AC System Differences

[Dreddy1]

I've got to get my AC working again on my Cummins swapped 96 burb. I've used the stock components after the swap and while the AC wasn't great prior to the swap, its completely broken now. I used to have a 99 burb in which the AC actually worked pretty well, at least there was some air flow through the vents which is almost non-existent in the 96 model. Does anyone know if there are differences behind the dash with these models? (96 -> 99) I'm going to probably take a significant portion of the dash off to install a new evaporator and was wondering if there are other swappable parts that could make a worthwhile improvement to the interior comfort. This would be my ultimate boat towing rig if I could just get this done right.

 

[Schurkey]

FIRST you need to define "completely broken".
Exploded compressor? Electrical fire? Refrigerant leaked out slowly? Hose ruptured?

What is the system pressure with the compressor NOT running? Does the compressor run? What are the pressures (high side and low side) with the compressor engaged?

Does the fan run on all of the speeds? Does the air come out the correct vents as the switch is moved from floor to defroster? If you have any problem with the amount of air coming from the vents, I would put a low-ampere probe on the fan power wire, to verify the amount of current it's drawing. My '97 K2500 had a fan motor pulling so much current, I had smoke coming out the dash vents, and it popped the 60-amp MaxiFuse along with the (20 amp???) A/C fuse, and also popped the thermal fuse that's part of the resistor block. Each time I found a popped fuse and replaced it, the next fuse in the circuit was shown to be bad, too. Obviously, I stuffed a blower motor and fan into the HVAC box, too.

Any chance the evaporator case is plugged with leaves, mouse nests, pine needles, etc? You can see some of it with the blower and fan out of the way.

Wild Guess: At minimum, you need to replace every O-ring in the system, the desiccant pouch (accumulator) and the orifice tube. Some folks like the larger Ford orifice tube. Worth researching. If you're going to open the evaporator box, obviously you're going to clean out all debris. Verify that the air fins on the condenser aren't folded-over or corroded.

 

[kennythewelder]

FIRST you need to define "completely broken".
Exploded compressor? Electrical fire? Refrigerant leaked out slowly? Hose ruptured?

What is the system pressure with the compressor NOT running? Does the compressor run? What are the pressures (high side and low side) with the compressor engaged?

Does the fan run on all of the speeds? Does the air come out the correct vents as the switch is moved from floor to defroster? If you have any problem with the amount of air coming from the vents, I would put a low-ampere probe on the fan power wire, to verify the amount of current it's drawing. My '97 K2500 had a fan motor pulling so much current, I had smoke coming out the dash vents, and it popped the 60-amp MaxiFuse along with the (20 amp???) A/C fuse, and also popped the thermal fuse that's part of the resistor block. Each time I found a popped fuse and replaced it, the next fuse in the circuit was shown to be bad, too. Obviously, I stuffed a blower motor and fan into the HVAC box, too.

Any chance the evaporator case is plugged with leaves, mouse nests, pine needles, etc? You can see some of it with the blower and fan out of the way.

Wild Guess: At minimum, you need to replace every O-ring in the system, the desiccant pouch (accumulator) and the orifice tube. Some folks like the larger Ford orifice tube. Worth researching. If you're going to open the evaporator box, obviously you're going to clean out all debris. Verify that the air fins on the condenser aren't folded-over or corroded.

Everything He said plus, if you going that far, you may as well replace the resistor and fan. I replaced mine a few months ago, and I was very suprised how big of a difference it made. As for a difference between the 99 burb, and a 96 burb, they are the same unless one has dual air, and the other does not.

 

[Schurkey]

if you going that far, you may as well replace the resistor

The resistor pack is essentially three resistors and a thermal fuse. If the resistors aren't melted so as to create an open circuit (fan won't run on all speeds) and the thermal fuse is still good (fan runs on all the lower speeds; high speed bypasses the thermal fuse) then there's no reason to change the resistor unit.

This photo is from my '98 Monte Carlo, which also failed the thermal fuse. I don't seem to have a photo of the resistor pack from the '97 K2500. The HVAC box "duckbill" plugged on the MC, the box filled with water, and the resistor pack electrical connection rusted so bad it couldn't be pulled apart. Everything is rusty-colored because it's full of rust and sediment.

