2009, 03:12 PM
Question - On FJ40s the first pull of the heater fan knob is supposed to be low fan speed, front fan only. The second pull is supposed to be high fan speed, both front and rear fans. That is great if/when you want heat, but what if you want cool air? Can only the first pull be used if you want the vent, because otherwise the rear heater will be turned on, which isn't exactly what you want on a 90+ degree day...

08-30-2009, 03:44 PM
I'm not sure on the later 40's, but on my '73 there are separate front and rear fan controls and a separate "fresh air" control that opens the cowl vent. There is no temperature control, so basically, any time you turn the fans on, they are going to pull air past the heater cores and blow heat. There is no way to have the fans blow fresh, unheated air. I've seen people connect a valve to the heating lines at the firewall to selectively block the coolant from reaching the cores.

Just take your top and doors off dude. ;)

08-30-2009, 05:20 PM
In theory you should be able to get unheated air with the Fan switch pulled one step as long as the Warm Pull is depressed, so that hot water isn't circulating the heater core when air is blowing through. But I think in reality there's always some amount of warm water in the core, and so it's almost always blowing heat.

I haven't quite figured out what the Fresh pull actually does. It's not a cowl vent like in the earlier models, but instead it's supposed to open a door in the fire wall to allow fresh air into the system. I'm not sure mine's working though...

08-30-2009, 05:52 PM
The fresh pull door DOES work on mine. And I think in theory the valve (not sure if it's stock on your Martin, but it is supposed to be on mine - I have one but it's corroded so it doesn't work that well, so I just pulled it off for now) that blocks coolant is supposed to do a pretty dang good job of it. And that answers my question. With the Warm Pull knob depressed you should be able to run both fans (and the front one on high) and not have any appreciable heat coming off of them. Thanks Martin and Matt!

08-30-2009, 06:20 PM
I tested my valve last week (since I've got the radiator and heater out of the truck) and it seems to be working well. But I never could get warm air from mine since I've owned it, so I'm hoping that flushing the system, boiling out the cores and restoring the unit will get me some warmth.

08-30-2009, 09:52 PM
But I never could get warm air from mine since I've owned it, so I'm hoping that flushing the system, boiling out the cores and restoring the unit will get me some warmth.

Cleaning things up is a good step. I was getting heat out of my heaters on an intermittent basis until I discovered that there was not thermostat in my truck. The heater will warm up the truck very nicely when everything is working.

Matt, your heater allows you to open and close the valve from inside the cab. In my truck I have to open and close the valve under the hood.

Regarding getting cool outside air to flow with the aid of the fan, it is not really possible because even with the valve off the heat of the firewall is enough that it is always warm.

08-31-2009, 07:35 AM
I actually have a "Warm Pull" knob to the far right on my dash that operates the valve. The heater controls flip a gate inside the heater box that either forces air over the heater core and makes it come out near the bottom, or diverts it back up through the vents at the top.

It IS only a vent, so on hot days it will blow air that is the same temp. or even a little warmer than outside air (because of the heat from the engine and any heat transferred through the heater box).

Anyway I was just curious on the philosophy of how this was supposed to work, and forgot that there is the valve that cuts off the coolant flow to the heater cores.