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Rear AC repair info: Yes, it has a Thermal Expansion Valve (TXV)

WarWagon

Well it hits on 7 of 8...
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One of those little things you find to help understand the system and repair info to boot! Specific to a problem with 1994-1995 years but can apply to other years.

http://www.alldata.com/service_provider/techrx/2001/20010703f.html

Don't Knock Until You Try It
GMC Suburban A/C Compressor Knock
Last year about this time, a very nice customer named Jeanette brought her 1995 GMC® Suburban® into the shop complaining about a knocking noise.

"It sounds like the noise is coming from the A/C compressor, but the A/C still seems to work fine," she said. "I just started using the air conditioner last week and that's when the noise started."

"That is an important observation," I said. "I'll note that on the repair order. The technicians like to have as much information as possible to help diagnose these kinds of problems."

As she was waiting for our shuttle to give her a ride home she asked, "Have you ever had sweet potato ice cream?" "No, and that sounds sort of weird," I replied. "Don't knock it until you try it,"
She said. "I make the best, award winning sweet potato ice cream anyone's ever had. In fact, I'm making some today for this year's county fair exhibit. I'll bring some back for you," she related. "That would be great," I said. "I'll try to keep an open mind."

When we got the vehicle into the shop, the technician said he thought he remembered seeing a technical service bulletin that addressed this problem. He was right. A quick check in our ALLDATA automotive information system revealed a bulletin that listed the same symptoms for 1994 and 1995 GMC® Suburban® models built before the vehicle identification number breakpoint of SJ701253 and equipped with Rear A/C only or Rear Heater and A/C systems.

The bulletin went on to describe the cause of the problem. When the rear A/C system is shut off, a refrigerant flood back condition may occur through the rear A/C system. This flooding degreases the internal parts of the compressor resulting in rapid slider block wear and the resulting loud knocking noise. A poor contact between the Thermal Expansion Valve (TXV), capillary tube and the rear evaporator outlet tube can allow the TXV to remain open when the rear system is not in use. The open TXV may allow liquid refrigerant to flood back through the rear system (liquid line, TXV, evaporator, rear suction line) and subsequently flood the compressor.

After listening to the compressor to verify the complaint, I called her to get the okay to do the repairs. She agreed and we went to work. Here is the service procedure the bulletin described, which involved replacing the A/C compressor, the TXV, and adding an in-line filter.

Service Procedure
1. Recover the R-134a refrigerant charge.
2. Replace the compressor and balance the lubricant in the system.
3. Install an in-line filter in the liquid line after the condenser and before the "Y" in the line separating the front and rear systems.
4. Remove, inspect and clean the orifice tube for the front system. It is located in the liquid line after the "Y" joint.
5. Replace the orifice tube.
6. Disconnect the seat belt and remove rear bench seat.
7. Remove the right second passenger seat shoulder belt retainer from the right side C-pillar.
8. Remove the (5) screws from the right side C-pillar trim.
9. Remove the (2) screws securing the right side lower trim panel to the C-pillar.
10. Remove the (5) screws securing the D-pillar covers.

See Figure 1.

11. Lift the right side lower trim panel and roll forward to remove, this exposes the rear HVAC evaporator case module.
12. Using a template (See Figure 4), mark cutting lines on the upper evaporator case using a china marker or equivalent. Do not remove the locating tabs from the templates; they are needed to position the cut area for the access doors (See Figure 1).
13. Using a template (See Figure 5), mark cutting lines on the lower evaporator case using a china marker or equivalent (See Figure 1).
14. Cut through the plastic upper evaporator case and the lower evaporator case following the marked outlines of the templates to create two access doors (See Figure 1). Do not cut rear edge of either access door (See Figure 4 and Figure 5). Use a hot knife or a small (1/2" dia.) rotary abrasive cutting wheel.

Notice: Cut through plastic case material only. Aluminum tubes are located approximately 1/8" behind the case wall (See Figure 2 - view 1).

15. Using a heat gun to soften the plastic case, pull back the access door on the upper evaporator case carefully to prevent breaking the case. Reach in carefully and remove the holding clamp securing the capillary tube to the evaporator outlet tube. Be careful not to damage the capillary tube. Discard the clamp.
16. Using a heat gun to soften the plastic case, pull back the access door on the lower evaporator case carefully to prevent breaking the case (See Figure 2). Reach in carefully with two small adjustable wrenches and loosen the fitting attaching the TXV to the evaporator inlet tube. It will require a 7/8" crow's foot extension to loosen the TXV outlet joint fitting hidden behind the TXV itself. Remove and discard the TXV.
17. Remove original O-rings from the evaporator tubes and replace with new O-rings that have been oiled with 525 viscosity refrigerant mineral oil. DO NOT USE PAG LUBRICANT.
18. Install the new TXV to the evaporator tubes being careful not to damage the O-rings. Finger-tighten the joints and then torque the joints, using a backup wrench to hold the TXV in position to:

Inlet: 20-35 Nm (14-25 ft. lbs.)
Outlet: 15-22 Nm (11-16 ft. lbs.)

