Automotive Air Conditioning Information Forum (Archives)

johnp on Thu May 29, 2014 9:21 PM

Year: 1994
Make: GMC
Model: Suburban
Engine Size: 5.7
Refrigerant Type: R-134a
Ambient Temp: 85
Pressure Low: 42
Pressure High: 200
Country of Origin: United States

First of all, thanks to anyone who can help!

The vehicle is a 1994 GMC Suburban w/rear air, 4lbs. capacity R-134a. It's my FIL's van. He said it wasn't cooling good enough, so he added 'a couple cans' to it. Not knowing how much was in it or how much he added, I had the system evacuated. I then pulled a vacuum on it, and filled the system with 4lbs. After it was fully charged, I let the van run about 15 minutes at 2000 rpm and took my gauge readings.

2000 rpm, ambient temp 85F:
Low side - 42psi
High side - 200psi
Vent temp - 57F front, 67F rear

Hmm, not what I was expecting, but I take it for a drive anyways. Within 5 minutes of driving, vent temps are 53 for the front, and 56 for the rear. So I head back home, and let the van idle for about 10 minutes and check gauge readings and vent temps again.

At idle, ambient temp still 85F:
Low side - 67 psi
High side -180 psi

Then, I turn the rear a/c off and let it stabilize for about 5-7 minutes and start getting a little more thorough, checking evap and condensor temps.
Low side - 63 psi
High side - 165 psi
Evap inlet - 65.5 F
Evap outlet - 65 F
Condenser inlet - 120 F
Condenser outlet - 110 F
Vent temp - 70.5 F

After this I brought the van back up to 2000 rpm and let it stabilize for 10 minutes, then sprayed the condenser with cold water. Pressure and temperature follows.

Low side - 53 psi
High side - 150 psi
Vent temp - 55 F

Now, throughout all this, I noticed my high side was fluctuating slightly, really more of a vibration. I went to my neighbor's to borrow his gauges to see if it was present on his too, just to be sure, and it was. It wasn't much, less than 5 psi at idle, a hair over 5 at 2000 rpm. That's where I stopped and came here to post. Before I continued troubleshooting, I wanted to know if that little fluctuation would be compressor related, or with it being so small, is it acceptable?

Anything else stick out? I have some thoughts, considering who knows what he or the previous owner did to the system, but there are a lot of people here who really know their stuff so I'd like other opinions.

BTW, all gauge readings are with Mastercool gauges and temp readings are with a Fluke thermocouple.

GM Tech on Thu May 29, 2014 10:04 PM

Suction is too high- could be stuck open rear TXV- did it ever get the service bulletin fix? - you can try to see by using a heater hose pinch clamp to completely block the return flow from the rear- at the rubber hose under the rear evap. If suction drops to about 25, then your cooling will begin-

Look up the '94 TSB for the rear unit...

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Jag987 on Fri May 30, 2014 12:10 PM

That is what amazes me about this site. Someone remembers a tsb about a 20 year old vehicle.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Dougflas on Fri May 30, 2014 1:29 PM

Quote
Originally posted by: Jag987
That is what amazes me about this site. Someone remembers a tsb about a 20 year old vehicle.

How about posting the TSB so we can all see it?

