Removing rear AC lines at evaporator

[KVacek]

2005 Yukon Denali XL
Need to replace the seals at the rear evaporator connection, under the vehicle, but cannot get the connections free. Nuts came off fine and I've tried heat and penetrant, but the connection aluminum blocks are seized on their studs. Asked a great independent shop, he said nobody can get them off. Had a local automotive radiator and A/C shop try but they gave up too.

I have a set of new lines on the way (I'll eventually need them anyway I'm sure), but is there any trick I should try first to get these off intact?

 

[sumo]

Forget about it. I broke mine too and ended up having to order a New rear Evap. I even had my old one benched and did everything to try and separate it.

 

[KVacek]

Ummmm, thanks for the bad news ;-) As I figured...
To get the old connectors off the evaporator I was just going to slice across the aluminum along the stud. Gotta come off then, doesn't it?

 

[KVacek]

They weren't seized on the studs as much as the seals having welded themselves onto both parts.

If you need to do this job, it's probably not as hard as it seems. After lots of heat and dry ice (thermal cycling), and a trip to an A/C shop that couldn't get the lines off either, I persisted and eventually got them off. The corrosion in the stud holes through the connectors was likely not a real issue, though heat cycling probably helped break it loose.

First one came off with lots of heat, which appeared to mostly melt the seal. The second one came off with lots of trichlotoethane (Brakleen), which is a good solvent for the HNBR seals, and ate the rubber seal loose. I did pry a bit. Cleaned up with Brakleen, a brass brush, and ScotchBrite. New seals with blue Nylog, lots of antiseize on the studs, vacuumed and charged, 1 oz of PAG 46 oil for good measure, and it's fine. Cold A/C.

I had ordered a set of new lines (from an advertiser on this forum) figuring I'd have to cut off these connectors, but the lines came later than promised and I'd already given up on them coming in time. Package unopened, going back tomorrow.

 

[KVacek]

Epilog...
The heat apparently melted the factory seal in the evaporator at the junction of the high side tube and the connecting block. Evaporator was slowly leaking and 134A/oil stinks. Held vacuum OK but lost charge in a few days. New GM evaporator comes with a new expansion valve too, so I just spent the money on a new evaporator rather than having the old one TIG'd. Taking the rear HVAC case apart is a real treat - especially the 4 screws that go in from the underside. Might almost be easier to pull the heater hoses and remove the whole thing, but no, not me... If you need to do the job without takiing the whole unit out, I highly recommend making yourself a mini ratchet wrench for those four 7/32 screws. Get a nutdriver bit and a 1/4 ratcheting box wrench (GearWrench etc). Cut the nutdriver bit down so there's no extra 1/4 hex bit projecting below the ratcheting box wrench, and you'll save some time. I didn't have a cheap bit and didn't want to ruin my set, so rather than spend time running out for one I just used ignition wrenches for that hidden one in the rear. 12-point ignition wrench helps there but it's a pain in any event...