19. Pull back the access door on the upper evaporator case carefully to prevent breaking the case (See Figure 1). Align the TXV capillary against the evaporator outlet tube being sure not to damage the capillary line. Place the first holding clamp so it is located 1/4" or less below the crimp in the capillary tube (See Figure 3). Install the second clamp 1/4" or less below the first clamp. Be sure the clamps are fully seated on the tube and that the capillary is retained in the formed seat of each clamp (See Figure 3).

Notice: After all components are installed, evacuate and charge the A/C system. Leak test all joints that were opened.

20. Using a heat gun to soften the plastic case, close both access doors and align the edges of the plastic. Using a soldering gun, melt both edges of the case together along the full length of the cuts, as smoothly as possible.
21. Cover the soldered closures with duct tape to prevent air leakage.
22. Reinstall the right side trim panel, the D-pillar trim, the C-pillar trim, the C-pillar seat belt retainer and the rear bench seat.

We completed the repairs described in the technical service bulletin. And by the time we were done, the afternoon temperatures had climbed to 90 degrees. Jeanette came to pick up her Suburban with a half a gallon of her sweet potato ice cream in tow. "You just have to try this," she said.

I'm not sure if it was the heat or curiosity that prompted me to agree to a taste test, but I'm sure glad I did. She was right. It was some of the best tasting ice cream I ever had - sweet potato or otherwise. I called the technicians into the office to share in my good fortune. Five minutes later, I was standing at the counter with an empty ice cream carton. I handed the keys to Jeanette, my technicians' new hero and she was on her way. We're all counting the days until her next scheduled service.
 
And after the compressor grenades... You CAN NOT SKIP REPLACING THE TXV VALVE! (Some shop did this before me and the compressor ate valves. Flushing will not work - I tried it.)

Also you do not need to cut the case. With the proper tools, extensions, and u-joint you can remove all the 5.5MM case screws even on the backside. You may have to move the case over at the top 1-2" with help to hold it for the last screw. It is best to leave the evaporator in place to change the TXV as the nuts tend to rust on the bottom of the evaporator under the vehicle.

IMO you should also replace the condenser.

Lets have a look at debris big enough to read part numbers in the TXV screen. Screen is on the left and O-Ring on the right with the brass TXV valve.

100_3553.jpg

100_3551.jpg

The water catching screen is also very dirty.

100_3556.jpg
 
Not as bad as mine was when I did it. Be careful as teh replacement expansion valves don't come with a screen in them anymore(don't ask how I know).
 
Would you recomend installing a filter upstream in an accessable location.

It's always a good idea to add a filter after the condenser after a compressor failure. Unfortunately though, the debris is normally throughout the whole system by the time you know you've had a compressor failure.
 
Pic of evap housing. Relay pack is behind the foam on top of the housing not shown. The side has those irritating spring clips at the top just below the window. Evaporator is removed at this point. Expansion valve is located on the inside and can be changed with a crow's foot. Buy the tool! Otherwise the threads for the evaporator can be ruined as they may have welded themselves to the steel nuts.

You can see the 3 relays in the pic, but, they were moved to get the top housing off.
rear evap.jpg

Motor and resistor pack can be serviced with removal of the intake grille only.
rear evap2.jpg
 
Other info:
The R-4 compressor displaces 11ci. Or 180.26cc.
The R4 takes PAG 150 OIL and will not tolerate Ester oil. (R134a)
Always buy a NEW R4 compressor. Look at how big (labor time) and expensive this job is. Reman R4 compressors are known to blow up and when they do you get to do the job over again or pay someone...

Do not run the system low on freon or the compressor starves for oil and makes a mess in your system.
Cooling system is also important to AC life. Fan clutch less than 5 years old and clean condenser/radiator. Pull the oil cooler and check for a mat behind it as these build one up.
 
System capacity with rear air 1995: 64oz aka 4 LBS 134A, 11 oz PAG 150 oil.
 
No VOV use in dual air

The Variable Orface Valve is about 1/4" too long to use in the dual air system vs. the standard shorter factory orface tube. The pipe stands out preventing the o ring from sealing if you could even get a thread on the connection. This is because the VOV sticks out 1/4" too far after it is seated on the dimples in the pipe.