GM Tech on Fri May 30, 2014 11:00 PM

LOUD KNOCK FROM A/C COMPRESSOR #56-12-01
SUBJECT: LOUD KNOCK FROM A/C COMPRESSOR (REPLACE COMPRESSOR AND THERMAL EXPANSION VALVE)
MODELS: 1994-95 CHEVROLET AND GMC C/K MODELS WITH REAR A/C (RPO C69) OR REAR HEATER AND A/C (RPOS C36,C69) BUILT BEFORE THE FOLLOWING VIN BREAKPOINTS:
DIVISION VIN CHEVROLET SJ300349 GMC TRUCK SJ701253
CONDITION:
SOME OWNER'S OF THE ABOVE LISTED VEHICLES MAY COMMENT THAT THE A/C COMPRESSOR HAS DEVELOPED A LOUD KNOCKING NOISE. THE A/C SYSTEM WILL CONTINUE TO COOL.
CAUSE:
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 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.
CORRECTION:
REPLACE THE A/C COMPRESSOR, THE THERMAL EXPANSION VALVE (TXV), AND ADD AN IN-LINE FILTER.
SERVICE PROCEDURE
1. RECOVER THE R-134A REFRIGERANT CHARGE (SECTION 1-B OF SERVICE MANUAL). 2. REPLACE THE COMPRESSOR AND BALANCE THE PAG LUBRICANT IN THE SYSTEM FOLLOWING THE PROCEDURES IN THE VEHICLE SERVICE MANUAL. 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 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. 11. LIFT THE RIGHT SIDE LOWER TRIM PANEL AND ROLL FORWARD TO REMOVE, THIS EXPOSES THE REAR HVAC EVAPORATOR CASE MODULE. 12. USING TEMPLATE (FIG. 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. (FIG. 1). 13. USING TEMPLATE (FIG. 5), MARK CUTTING LINES ON THE LOWER EVAPORATOR CASE USING A CHINA MARKER OR EQUIVALENT. (FIG. 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 (FIG. 1). DO NOT CUT REAR EDGE OF EITHER ACCESS DOOR (FIG. 4 AND 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 (FIG. 2, VIEW 1). DO NOT USE A LARGER DIAMETER CUTTING WHEEL.
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 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 (FIG. 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" CROWS 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 N.M 14-25 LB.FT. OUTLET 15-22 N.M 11-16 LB.FT. 19. PULL BACK ACCESS DOOR ON THE UPPER EVAPORATOR CASE CAREFULLY TO PREVENT BREAKING THE CASE (FIG. 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 (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 (FIG. 3, SECTION 1-1).
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.
PARTS INFORMATION
P/N DESCRIPTION QTY 52450767 OR 52470592 FILTER 1 1134328 COMPRESSOR 1 52469382 THERMAL EXPANSION VALVE 1 3096068 ORIFICE TUBE 1
PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.
WARRANTY INFORMATION
FOR VEHICLES REPAIRED UNDER WARRANTY, USE:
LABOR OP DESCRIPTION LABOR TIME USE PUBLISHED D4440 COMPRESSOR ASSEMBLY-REPLACE LABOR OPERATION TIME
D3220 VALVE, EXPANSION-REPLACE 1.7 HRS.
FIGURES: 5
CAPTIONS: FIGURE 1 - EVAPORATOR CASE MODULE, TEMPLATE PLACEMENT 1. UPPER EVAPORATOR CASE 3. UPPER TEMPLATE PLACEMENT 2. LOWER EVAPORATOR CASE 4. LOWER TEMPLATE PLACEMENT
FIGURE 2 - ACCESS TO TXV AND CAPILLARY HOLDING CLAMP 1. TXV 3. HOLDING CLAMP 2. A/C TUBE 4. CASE WALL
FIGURE 3 - PLACEMENT OF HOLDING CLAMPS 1. A/C TUBE 4. SECONDARY HOLDING CLAMP 2. CAPILLARY CRIMP 5. CAPILLARY TUBE 3. PRIMARY HOLDING CLAMP 6. TXV
FIGURE 4 - UPPER EVAPORATOR CASE TEMPLATE
FIGURE 5 - LOWER EVAPORATOR CASE TEMPLATE
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.
COPYRIGHT 1995 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.
© Copyright General Motors Corporation


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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cussboy on Sat May 31, 2014 1:15 PM

Mrs. Cusser had this same vehicle; AC worked good before the R4 compressor leaked every few years.

johnp on Sat May 31, 2014 5:56 PM

Thanks for the suggestions, I did not know about the TSB. I seriously doubt the PO ever had it fixed. I won't be able to get to the Suburban until Monday, so I'll try pinching off the return then. If I have to replace the TXV, I'm going to go ahead and replace the rear evap too. The rear TXV being stuck open makes perfect sense, I knew I was overlooking something simpler once I noticed the gauge flutter. It never hurts to have more than one set of eyes on a problem though!

