Heater Motor Replacement and Maintenance

Heater Motor

Original equipment Jeep® heaters are sometimes called “placebo heaters” since any heat you feel is only in your mind.  You hear the fan running but only a wisp of hot air comes out.  Below are a couple of procedures that might help.  One is how to open up and maintain an original heater motor.  However, even at its best it’s pretty lame.  OK, at its best it’s completely lame.  Take a look at how to replace the motor with one from a mid to late ’70s Chevy.  And click here to see how to add relays to the system to take the load off the original wiring and switch.

Heater Motor Information and Identification

I’ve seen a number of web pages dealing with how to switch the anemic Jeep heater fan motor with a much better one from a mid to late 70s Chevy truck.

Old heater motor

From my research on this it appears that older CJs up to about 1970 or so can be modified.  Heaters in the older Jeeps will be on the driver’s side of the Jeep.  The fan motor faces the driver and is near the driver’s left knee.   The procedure outlined below should apply to this early era of Jeep CJ.

Jeeps from 1971 to mid-1977 would be very difficult to upgrade.   Heaters in these years will be on the passenger side of the Jeep, and the heater motor will be inside facing the passenger.  Due to the way they did the fan motor mounting plate, upgrading one from this era would involve a lot of fabrication.

CJs from late 1977 on up should be a relatively easy bolt-in, although you’ll have to drain the cooling system just to get the whole thing out.   The heater will be on the passenger side of the Jeep, but the fan motor housing will be sticking through the firewall.  See any one of the many sites on the web for details on how to do this style of replacement motor.  This last group is the one all the web pages I found deal with.

Up to 1970Fan motor faces the driver and is near the driver’s left knee.The procedure outlined below should apply to this early era of Jeep CJ.See procedure below.
1971 to mid-1977Fan motor on passenger side of the Jeep facing the passenger.Difficult to upgrade.ue to the way they did the fan motor mounting plate, upgrading one from this era would involve a lot of fabrication.
1977 onFan motor on passenger side of the Jeep with motor housing sticking through the firewall.Relatively easy bolt-in.Drain the cooling system to get the whole thing out.  See other web sites for procedure.

Procedure for older CJs

First thing is this all assumes you have an existing heater system in your Jeep and that it’s the one located left of the drivers side under the dash.  You will not need to drain the cooling system to remove the motor.   You’ll need the old fan and a few other parts from that old system.  Get a suitable motor; I recommend getting a new one.  It makes no sense to go to this much work just to put in an old motor that may or may not last.  When you get to the auto parts store, ask them for a heater motor for a ’73 Chevy Blazer with a 350 and air conditioning.  This will run about $20 or so.  Pick up some 20A fuses while you’re there.  Mine were the SFE style (about 5/8″ long).  Check yours before you go and get the style and size you need.

Now, before doing anything else, mark the old mounting plate and heater housing for correct orientation (I like to use bits of masking tape).  This will greatly simplify re-installing the new motor.  Transfer this locator mark to the new motor plate and the spacer you’ll make a little later.

Next, pull the old motor.  On the older Jeeps this is a much simpler job than later models since there is no firewall hole to enlarge and you don’t need to drain the cooling system.  Unplug the hi and low wires from the switch, and unscrew the 5 screws holding it in place and it’s out.

In my case, in order to use the original fan I had to make a spacer to go between the new motor mounting plate and the heater housing.  I made one out of 3/4″ thick wood (particle board).  Use the old plate for a guide since you can disassemble it from the old motor and lay it flat on the wood.  Mark all the mounting holes, then just freehand a circle that stays about 1/4″ outside all the holes.  Draw another circle that stays about 1/4″ away from the mounting holes but on the inside.  Cut out the spacer.

Now here’s the interesting part, and this is what fooled me when I first did this.  The old motor and the new motor have different rotation directions.   When you spin a squirrel cage this turns out to be a big problem.   The squirrel cage fin pattern and the heater housing design must match up with the rotational direction of the motor or you won’t get any more airflow than you had before, and you might get even less.  So, you’re going to have to reverse the new motor’s rotational direction.  Now stop whimpering and whining, it’s pretty easy.

Drill out or grind off the 4 rivets holding the mounting plate to the motor.   You can then lift the top end of the motor off the motor body.  Be careful as there will be 2 brushes, 2 brush springs and a shaft washer that will want to jump out.  It’s OK to let them jump out, just don’t lose them.

To reverse the motor, all you have to do is swap the position of the brush assembly that is grounded with the brush assembly that is “hot.”  (Note: thanks to Roy Jenson for help on how to do this.  It’s still magic to me that swapping the brushes reverses the rotation.)  After that, reassemble everything.  It takes a little dexterity to get the brushes back into place but it’s not too bad.  I recommend you use a pop rivet gun and pop rivet everything back together.

Next, you will note that in addition to the mounting holes on the new mounting plate that there are a number of “extra” holes that normally you wouldn’t use.  However, I found that it was much easier to use these extra holes to screw the spacer to the plate so it doesn’t flop around when you try to install it later.   Use the old short sheet metal screws from the old motor for this.

Drill the mounting holes through the wood spacer.  Get some longer sheet metal screws (they have to go through the plate and the spacer now) and mount the new unit.

Put in your 20A fuse.  You will have to make up a new power wire harness.  I made one that allows a low and hi fan speed.  For the low speed you will need dropping resistors.  I’m using two 2-ohm 25W wire-wound resistors wired together in parallel giving me a 1-ohm total resistance which provides a good low speed.  You can get these resistors from Radio Shack® online, a local electronics store, or go to a junk yard and get the heater resistors  there.  Wire the low speed terminal of the switch to the resistor(s), and the resistor(s) to the power terminal of the new motor.  Wire the hi speed switch terminal straight to the same power terminal on the new motor.  Radio Shack® sells some neat little spade lug adapters that will make it easier to attach the 2 different wires to the motor’s single power terminal.

New heater motor

That’s it.  You will now have a real blower in your heater system and you might even get some air out of the defrosters (if you have the defroster windshield option).