It may be possible to replace this section of pipe and use a VOV.
 
The Variable Orface Valve is about 1/4" too long to use in the dual air system vs. the standard shorter factory orface tube. The pipe stands out preventing the o ring from sealing if you could even get a thread on the connection. This is because the VOV sticks out 1/4" too far after it is seated on the dimples in the pipe.

It may be possible to replace this section of pipe and use a VOV.
I ran one in mine for awhile, fit just fine. Didn't work good going down the road, but worked great at an idle.
 
The only way to get the VOV to fit the rear air units is to trim the tabs off the black cross stop. Then it fits by extending into the evaporator tube.
 
The only way to get the VOV to fit the rear air units is to trim the tabs off the black cross stop. Then it fits by extending into the evaporator tube.
I have the one out in my tool box I bought from NAPA that I ran in mine, and didn't trim it any. Fit in just fine. It looked like it wouldn't, but it did fit. On the other hand, you should never run 2 variable orifices/valves in an A/C system as they will begin to work against each other.
 
Experimenting with a heater block off valve and a VOV trimmed to fit got me 49 degrees at the front center vent and 55 degrees out of the rear 2nd seat vent with a 21% humidity 111 degrees out while engine was at idle.

The manual heater coolant valve is only like $10 at your local auto parts store.
 
I'll be doing my dual HVAC system soon, I had cheated last time I did the expansion valve by dremel cutting the rear ac case to access it worked just fine but had a compressor fail this time around and need to change out compressor manifold & hoses which I located at RockAuto for the 1999 K3500 cab chassis dual ac ambulance package it's the same as my Burb's setup which everyone says can't be had.

I'm going to a very large condenser that the K3500 cab chassis has for the ambulance package it measures 35 7/8" wide by 17 3/8" making it almost 30% larger than the big condenser FERN suggested in the performance forum, the switch to BIGGER requires I adapt my threaded fittings to the block style condenser fittings (aka: peanut fittings). This condenser is just as big in frontal area as the Ram Cummins CAC/I I'm installing.

Another suggestion FERN has is to use a TXV in place of the orifice tube when going big on the condenser so I need to learn more about doing that and thinking to install a filter dryer or accumulator for the back AC too.

Suggestions and thoughts from those of you in the know are welcomed with open arms.
 
I'll be doing my dual HVAC system soon, I had cheated last time I did the expansion valve by dremel cutting the rear ac case to access it worked just fine but had a compressor fail this time around and need to change out compressor manifold & hoses which I located at RockAuto for the 1999 K3500 cab chassis dual ac ambulance package it's the same as my Burb's setup which everyone says can't be had.

I'm going to a very large condenser that the K3500 cab chassis has for the ambulance package it measures 35 7/8" wide by 17 3/8" making it almost 30% larger than the big condenser FERN suggested in the performance forum, the switch to BIGGER requires I adapt my threaded fittings to the block style condenser fittings (aka: peanut fittings). This condenser is just as big in frontal area as the Ram Cummins CAC/I I'm installing.

Another suggestion FERN has is to use a TXV in place of the orifice tube when going big on the condenser so I need to learn more about doing that and thinking to install a filter dryer or accumulator for the back AC too.

Suggestions and thoughts from those of you in the know are welcomed with open arms.
No, you DO NOT run a TXV on a dual air system for the front, you only run an orifice in the front and a TXV for the rear. And cutting the box to access the rear TXV is the reccomended method by GM due to the problem of the rear lines seizing to the fittings underneath the rear HVAC. In a dual system you either run 1 orifice and one TXV, or 2 orifices, but NEVER 2 TXV's as they will end up fighting each other(tried this out anyways just to see, and it doesn't work except at idle). I run the condenser like I posted with a .072 orifice in the front, a genuine AC DELCO TXV for the rear from a 96-99 BURB, and a GPD compressor, and I have NO problems keeping the inside of the truck COLD! I have yet to find somebody I can't freeze out with the front on fan 2, rear on fan 1, outside air running down the road at 60-70, with both set to max cold. I get moisture collecting on my vents and glass in hot summer weather from the 30 something degree air coming out of the vents. Maybe I'm lucky as I know alot of guys say there A/C is margianal, but mine is friggen COLD! I know mine used to be colder when I had the SANDEN compressor on it, but the crank seal in it went out after 2 years so I switched to a GPD. It doesn't et as cold at idle, but is alot quieter, and gets as cold or colder running down the road as it doesn't cycle as often as the SANDEN did.
 
After being convinced by a savvy salesman to buying a smaller condenser “because it was billed as more efficient” than the bigger one that came from the factory on the Burb I find other 35% BIGGER, better and more efficient condenser than the smaller condenser I have now on my Bur is available.