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With the '97 K2500, I started at the 60-amp MaxiFuse, then found the HVAC fuse, at which point the motor would run on high speed, but smoked. New motor/fan fixed the smoking, but still only ran on high speed until I put a jumper wire across the thermal fuse of the resistor pack, in which case everything was good--Low, M1, M2, and High speed all worked as they should. New resistor pack--for the thermal fuse, not for the resistors themselves--and it's all back together and working good.

Of course, while the fan was out, I pushed some compressed air backwards through the Evaporator, which released a few pine needles and other leafy debris.

and fan.

My fan motor had winding that were burnt black, as I said, I had smoke from the dash vents. Amazing it even ran at all. Yeah, replacing the motor and fan (they're sold as an assembly) was essential.

But if the resistor pack and the motor/fan aren't bad...why replace them?

For the record, I found with my '88 K1500 that the NAPA HVAC fan motor was smaller and spun slower than the ACDelco fan motor. I've been buying ACDelco "OEM" HVAC motors ever since. This discovery was near 20 years ago; things may have changed since then.

 

[kennythewelder]

But if the resistor pack and the motor/fan aren't bad...why replace them?

Well my 97 fan got to where it would only run on high. Then it quit all together, so I replaced the resistor. All good but then the bearings in the fan started making noise. For a long time, the amount of air coming out of the vents sucked. After replacing the fan, it was a night and day difference. I figure like a fuel pump does when it gets old, and weak, so does the fan. It just isnt turning the RPMs like it did new. By changing both resistor and fan, you know your back up to par. Granted I have cleaned out the HVAC box, but that was before I changed out both fan and resistor. Also as old as the trucks are becoming, if its the OE fan and resistor, its seen better days Im sure.

 

[Dreddy1]

Thanks for the read on this everyone.

By broken, I mean that there is absolutely no cold air coming from the system. During the swap, I put everything back in place, and had to replace the supply line to the condenser and did the condenser at that point, cleaned out everything I could from the evaporator, replaced the refrigerant, etc. It was cool for a few days, and then went back to blowing hot. This was with a good vacuum out and leak-down. I'm obviously not an AC expert. I think I should take the advise to replace every seal in the system and try to get it back to working condition, however, I just have this feeling that it is still going to suck no matter what i do. I will dive into the fan and resistor question as well. I didn't really consider the possibility that they could simply degrade over time. thanks for the ideas.

 

[Dariusz Salomon]

Welcome to AC hell. I had to replace nearly everything in my system-I have dual AC and I was stubborn to make it work as it should. My truck's ac wasn't workin when I pught it-guy said"I had it a year and never bothered with it". So I assume guy before him never bothered too. And when it's not used for so long nearly all seals and stuff perish
I started with replacing condenser,orifice tube,some seals. Worked for a day and the compressor went(belly leaker)-I changed that-upgraded it to a different design one-much better and safer(can't remember what name and model of top of my head). After that valves went. Changed those. Then radiator. Changed that. Then pipe that runs to the back-fixed that-went in another place. Replaced it with 10mm copper pipe. Finally it holds. If you need any assistance feel free to ask. I attach link-it was really helpful in ac refurb for me. Good luck

https://dorkiphus.net/porsche/showthread.php?t=26215

 

[Dariusz Salomon]

Sanden compressor I replaced it with-by UAC-it's got a different construction(original is 2 body halves sealed in the middle and that's weakest point).
And the best way to find the leak is to put die in the system-then the UV light and check everything. Vacuum from the machine will NOT show small leaks-tested it.

 

[1998crewcab]

you could check to make sure your AC relay is getting power
Then measure voltage at compressor
If you see 12 volts on one leg
Then you have a ground issue
With Ac system on .

before tearing back into it
Get some gauges to see where you are as far as pressure
I don’t think it leaked per your information

 

[Dariusz Salomon]

you could check to make sure your AC relay is getting power
Then measure voltage at compressor
If you see 12 volts on one leg
Then you have a ground issue
With Ac system on .

before tearing back into it
Get some gauges to see where you are as far as pressure
I don’t think it leaked per your information

Since he said it was blowing cold and stopped-tho I don't know if gradually or suddenly) I assume it's not electrical but everything's possible.