oldmanyoung

My A/C is blowing a little less cold than it had previously. Not warm, but not ice cold. Suspected it needed a recharge, since it was not a daily driver for awhile prior to me owning it, so I grabbed a can of refrigerant with UV dye and a UV detector kit, but was surprised to find that the pressure was fine (40PSI). I live in Southern California, so it may just be that it’s doing its best in the conditions. Should I leave it at that, or keep looking for an issue?

Rambler65

You don't say the year so the assumption is that it's an R134a system. What is the high side pressure? Ambient temperature? Without knowing the pressure on both sides and checking against what it should be you can't really tell what's going on. How about your blend door, is it working properly? Even if your AC system is otherwise working properly you'll feel warmer air if the blend door is letting some in.

Here is the temperature/pressure and diagnostic chart from the 1999 XJ factory service manual, should be similar for any R134a AC system that does not have a variable-displacement compressor:

oldmanyoung

Thanks. This is all above my knowledge level. Never heard the phrase “blend door”. It's a 2000 4.0. I started noticing the air warming, and a couple times noticed my idle surging with A/C on, so I assumed it was low on refrigerant and short-cycling the compressor. I tested low pressure side with the intention of filling it with UV-dyed refrigerant and finding the leak. When I saw that pressure was not low, that plan was ceased. I will probably just take it somewhere for a look. Thanks again for that very detailed info.

Rambler65

The blend door controls outlet air temperature by mixing air from the AC system (or outside air if AC is off) and the heater. When you adjust the temperature control to be warmer the blend door moves and mixes in more air from the heater core. It can get out of adjustment or stick. So it is possible for your air conditioner to be otherwise working OK but you'll feel warm air.

Another possible problem area to check could be the condenser fan. That fan went bad on my daily driver and since then when the weather gets really hot the AC is marginal especially in stop-and-go traffic.

Maybe pick up one of those thermometers that you can stick in the air outlet? That'll give you an idea if your AC is performing to factory specifications. For example, in 100 degree weather (it was all too near that today!) the factory chart says center outlet temperature should be from 43 to 55 degrees. The upper end of that range is not really going to feel ice cold but should still keep you comfortable.

Aside from that, to really see what's going on in your air conditioner you need a full gauge set, which can then be used to check both high and low pressures to let you know what's going on. (You can find gauge sets for under $50. Some parts stores may loan them out. Those cheap low-side gauges on refill cans are pretty worthless.) It's not rocket science by any means but it is a bit different than the usual wrenching on mechanical parts. There are lots of videos on youtube showing how to work on air conditioning systems.

If you don't feel comfortable working on this stuff obviously you can take it somewhere, but AC work at a shop tends to be very expensive. You'll save a ton of money if you can work on it yourself, but you need to take things slow and not get ahead of yourself.

One thing to bear in mind that's important is if you do have a leak is not to be tempted to put sealer in your air conditioner. Sealers cause all kind of problems and can even ruin shop equipment. Another in the event you work on AC on other vehicles in the future is if you have a variable-displacement compressor you cannot diagnose the system by pressure. The compressor in those systems will keep the pressure up even if the refrigerant level is low. (Fortunately the XJ does not have that type of compressor.)

ajpulley

As mentioned above, do NOT use products with sealants in the refrigerant charge. I also agree that you need a set of gauges to see the low and high side pressures accurately at a given ambient tempurature.

Assuming your electric fan IS working in unison with your compressor cycling, clean your condenser coil. Use a solution of Simple Green and a garden sprayer to soak the condenser and the radiator. After 10 minutes, thoroughly rinse it with a garden hose. Do NOT use a pressure washer. This is inexpensive maintenance you can do yourself.

oldmanyoung

So I’ve been busy, but finally got around to renting out the full gauge set to test high and low side. Here are the readings I got at full blast/fan settings:

Ambient temp outside: 100 deg F
Low pressure side: 40 PSI
High pressure side: 281 PSI

According to the specs listed in a post above this, my low pressure side does seem a few PSI shy of the low end of acceptable, but I don’t know how much tolerance there is for that.

For what it’s worth, I’m able to see that the blend door actuator motor is in fact working. I also removed it, put my fingers on the actual shaft of the blend door and it rotates freely. Where do I look next?

4.3L XJ

Does your system have a thermal expansion valve? (TXV) It is a big brass block that both lines go into and has a little hat on top

oldmanyoung

Not that I can see at a glance. Where would it sit under the hood?

4.3L XJ

Right against the firewall