A/C question

I've posted something similar before, but....On my 99 I only have trouble when it's hot and humid outside. I work perfectly when the humidity isn't high or it isn't your Summertime VA/NC temperature. Without fail, I'll have warm air and the distinct smell of a frozen A/C system. If I cut it off for about 10 minutes, I'm fine until it does it again. I replaced the low pressure switch on top of the accumulator a week ago and still have the same problem. The dealership says that my refrigerant may be low and they want to drain the system, and refill it. They want to check it by weight. Think that's a good idea?

It sounds like the system is low. I would stay away from the dealer. You have a few options. Walmart and /or auto parts stores sell a charge kit . Harbor Freight sells an a/c gauge kit then you buy the cans and the valve for the cans. The charge kit will be the cheapest way to go. Just follow the instructions . Make sure you have good air flow through your radiator and condensor .Good Luck

You can get a pretty good idea of what the system is doing by putting your finger on the low side line as close to the firewall as you can get. It should be cold but not icing (maybe slightly frosty). Next try nearer the compressor, if it's very cold your overfilled or the evaporator is iced up.
If it was very low on freon, the low side switch would cycle it off.
The system is easy enough to quick check. Low side pressure should be 25-35, when the outside temperature is 70-80. I usually test with all the doors open and the fan on high.
When the evaporator starts icing, the cold (heat exchange) often travels down the low side tubing towards the compressor or saying it another way, when the evaporator is iced, the freon stays liquid longer and the heat exchange can migrate down the tubing towards the compressor.. When your overfilled the pressure can push the cold (heat exchange) past the evaporator coils and down the tubing.
The earlier models had a thermostat at the evaporator to avoid this, when it iced up, the thermostat would shut it down.
If the drain hose is plugged and the drain pan is full of water, they tend to ice up faster. High fan can also help keep the icing down some.

Did the dealership quote you a price? Call around and get a few quotes. Measuring by weight is the most accurate way to determine the charge. Too bad it has to start from empty. However a decent set of gages, and a thermometer is good enough and no need to evac the system.

When you replaced the switch did you get the "fixed" one. There's a TSB regarding evap freezeup that requires a new (and improved) cut-off switch.

Don't add anything unless you're sure it's low.

When I ordered the switch, I used the number on the TSB that referenced a 99. I feel good that I bought the right thing. The shop quoted me $70 to remove, refill, and check for leaks. i figured I would give them a shot. Think it's to much?

Hot and humid is routine here in Houston. If it is not icing up, icing up should be somewhat obvious as the air flow drops substantially when it does, it could be a vacuum line or vacuum valve failure on the damper door which is spring loaded to switch to fresh, hot humid, outside air if the valve fails to move the damper door to circulate mode on the MAX AC setting. Ive had that problem with both my primary XJs.

8MUD,

So I wonder why they got rid of the evaporator thermostat on the later models?