I'll let you all know what I find...

johnp on Wed June 04, 2014 11:54 PM

I wanted to provide an update.....

I checked the TXV, it had not had the TSB fix. While I had the box open, I went ahead and replaced the TXV and wrapped it up properly. I decided to replace the OT while I had the system open, besides, I wanted to check its condition anyways. I'll talk more about the OT in a minute.

I recharged the system to spec, ambient temp 95F. Low side 30, high side 225. Front fan at med/low, rear at med. That's where I was getting the best cooling. Both front and rear vent temps 55-57. Unless there's something simple I'm missing, I'm done working on the 'Burb. Here's why.

The previous owner (before my FIL bought it, obviously) took it to a 'mechanic' several times for different things, one of which was A/C work. Let's just say I know how this 'mechanic' works, and how he hacks anything he touches. Here's a list of things he's done, some of which could be the problem.

Accumulator is for front A/C only. I know this by the size, front only is 8", front and rear is 9". It could have also come from another vehicle (used).

Suction/discharge hose assembly did not have suction fitting. It's also been cut and spliced with hose clamps, probably because it was leaking.

Since the hose assembly did not have a suction fitting, he put a suction fitting on the accumulator....where the LPCO was! I was wondering why I couldn't find it!

As a result of the above line, the compressor clutch has been wired to something (I'm thinking the LPCO connector) so that it will turn on and off with the button.

The rear evap is used. As in from another vehicle. From the local junkyard. I know this because it has their unique paint marking. I don't know about you, but I wouldn't use an evap from a system in unknown condition! They don't cost that much new!

One last thing...that I know of. The rear evap under the car (right before it enters the interior) has a fitting where it connects to the TXV. Well apparently, he tried to disconnect here to replace the evap, and ended up twisting the line some. Isn't that nice. Too cheap to replace it I guess, even though he'd charge 4-5x retail to the customer for it...plus labor.

HACK. HACK. HACK. Am I wrong?

Like I said, unless I'm missing something simple, I'm done. With everything I've found, there's no telling what I can't see. I have no idea what else has been hacked, what the front evap looks like, how much oil is in the system, etc. The only thing I do know is there's no sealer in the system. Well, I don't KNOW...but I didn't see any signs of it.

The only thing I can recommend to my FIL is a near total system replacement. He won't go for that. I'm surprised he sprung for the TXV and OT.

Oh, I almost forgot. The OT. Metal shavings. I don't think I need to say anymore.

Any suggestions? Other than TSR? Haha, thanks for the help guys. I'm doing a TSR on my 97 Grand Voyager either this fall or next spring, and I know where I'm buying everything.

Edited: Thu June 05, 2014 at 12:22 AM by johnp

webbch on Thu June 05, 2014 9:11 PM

Well, you could potentially save the compressor by doing a TSR now (didn't see where you mentioned compressor noise, even though the TSB mentions it), but sounds like that's about all. Do the suburbans use an OT in the front and TXV in the rear then?

Can't say I blame you for letting it be for now. Either do it right, or leave it alone.

johnp on Fri June 06, 2014 1:49 PM

Yeah, the Suburbans have an OT in front, TXV rear. The compressor has a slight rattle at 2000rpm and up, but it's really hard to notice unless you're listening for it. I'd love to make everything right on it, but I'd most likely have to foot the bill. Seeing as how it's not mine....not gonna happen. When he gets home we'll see what he says.

I drove it back to his house yesterday, never over 40 mph. Ambient 85-87, front vent got down to 45F. With Houston area humidity (80-90%) I don't think it's that bad. I think if I'd driven longer, it would've come down some more.

BTW, that hack messed with the front evap too. Only 3 screws in it, with silicone gooped all along the seam. At least he managed to get 4 screws in the box in the rear.....

johnp on Fri June 06, 2014 1:53 PM

Quote
Originally posted by: webbch
Can't say I blame you for letting it be for now. Either do it right, or leave it alone.

Exactly. Besides, if I were to replace just one or two things and it quit working again in a few months, guess who gets blamed?