2002 Wrangler Sport Blowing COLD air.

There are two issues here.
If there is no heat or not hot enough, replace the thermostat and Check the coolant level.
No Air coming out could be either the Blower Motor, The Blower Motor Resistor pack or the switch in the dash. These jeeps are know to burn up the switch and wiring harness when the motor draws too many amps. I just installed all of the above in my 2000 4.0 Sport.

The first thing to do would be go to your local auto parts store and buy an air conditioning recharge kit. Provided your vehicle isn't too old, they sell recharge kits that require no tools.

If their is a leak anywhere while you recharge, you will know.

Try recharging the air conditioning first, it is very simple and the kits come with simple instructions.

If there are no leaks, your A\C will blow cold air again. As for the pressure, if it continues to slightly blow air you may be looking at a new air compressor unit or a vaccum line. A new unit will run you anywhere from $200-$2000 dollars plus labor depending on the vehicle.

If the recharge works, at least you will have slightly blowing cold air rather than hot and you can continue that way until the unit fails.

you need to install gauges and check ac pressures. if pressures are equalized then you have a bad compressor. a simple test is to make sure compressor is running and check to see if the drier is cold, it should be very cold and sweating.

Heater blowing cold air,indicates towards low or no coolant or the coolant flow is getting obstructed or the heater core is clogged or hot to cold moving flap/ door is stuck in cold mode. There are many possibilities, that needs to be checked. Click the link below for step by step details:--- http://technoanswers.blogspot.com/2011/10/heater-blows-only-cold-air.html ---------- This should help.Thanks.Helpmech.

chek that the front fan is blowing when the AC is turned on

it probably just needs recharged you can get cans at walmart for them

Heater blowing cold air until I get on the interstate, then it works; however, when I stop at lights it starts blowing cold air again. The temperature gauge will be in the middle but the car will still be cold until the car starts moving.

Let it sit for awhile because it takes cold oil a while to leak down to fill everything. Did you get 3.5 quarts of oil out when you drained? Just add as much as you can, wait awhile, check your dipstick, and add more until you can get it all in the fill hole. With a cold engine and cold oil, it takes a little while.

You can usually only get about 18 gallons in a 19 gallon tank and you likely have 4 gallons left in it when the gauge reads empty

This may be the AC compressor cycling switch is defective. It is located in the larger of the 2 AC lines coming from the compressor, it has a wire connector to it with 2-3 wires. To verify this is the issue jumper the connector with a small piece of wire and see if the compressor runs.