'99 c2500 Burb fun

[rockR67]

Hi all,

I've been working on this c2500 7.4 Suburban quite a bit across the summer, so I figured I'd go ahead and start posting some progress along the way. As a first step, the subject in question:
8/30/23
LA

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There's some work to be done here but it's in pretty good shape. The truck spent most of its life in Iowa, but wasn't driven much in the winter months (thanks mostly to the 2wd setup I think). Across the past few years it got some decent maintenance like new intake manifold gasket work so it hasn't been ignored either.

So what to do?
- The a/c was relegated to front only. That's not acceptable in Louisiana.
- The compressor was replaced, twice, but is still leaking. HT6 problem there I think.
- Headlights are deeply fogged.
- Front vents don't work
- Radio has lost its nobs, and it would be nice to get an updated unit anyway. For now, I've put a FM Bluetooth unit in so I can connect a phone.
- Running boards need help
- Rims need some help
- I'd like to get a front air dam in place (I kind of like the look of them on the 4x4s with tow hooks)
- Tow mirrors needed, I'd like to put this to work on our 24' Hi-Lo that I've restored

So I'll get this thread going and post some pictures of progress. A shot of the headlights is below for reference.

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[someotherguy]

Great trucks. For a while I was on the lookout for a C2500 7.4 'Burb but couldn't find one that suited me (most I found were 4x4), so I got the C3500 7.4 dually instead.

Richard

 

[rockR67]

Great trucks. For a while I was on the lookout for a C2500 7.4 'Burb but couldn't find one that suited me (most I found were 4x4), so I got the C3500 7.4 dually instead.

Richard

I've actually had a soft spot in my heart for those too. Nice, tough trucks.

 

[rockR67]

An update for the thread here: after thinking through the list I decided that I would fix the inside air vent problem first, then move out from there. It also seemed like the most unpleasant of the jobs because of the significant interior disassembly required. Hats off to those who can pull the interior in a couple of hours!

Below, one of the problems identified: missing hvac box linkage that has been replaced by a zip tie...?!? Wow.

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That's the vent controller motor that you're looking at there, and the vents that are facing the camera are heater vents to the floor by the drivers seat. It's an interesting view up behind all of that if you've never stood on your head to do it before

Now, I highly recommend several youtube videos on the actual way to disassemble these things. And take your time. And don't forget you'll really want to remove the drivers seat and pull it way back or out just to get the steering wheel to drop enough. Even if you think that you don't need to. Just sayin' ....

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Found a good use for some cans of dog food too along the way...

View from the top down with the dash rolled forward. Now we've got the top of the vent box exposed. Too bad there's still no way to work on it. Also too bad that it was 100F in the 'burb when I was working on this too.

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Meanwhile, over on the other side of the firewall, several screws to remove that are all behind a/c components and heater hoses to the heater core and a bolt that's easy to forget about. Two other bolts behind the engine itself are holding the whole thing to the firewall. Good opportunity to clean some stuff up over here too while we're at it. Next, pulling the HVAC box apart, restoring and reinstalling.

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And with all of that done, it eventually can be dropped to the floor and 'eased' out of the interior. A simple 43 step process.
The passenger isde view of it pulled back from the wall, ready to exit (with some effort) the passenger door and be completely re-habbed. Note that we have dog food on one side of the truck holding the steering column / wheel, and a 12 pack of seltzer on the other side supporting the rotated and pulled back dash on the other. I've actually seen a photo somewhere that has this passenger side of the dash being held by a strap to the grab handle above. Great idea, wish I had run across that before I went for the seltzer water solution.

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[Pinger]

Unsticking the blend doors on my 99 'Burb is on my to do list. The actuator works - I can watch it move - but the output is only available at the screen and footwell heater ducts. Will I have to do what you've done to get it working?

 

[rockR67]

Unsticking the blend doors on my 99 'Burb is on my to do list. The actuator works - I can watch it move - but the output is only available at the screen and footwell heater ducts. Will I have to do what you've done to get it working?

Good question. It sounds like you're missing the upper defrost? If you can see all of the actuators move (there should be two levers and the motor is direct-drive on a third door that operates the heater vents at your feet), then I'm not sure. If there's a link missing, that should be replaceable without this dissassembly.

The disassembly comes when a door falls into the box and off its pin (hinge). Or the seals are so bad around the old flapper doors inside that the air goes most anywhere it wants anyway. Honestly, it sounds like you've got something stuck, probably the top lever that cuts the defrost in/out.

