Today I removed the module from the firewall, pretty simple to do. I saw no visible damage to the heater core so I capped the fittings and did an air test in a 5 gallon bucket of water.
Tiny bubbles, so a pin hole leak.
The inside of the module was FILTHY. The blower motor housing was full of leaves & debris and the evaporator was very dirty too.
There is no screen on the fresh air inlet to the blower motor to keep out debris, or the one on the firewall is missing/damaged, I will check it out.
The blower motor is an aftermarket model and the bearing is noisy/worn. This and the nest of debris I found explain that blower motor noise. I will get an OEM blower motor.
I labelled all the actuator motors and removed them. I washed the module and the evaporator and I will wash all the duct work also before reassembling.

Time to order some parts, I will begin re-assembly next weekend.

 

Restoration in progress:

I modified the module to accept a cabin air filter, and fabbed an access panel to replace the filter.
The module was re-assembled with new actuators, new heater core and re-installed to the firewall. I also replaced the heater hoses, quick connect fittings, and radiator hoses. (lower hose not arrived yet)
I should have the rest of the dash-re-installed tomorrow except for the part I want to restore, but I will have to wait for the lower radiator hose to arrive before I can top-off the cooling system.

I am going to toss out the Onstar system and make a cubby with a USB port for the cell phone, etc.

I also found the source of all the leaves and debris that was inside the module: There is a hole in the firewall (a OEM hole not a rust hole) behind the washer fluid tank, facing towards the fender I am going to get some screen material and rivet it over the hole. that will keep the blower from sucking leaves in under the hood. The cabin air filter will also keep debris contained within the blower motor chamber which is easy to service when needed.

 

If you're replacing the blower motor you may also want to replace the resistor. Mine was faulty and kept causing a parasitic battery drain. But that's easily accessible without removing the entire dash.

 

Duly noted, blower motor worked fine just noisy because it was full of leaves & debris

The climate control worked very well until I noticed this winter that:

The radiator tank had cracked and started leaking coolant
​​​​​​​the driver side heater was not getting very hot after the radiator was replaced
pieces of leaves were blowing out the vents
the cabin starting to smell like coolant when the heater was turned on

I cannot blame the H2 since it is 17 years old parts will be worn out an begin to fail.
I bought it as my tow rig & winter driver but I plan to keep for a while and keep it in good shape.

 

Nice work. I'd imagine the lower casing has the same slot for the cabin air filter(s) that the GM full size trucks had. My 99 GMC has a removable panel and then I think in 2003 GM decided it was useless and stopped making the little panel removable. But the slot is still molded in and can be cut open and then the filters installed anyways which a good number of truck owners do. There were two styles of the air units and one had a flat cover for the slot while the other had an L shaped cover. This is the flat one on Amazon that is advertised as for retrofitting.
One of the review even gives links to one of the truck forums which discusses the retrofit. I want to do this to mine and I also have some leaves in the airbox as well so I guess when I finally get in there to clean it out I'll find that same hole that needs to be screened to prevent leaves from getting in.

 

I have most of the dash reinstalled and tested before continuing
I reset the HVAC controller which recalibrated the actuators. I then ran it thru all the mode settings and everything works like it should.
I just need to re-charge the A/C system and this is done.

I found the same hole in the firewall on the RH side. I will have to screen that in also. my guess this is supposed to be a drain for the cowl

Next step will be re-doing the stereo install minus the PO's spaghetti wiring job. The BOSE amp is missing and replaced with a aftermarket unit. I will address this next.

 

the bose amp would be under the metal plate for the center console located between the drivers and passenger seats

 

First, What an undertaking Congrats! Could you share the holes on the firewall you are mentioning if its still possible? When i got my H2, i had the blower debris noise, caused by a rats nest in the Fresh air intake. so i pulled the blower to clean it and as much of the evap/h-Core as i could. then cut the screen to clean the fresh air intake duct under the wiper cowl, and installed a new screen Stainless fine mesh. But never saw other holes that may let debris in. Lastly did you figure any way to replace the heater core without so much tear down,now that you have it done the book way?

Thanks Sam

 

Bronx... the BOSE amp is not in there it was replaced with some other unit, and spliced into the factory harness. either this H2 was stolen in the past or a PO "upgraded" the stereo and did a lousy job.
I see some BOSE amps for our H2s on ebay.

Sam...the holes are at end the ends of the firewall cowl on each side. One is behind the washer fluid bottle, the other opposite hand. like the photos show. I would do it the same way again to replace the heater core, much easier to handle a stripped down. down dash plus I cleaned all the ductwork.

 

what door did you use for the cabin filter mod? or did you reuse the piece that was cut off the air box?