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Discussion Starter · #1 ·
The A/C in my wife's 2011 Buick Enclave stopped working due to a leak in the front evaporator. The repair quote was over $2000. Being cheap, and having more than that invested in tools, I took on the task myself. This is not so much a "how to" thread as a "what's involved". The parts are about 20% of the total repair cost. The rest would be labor. Follow along and you'll see why.
 

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Discussion Starter · #2 ·
This was where I started, the point of maximum entropy. This is the bottom half of the evaporator housing. A GREAT time to clean out dust and dirt inside.

6582
 

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Discussion Starter · #3 ·
The evaporator installed, top half of the housing fitted. In the background (right side) is the heater core and the blower motor. The blower fits in the circular opening of the evap housing. For point of reference, the blower motor ends up just above the passenger's feet and can be easily replaced when everything is back together.
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Discussion Starter · #4 · (Edited)
Blower motor installed, and Recirc/Filter housing installed. This is where the air comes in to the A/C system. It's either pulled in from the outside, or recirculated from the inside (MAX A/C) through the rectangular grill-work. The cabin air filter pleats are barely visible in the space behind that grill.
6584
 

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Discussion Starter · #5 ·
This is the other half of the system - the heater core and air-distribution plenum. All of the air first passes through the evaporator from the previous pics where it's cooled and dehumidified. The air is then brought back up to temperature by passing more or less of it through the heater core. The two square panels above the heater core are the individual doors that adjust the driver and passenger air temps. They divert a measured amount of air through the heater core to maintain the desired temperature.

6585
 

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Discussion Starter · #6 ·
The two halves are brought together and screwed tight. The lines for the heater core and evaporator all exit next to each other, in the upper left of this picture.

6586
 

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Discussion Starter · #8 ·
And this is where it goes - one blank firewall. The air comes in through the oval slot in the upper right, and the heater and A/C connections are made through the vertical, rectangular slot in the middle (the two red caps are sealing the A/C lines).

6588
 

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Discussion Starter · #10 ·
Next, the Intrument Panel (IP) Carrier. This is a single-piece aluminum casting. It's the skeleton that supports the entire instrument panel and binds everything in it - HVAC, steering column, airbags, radio, ducting... everything (kind of like The Force).
6590
 

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Discussion Starter · #11 ·
Next up, the Instrument Panel Lower Trim Panel. This is a single piece of plastic that provides attachment points for many of the buttons, switches, and wires. It also forms some of the cosmetics of the interior, hence the specific color. It's held in by 28 screws.
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Discussion Starter · #12 ·
Then the Instrument Panel Trim Pad. This is made up of several trim pieces and subassemblies (passenger air-bag, clock, ductwork), but is installed as a single unit. It's held in by 27 screws. At this point it starts to look like a car again.

Right around here I did a "howgozit" check of the remaining screws. The vast majority were identical. You didn't have to keep track of which screw went into which hole. Which was convenient. But the problem was I had 36 screws left but only 35 holes remaining. I went round-and-round several times between dashboard and Service Manual to look for that missing hole. Unfortunately, I didn't find it in my future, but in my past. It was a screw that held the HVAC system to the aluminum IP Carrier from Step 9. Luckily I was able to lift up the IP Trim Panel just enough to snake my arm in and use the Braille method to install the 'missing' screw.
6592
 

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Discussion Starter · #13 ·
The Center Console. This contains the transmission shifter, driver controls (seat heat/cool, rear tailgate and wiper, etc.) as well as the rear passenger controls (Rear A/C temp and audio/video controls for the flip-down screen). Despite this complexity it's a single assembly that installs very easily. About 16 screws secure it to the floor and instrument panel, three big multi-pin quick-disconnects satisfy the electricals, and a single cable snaps on for the shift-linkage. Easy, peasy.
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Discussion Starter · #14 ·
The steering column and radio. The radio has a lot off connectors - it controls the audio for the many speakers scattered around the cabin, along with the DVD video, CD audio, and USB connector. Plus all of the A/C controls for either front seat. They all snap together, but getting the cables to fold and fit as the radio is installed is kind of like trying to put a sleeping bag back into its original bag - you know it fit, but you're not sure how.