Taking this stuff apart requires draining the radiator fluid (heater core is in the box) and also removing the refrigerant (evaporator core is in the box). It's a mess, but doable. Just give yourself time. I've got some pics of the box itself to post soon too, so I'll keep going with this project and you'll get a better view of at least a few things.

 

[Pinger]

Mine is stuck. I get defrost to the screen and can combine that with heat to footwell but when I move to shift the air flow to the vents (eg, the ones that are aimed at the face) I can see the actuator move. What happens though is that the airflow ceases to go to the defrost and footwell but doesn't appear at the face vents. Instead, I hear the fan working harder as the flow backs up.
Really don't want to have to strip the dash out for this.

 

[rockR67]

Hi All,

Thought I'd walk through a few more pictures of fun with the hvac. In the end, my assumption that this job would be worse than the other problems was right but it's not impossible. Here's a photo of the system in question tossed out on the ground, because that's how I felt about it at the time:

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It's laying on its side, so the connections pointing up are the heater core (bottom two) and evaporator. This is also a really good time to replace all of those flapper valve actuators (there are three) since they're easy to get to.

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Here's the main vent box removed and disassembled. If there's something jammed, it could well be that one of these flapper vent doors has fallen off its pin-hinges and gotten stuck. Amazon has new assemblies for the top half of this thing so I went that route. It is possible to just buy new doors and put it together though from what I could tell. Below is the other half of the box, also disassembled. New heater core in place, new evaporator in place.

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Make sure it's plenty hot outside with lots of humidity whenever you work on this ...

Cleaned up the firewall and engine bay a bit while I could get to it all, and after a lot of (unrecorded) messing around you can see the box is back inside the truck with heater core (lower connections) and evaporator stick through the firewall as they should. Make sure it's as hot and miserble as possible when attempting this part of the job too.

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So about this time I noticed that the radiator hoses felt squishy and original so I thought it would be a good idea to replace those too, and the heater hoses with them. It couldn't possibly take more than a few minutes anyway.

Until GM decided to turn all of the clamps towards the engine, or towards the frame at the lower radiator connection. Trust me when I say there was no way this was coming off. So a 20min job was two hours with very careful and slow progress made with a dremel tool.

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So it went back together, next it's a/c compressor and rear evaporator time. I learned the rear was disconnected for a reason, so that's next.

 

[Orpedcrow]

Heckuva project you’ve undertaken but good on you for doing it. Keep us updated!

 

[rockR67]

Thanks for the encouragement folks - this thing has been a project but it's getting there. Here's the next round of progress:
With the front HVAC reassembled, and radiator and heater hoses replaced ... time to reconnect the rear air. From my understanding, this was disconnected a few years ago using one of those cut-out kits because it was leaking badly from back there.

So into the back of the truck we go and some panels to remove:

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25 years of dust and dirt

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GM was thoughtful enough to put the a/c lines that feed the evaporator WITH their connections directly up and behind the rear wheel. I assume this was to ensure they were always kept well washed down and clean, making them easy to remove from below ... however, the brilliant plan seems to have failed because it left them unfortunately corroded or attacked by whatever road grime had left its mark

My solution was to get the rear HVAC black box released slightly and elevated so the connectors could be accessed from inside the suburban. It was easier to get wrenches on them this way and apply enough torque to get them apart. I'm sure bathing them in PB blaster helped too. I started that several evenings before actually attempting this and used some of the scrap wood to help keep it above the carpet line for the wrench access.

I was fortunate that despite their location behind the rear wheel - the truck wasn't driven that much in salty mid-west winters. So it at least had a chance.

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Note for anyone who ever does this: The top "small" supply side nut does not spin - or mine certainly wasn't about to (the larger diameter hoses are return line). This is actually a piece that connects directly to the thermal-expansion-valve (TXV) hidden in the black box, connected to the evaporator. It will round off easily... Just grip it with vice-grips and get it done by spinning the lower connector off. Here's a picture of it and the evaporator removed from the HVAC box - it's the lower left connector.

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Removed unit below with heater core and fan removed. I opted to leave the heater core out and plumbed out the heater lines from the front. Less future problems with old heater hoses and connectors.

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So, everything back together and plumbed and tightened down. Now to evacuate and charge with a new Sanden to install too... more in a bit.