jordan96xj

I just walked out to the parking lot and ran my AC to double check your observations. If one line going into the firewall is ice cold, and the other is about ambient, then your compressor and refrigerant are doing their job (at least enough to move on to other items).


If the line going to the expansion block/orifice is ice cold, but there is no cold air in the cabin that probably leaves just 2 possibilities. Either air is not moving over the evaporator (I think you are close to having ruled this out), or the expansion valve is not working properly and is not allowing cold refrigerant into the evaporator.

ixanay_on-the_exjay

I am plagued with this same issue, not sure about my fan and pressure since I have not done nearly as much discovery as you. I have short intermittent compressor engagement as well as no cold air... anyway in my research I heard that (could be untrue sorry if so) if your pressure is too high in your system that could also cause this problem... something to maybe look into if you can't locate any leak... I just assume the worst so I figure I have a leak somewhere.

4.3L XJ

Just a comment on line temps. The "hot" side, or condenser should be hot enough it is not comfortable to hold on to it. This is so it can dissipate heat and cool the refrigerant enough so that when it evaporates it can gain heat in the evap coil. If you can hang on to that hot side and it only feels warm, it is undercharged and not in a liquid state in enough of the coil to get rid of its heat. If the cold side is cold, but not pulling moisture out of the atmosphere, it is not cold enough. It should be about 34 - 36°. Lower than that and it will make the coil a block of ice and cease cooling. These are just ball park hot cold gut feeling things that I use to very quickly assess the level of refrigerant in a system. If a unit is cycling on and off quickly, it can be overcharged or have air in it. If you guys have had your lines open at all, and didn't pull a deep vacuum with a dedicated deep vacuum pump for at least 15 minutes, then you need to start over or it will never work right. If you have had leaks at the suction side, you also might have pulled air into your system and it needs to be resealed and pulled down before recharging. Even though we compress air all the time, in a refrigeration system it is considered a non compressible. Meaning you don't have the means to compress it far enough to make a liquid out of it, so it won't let the system operate properly

Alfie9294

My father in law is having similar trouble, gave up on diagnosing it himself and its in the shop atm, ill post any revelations.

Bugout4x4

Lot of good advice here but before you go all out refilling that system have you just tried to put a can in it? All it will cost you is one can of refrigerant if it doesn't work. I have several vehicles that do this exact same thing every year and one can does the job every time.

No matter how good you try to seal A/C systems they still leak over time through the natural molecular porosity of hoses, urethane or silicone O-rings, shaft seals, aluminum, gaskets Etc. Just like tires do even if they have no normal leaks. Most times the compressor shaft shrinking and contracting from winter cold can allow a small amount to leak out the shaft seal through the winter.

There is a "cold spot" that moves along the line from the compressor towards and finally into the evaporator where it belongs as you fill it to the proper point. You might feel the line cold outside going into the firewall but if it's low, that cold spot won't move it's self "inside" to the evaporator where it belongs until it's right.

Bypass the low pressure switch with a paperclip jumper and see if it keeps the compressor engaged continuous. If it does then your pressure switch is working and it is definitely low.

Rambler65

You really need to hook up a full gauge set to see what's going on.

The 1999 XJ shop manual defines excessive compressor cycling as 10 on-off cycles per minute or more. What can typically happen is that due to low refrigerant charge the low side goes into very low pressure (possibly even suction) when the compressor runs for a few seconds, triggering the low pressure cutoff switch and disengaging the compressor. Then the low side pressure rises to the point where the switch allows the compressor to run again. This continues and you get the rapid cycling effect.