Thanks so much for the efforts here on the forum. I am a new member, sorry this is a long post but I wanted to be thorough explaining the issues and efforts so far, before asking for help.
I'm helping a friend with his Jeep WJ, 1999 Grand Cherokee 4.7, having insufficient A/C cooling.
The JGC Limited has dual temperature controls and hence dual blend doors. We carved into the plenum behind the glove box and determined both blend door motor drive cogs were stripped. We replaced the blend doors with an aftermarket blend door pair, which is fixed to both flaps, hence the firewall side motor and passenger control are now null. Both blend doors follow the driver's setting. It seemed to work fine mechanically reaching both plenum blocking positions when we were done, closed up the plenums and re-sealed it.
Blend door fix improved cooling some, but not substantially. (more on this below)
We verified all temperature sensors measured and tested within spec for resistance and appear to be working as do the A/C high and low side cut out switches.
We recovered the freon for leak test = 30 minutes holding with no loss at 29.x inches vacuum = Pass. We then continued evacuation for 1 hour to pull any moisture. No signs of desicant contamination during seals replacements and Shrader service we could see, no prior damage to A/C compressor. New Schraders high and low side both with pressure seal caps.
The sticker on the hood called for 24 ounces of R134a which we provided by low side input, via standard gauge manifold set.
During fill, the compressor cycled on and off as the pressures climbed and then went to full time on, (stopped cycling).
We powered down the system and verified we equalized within less than 5 minutes.
At 85 degree outside ambient, 65% relative humidity, near sea level we got the following pressures...
At 700 RPM idle, 43 PSI Low side, 215 High side, 17 degree delta from center louvers panel mode versus outside ambient. The pressures seemed a bit low within spec, but having put the charge in to spec by weight we started looking elsewhere.
With compressor disconnected, system on full demand, we measured temperatures at the louvers to be heating above outside ambient. This called to question new blend door failures, dirty evap or engine compartment hot air getting in past leuvers.
We blocked off the fresh air intake in the cowling above the firewall, set to recirculate max air, considering engine. It helped some, but still no better than 15-17 delta panel louver versus outside ambient.
We then blocked off the hot water inlet to the heat exchanger which did bring the panel louver temps back to outside ambient with compressor disconnected but AGAIN no major benefit to the cooling delta panel versus outside ambient.
We then added 4 more ounces of freon just to read comparison. Pressures rose to 46 psi low side, 230 psi high side at idle, again little benefit to cooling at all. We then ran a road test and noted at 1800 RPM we were seeing 35 PSI low side, 275 high side, after surging to 30 psi / 350 psi briefly before stabilizing back to 35 / 275 at 1800 rpm, 85 degree outside ambient.
We then recovered the added freon back to prior pressure values, to protect the system from over-pressure.
This seems to suggest low on low side, high on high side and makes me suspect the orifice tube is partly blocked even though it equalized appropriately on shut down, 5 minutes to balance fully. No hissing, no squealing, no compressor noises.
At 85 outdoor ambient 65% Rel. Hum. the cabin temperature in the vehicle barely comes below 75 degrees, even with max / re-circulation and full time compressor on.
We have replaced the viscous fan clutch drive new and confirm the solid state relay driving the secondary electric fan is functioning properly as does the fan when called on. Engine operating temperatures are nominal and well behaved. The condensor is in good shape and the stock radiator is 4 years old. Vehicle has been well maintained overall, 3rd owner.
We're intending to ...
1) replace the orifice tube line (integral assembly) if only to assure new component. (pull front clip, uggh).
2) re-open the plenum behind the glove box and verify the blend doors are still sealing to insure all the blower flow is crossing the evap. and not diverting around through the heating plenum.
3) learn if the compressor should cycle under normal conditions or is full time compressor expected on 85-95 degrees outside ambient?
I'd like to ask if I've overlooked anything or missed on diagnostics ? I'm not an A/C expert but have worked on many systems. Seems to me if the compressor can hit 350 psi on surge, the compressor is capable of adequate compression. We're hoping this isn't indicating a dirty blocked up / fouled evaporator considering none of these WJ series ever came with a serviceable screen to keep the incoming air clean.
Thank you again for any suggestions.
Urbansound = Mike, Holland, MI