Heat box swap

[79kcrew]

Has anybody done or attempted to swap the heat box out of a 99-07 Silverado? Just not happy with the factory system and I’ve got a couple parts trucks (99-07) laying around, so it’s something I was pondering.

 

[SquareRoot]

Has anybody done or attempted to swap the heat box out of a 99-07 Silverado? Just not happy with the factory system and I’ve got a couple parts trucks (99-07) laying around, so it’s something I was pondering.

1st post. Welcome. Don't be a drive by, stick around and engage a bit. First of all, define "Heat Box". You talking about the heater core enclosure?

 

[TotalyHucked]

Not something I've ever encountered. What don't you like about your original unit? It may just need a revamp, the heat in my '85 will run you out

 

[idahovette]

^^^^^^^THIS, there ain't nothing like a Chevy heater^^^^^^^^^

 

[Catbox]

Welcome and I think you should do it and chronicle your efforts here with loads of photos.

 

[Originalthor]

Welcome and I think you should do it and chronicle your efforts here with loads of photos.

I agree. I always wondered if they would fit under our dashes. Just controlling it my be tricky

 

[79kcrew]

Not something I've ever encountered. What don't you like about your original unit? It may just need a revamp, the heat in my '85 will run you out

Just poor output, last winter I had to pull over and scrape ice off the windshield a handful of times in roughly 25 miles. Replaced motor, resistor, and speed switch. Pulled the heater core and hosed it out as well.

 

[79kcrew]

1st post. Welcome. Don't be a drive by, stick around and engage a bit. First of all, define "Heat Box". You talking about the heater core enclosure?

Yes the whole enclosure, my thought was to try and swap essentially the entire system, climate control and all over since I’m already running a 5.3L and have everything in place to run it with minimal wiring modifications

 

[gmbellew]

I think you might have a blend door issue or something wrong in the vacuum controls. The heat in my 90 burb is intense and the air flow on heat (floor) and defrost (top of dash by windshield) is pretty strong.

 

[79kcrew]

I think you might have a blend door issue or something wrong in the vacuum controls. The heat in my 90 burb is intense and the air flow on heat (floor) and defrost (top of dash by windshield) is pretty strong.

The thought was to use the entire box with the electric blend doors

 

[TotalyHucked]

Where are you located out of curiosity?

There's so many things that simply won't work swapping an NBS heating system into a square. Your time would be better spent trying to figure out why you don't have good heat in your original setup. A properly working original heater should do everything you need unless you live up in the artic circle, but then no vehicle will have enough heat without mods.

What's your current setup? You mention you have a 5.3 in the truck, so do I. I still have my original heater box but I did have to put a new heater core in it because mine was partially clogged and leaking. After I did that, my heat got even better.

 

[TotalyHucked]

I've had 7 of these trucks, so I'm very familiar with them. When I say there's many things working against you, I mean the firewalls are totally different shape and opening-wise so the box isn't going to be a drop on deal. Then you have the matter of controlling it, I believe the HVAC was at least partly controlled by the BCM. Some NBS trucks were digital AC control, some were manual sliders and the complete HVAC system is different. Box, controls, layout, everything. There's also the blend door actuators (there's 3), one behind the gauges, one down low in the middle and one up high behind the pass airbag. Think about how big the dash is in one of those trucks to fit all of that, it's never going to fit in a square.

 

[75gmck25]

My K25 came from family in North Dakota, and I’m now in Virginia. I have never suffered from a lack of heat in the truck.

What temp thermostat do you use? I have a 195 degree thermostat (stock for my engine) and it usually keeps the engine at about 190 in the winter. I don’t block off the grill or make any other winter mods. I have an HD fan clutch, so I’m not sure it ever stops the engine fan completely.

Do all your vacuum controls and actuators work? IIRC, with no vacuum for the actuators on the heater box, it defaults to splitting the air between heat and defrost.

 

[scrap--metal]

Yes the whole enclosure, my thought was to try and swap essentially the entire system, climate control and all over since I’m already running a 5.3L and have everything in place to run it with minimal wiring modifications

This isn't necessary... These squares have been melting the coldest of ice since the day they left the show room.

Something is farqued with your heat...

Do all your vacuum controls and actuators work? IIRC, with no vacuum for the actuators on the heater box, it defaults to splitting the air between heat and defrost.

^ I'm pretty sure this is correct. Before I hooked the vacuum line up in my K20, the vent would blow harsh warm air in the summer heat.

I did have to put a new heater core in it because mine was partially clogged and leaking. After I did that, my heat got even better.

Pulled the heater core and hosed it out as well.

^ And this stuff here... You'll never clean a heater core out well enough if it's already compromised with gunk.

Check the vacuum line going into your firewall like @75gmck25 suggested (assuming you know it's connected under the dash). If that's intact, I'd bet the heater core is to blame.

Please follow up and let us know what you find.