Heater Box Mounting Mod

[BryGuy]

Anyone who's removed the heater box knows it's a PITA

 

The Culprit:

 

Missing from the picture is the nut that threads onto the long finer threaded side. In theory to remove the heater box it should be as easy as removing the 5 nuts and pulling the heater box out from the inside. The problem starts when the nut rusts on threads. Typically a rusted nut isn't a big deal.... apply some penetrating lubricant and/or some heat, apply a bit of torque and the nut usually breaks free. The only problem is that almost any torque applied to the nut causes the thicker threads on the opposite side to rotate, due to the fact that they are threaded into plastic. That's typically when the cursing starts and the minor problem of a rusted nut becomes a nightmare.

 

I've removed 3 heater boxes and all 3 gave me the same problem.

 

Even after you manage to remove the heater box, your now left with another problem.... the mounting holes in the plastic are now sloppy due to the fastener spinning around.

 

My Solution:

Junk the old mounting hardware and replace it with Stainless Steel grade 8 coated bolts, nuts and washers.

 

Tools Needed:

- Drill with 13/64 bit

- 13/64 Drill bit

- 2 9/16 sockets with ratchet

- 1 9/16 wrench (preferably a ratcheting one)

 

Materials Needed:

Qty 2 3/8 -16 x 2-1/2" Zinc Plated Grade 8 Bolts

Qty 2 3/8 -16 x 1-1/2" Zinc Plated Grade 8 Bolts*

Qty 1 3/8 -16 x 2" Zinc Plated Grade 8 Bolts *

Qty 10 3/8 Zinc Plated Washers

Qty 5 3/8 Zinc Plated Nuts

* I lost my notes, so the length of these might be wrong. I will double check soon.

 

Step 1: (Assuming the heater box is already removed from the vehicle) Remove the panel that allows you to gain access to the heater core. 10 fasteners hold this cover on (see red circles on Pic #1 & 2), 8 on the top, and 2 on the back. Once these 10 fasteners are removed you will need to release 3 clips (see yellow boxes on Pic #2). With the fasteners off and the clips released the panel comes off easily. With this cover off it will allow you to get your hands on the inside of the heater box for step #3.

 

Step 2: Using a 13/64 drill bit drill out all 5 of the mounting areas so that there is a hole all the way through the heater box to the inside (be careful not to hit the heater core with the drill bit). The holes are purposely drilled smaller than the diameter of the 3/8" bolts, and is explained in the next step.

 

Step 3: Place a washer on a 2-1/2" bolt. Starting with one of the mounting holes closest to the heater core, thread the bolt in by hand for the first couple of threads and then all the way through with a 9/16 socket and ratchet. Snug it up so the washer just starts to dig into the plastic. Repeat this step for the second mounting hole above or below the one you just completed and continue to Step #4.

 

Step 4: Follow Step #3 on the middle mounting holes with the following differences - 1-1/2" Bolt, using a 9/16 wrench due to limited space.

 

Step 5: Follow Step #4 on the remaining mounting hole with the following difference - 2" bolt.

 

Step 6: Reattach the panel removed in Step #1.

 

Step 7: Reinstall the heater box using the remaining 3/8" washers and bolts.

 

Pic #1

 

Pic #2

 

Pic #3

 

The Conclusion:

The jury is still out. Since I'm still in the design phase of my project I've had my heater box removed and reinstalled a few times now with no troubles..... BUT there isn't any rust or corrosion on the nut, so very little torque is needed to remove the nut. In theory I could run into the same problem with this set-up as occurred in the previous set-up. I do believe this modification will fare better for the following reasons:

 

1. The hardware is zinc coated and far less likely to corrode/rust.

2. The threaded area in the plastic is a greater length thus providing more resistance and making it less likely to strip.

3. Even if the same problem occurs the bolts can be cut off and replaced.

[Alexia]

Same problem here with all the HVAC units I removed. I just put the studs back in after having carefully removed them in the first place. I never had a problem with the holes widening.

[dasbulliwagen]

Mine did this as well, I think I used a little two part epoxy on the plastic side before screwing them back in to keep them in place. No problems, and less work.