The steering column, on the other hand, went together smoothly. Like the center console it has multiple functions (tilt/telescope, radio/phone/cruise controls, airbag, horn) but it's all contained in a single sub-assembly. Four large bolts secure it to the aluminum IP Carrier, one bolt attaches it the rest of the steering system, and a couple of multi-pin quick disconnects connect it to the rest of the car.
6594
 

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Discussion Starter · #15 ·
And done! At least with the mechanical stuff. Mostly. The last few panels pretty much snap in place and assemble quickly. The only thing left is reinstalling the seats. Normally a quick process (two bolts and two connectors each). Except GM had an issue with the airbag connectors under the seat. The in-field fix was to cut out the connectors and crimp, solder, and heat-shrink (w/adhesive) the wires directly together. I have all the materials, just ran out time. The wires not only trigger the seat-mounted side airbags, but also the seat belt pre-tensioners that tighten up the belts in the event of an accident - safety features that I want done right, not fast.
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Discussion Starter · #16 · (Edited)
The last major step in major A/C work is replacing the desiccant. Moisture inside of an air-conditioning system is bad. It can mix with refrigerant and form hydrofluoric acid, and/or it can freeze up in small passages, stopping the A/C from working. On this car the desiccant is in a replaceable cartridge located in the condenser.

Here's the condenser, as removed from the Enclave. Air-conditioning works by having liquid refrigerant absorb heat from the passenger compartment in the evaporator (the leaking part replaced earlier). This heating causes the refrigerant to evaporate (hence the name), in the process taking heat out of the air and making it feel cold. The compressor then compresses the gaseous refrigerant, 'concentrating' the heat. It flows to the condenser pictured below where it gives up its heat to the outside air, condensing back to a liquid (hence its name). The refrigerant then flows back to the evaporator and the cycle repeats.

6596
 

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Discussion Starter · #17 ·
Here's the new desiccant cartridge being inserted into the end of the condenser. And since some oil is contained in the old cartridge, 10ml of PAG 46 oil is added at the same time to maintain the correct amount of oil in the system. The oil mixes and flows with the refrigerant, keeping everything lubricated. It's somewhat like adding oil to gasoline to keep 2-stroke engines lubricated.
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Discussion Starter · #18 ·
Condenser reassembled and reinstalled, connections made, manifold gauge hooked up and vacuum pump sucking the system empty. The desiccant readily absorbs moisture from the air, so I wanted to get the system sealed back up and pumped clean and dry as soon as possible.
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Discussion Starter · #19 · (Edited)
Vacuum! The Low-Side gauge shows pressure, and the needle can move past zero to show inches of vacuum. Here it shows 30" of vacuum (i.e. - nothing). Pulling a vacuum on an A/C system accomplishes several tasks. First, the system works best with pure refrigerant. Air just gets in the way, reducing efficiency. Second, water boils at room temperature at such low pressures. Any moisture left behind readily evaporates and gets drawn out by the vacuum pump. And third, it serves as a simple 'leak-check'. I ran the vacuum pump for an hour that night, then closed the valves. The picture is from the next morning, still showing a hard vacuum which means no leaks. Now a system may be tight under vacuum but leak under pressure, but there's no way to test that until the system is operating. Even so, this is a good "howgozit" step.

All that's left is putting the seats back in. But that I can do while waiting for the refrigerant to flow back into the system.
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Discussion Starter · #20 ·
And... it's done!

I put the seats back in, recharged the system, turned the key...

...and the dashboard lit up like a Christmas tree with warnings and lights.

Traction control, ABS, stability control, airbags. It looked like every warning light was lit. I plugged in my code scanner to try to make sense of it all. One error caught my eye: "MAF (Mass AirFlow) Sensor". Hmm, I had to remove the MAF to get at the AC and heater hoses on the engine side of the firewall.

So I checked under the hood - the connector to the MAF was in place, but I put my hand on it, gave it a push... and the connector audibly clicked as I pushed it home. I cleared the codes, restarted the car, and all the warning lights and messages went away (Yay!)

It makes sense because in order to provide traction control, stability control, and ABS, the computer has to know exactly what the engine is doing and be able to control it. With the MAF sensor disconnected the computer lost a key insight. The MAF tells the computer how much air is going into the engine. Without it, the computer has to infer airflow based upon throttle position and RPM - good enough to drive home, but not good enough to manage power properly.

However, one error message still remained - the airbag. (boo!)

But this one was not unexpected. There was a recall on this vehicle. GM had a problem with the airbag connector under the seats corroding in service. The in-field fix was to cut out the connector and twist, crimp, and solder the wires together. This was done to this vehicle already. So when I removed the seats I had to cut the four airbag wires (two for the side airbag, two for the seat-belt pretensioner).

Here is how the wires are reconnected, per the recall notice. From left to right the wires are folded, crimped, soldered, then sleeved with adhesive-lined heat-shrink tubing.
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