I was checking out the condenser APDI/PRO # 7014544 FERM mentioned recently in a performance thread being a great deal and big measuring 29 1/8th” wide by 15 3/8th” equating to about 447 +- square inches frontal area and about 6.40% larger than what I have now. As I’m on Rock Auto web site checking out FERM recommendation I find an even BIGGER same styled condenser 4 SEASONS # 40018 made for the 1999 C/K3500 6.5td cab chassis ‘new body style’ w/dual ac ambulance package measuring a massive 35.80” wide by 17.37” tall equating to about 621.8 +- square inches frontal or roughly 30% +- bigger than the one FERM suggested and about the same frontal size as the Burb’s big radiator core which IMHO will complement the Ram Cummins CAC/IC I’m installing.

Round or extruded tubes or plates can be found on these condensers and the extruded types vary in size internally from micro to mini-micro passages which are not interchangeable with the factory tube configuration. These micro and mini-micro extruded tubes get clogged real easy this places an even higher demand for a really pulled down clean and properly working system so additional inline filtration is a must IMHO.

R134a is corrosive when moisture/air enters into the picture so I have switched to Industrial Blend Enviro-Safe R134a substitute which is not corrosive period and use this now for many years with no issues whatsoever. While the debate is ongoing about the fire dangers of carbon based refrigerants they have been around since before those planet killer R12/R134a even existed and R600a/R290 are used exclusively in automotive HVAC in most countries down under it’s very popular too.

Problem with using the biggest condenser is that it uses block type fittings (aka: peanut fittings) that are common on 2001 and newer vehicles and I can’t find adapters or just the male ends to convert my threaded system to this newer style fitting maybe a pick & pull yard will have what I need, or I’ll buy a new hose w/those ends to cut up to adapt this BIG condenser to my system.

My RPO codes for the dual HVAC are C60 & C69.

For many years now I could not find replacement compressor manifold w/hoses for the dual ac in my burb so it was cut and repair as needed and now I find the same setup is used on the 1999 C/K3500 6.5td cab chassis dual HVAC ambulance package and is available from Rock Auto that’s good news.

I like the idea of dual accumulators one for the front and one for the back.

Thought’s and feedback wanted!
 
No, you DO NOT run a TXV on a dual air system for the front, you only run an orifice in the front and a TXV for the rear. And cutting the box to access the rear TXV is the reccomended method by GM due to the problem of the rear lines seizing to the fittings underneath the rear HVAC. In a dual system you either run 1 orifice and one TXV, or 2 orifices, but NEVER 2 TXV's as they will end up fighting each other(tried this out anyways just to see, and it doesn't work except at idle). I run the condenser like I posted with a .072 orifice in the front, a genuine AC DELCO TXV for the rear from a 96-99 BURB, and a GPD compressor, and I have NO problems keeping the inside of the truck COLD! I have yet to find somebody I can't freeze out with the front on fan 2, rear on fan 1, outside air running down the road at 60-70, with both set to max cold. I get moisture collecting on my vents and glass in hot summer weather from the 30 something degree air coming out of the vents. Maybe I'm lucky as I know alot of guys say there A/C is margianal, but mine is friggen COLD! I know mine used to be colder when I had the SANDEN compressor on it, but the crank seal in it went out after 2 years so I switched to a GPD. It doesn't et as cold at idle, but is alot quieter, and gets as cold or colder running down the road as it doesn't cycle as often as the SANDEN did.
Thanks FERM great input!
 
You only need 1 accumulator. Also you only need an accumulator for a line with an orifice in it. All that large diamter tubing coming up from the rear air already acts as your accumualtor for the rear, another accumulator could cause issues with oil settling in it and coming out of circulation. As to the different refrigerants, not sure how they would effect seal life in a compressor designed specifically for use with R-134A. I personally don't have any cooling issues with mine since I swapped to the new style condenser. And it isn't neccesarily about the size of the unit, it is how many BTU's of heat it can shed. I know the newer style trucks have what looks to be a much larger condenser in them, but when you factor in the thickness of it, they really don't remove much more BTU's of heat. As to the hose assembly, make sure it has the correct ends on it. The 6.5L BURBS used there own standard thread fittings for the rear A/C lines at the firewall connections where as others used metric. Don't know why GM decided to use the older standard thread fittings for diesels, and upgrade to metric for the gassers, but it is what it is. And if you need A/C fittings of any kind, call MARKS AIR in TAMPA as they build custom AC systems there for semis, tractors, and whatever else you can think of. if they don't have it, chances are they can find it or build it.
 
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