I had the exact problem with my A/C system. mark canning sent me this info. to check the system, most probably the relay on top of the A/C box under the hood. He is right that only a 69 relay will work, take your old relay in the store with you, DONT accept any different tab alignment on the new one, it MUST match up the same or it wont work right.
good luck and keep the beaches warm there when I visit Destin this winter.
From Mark Canning checking A/C elec. system:
"With the key on and the fan switch in high. Unplug the 4 wire connector from the fan relay on the top of the evaporator box in the engine compartment. Check for voltage at the 12 gauge (thickest) orange terminal. If good your getting 12V from the battery, if not your fuse or fuse holder is bad.
Check for voltage at the 18 gauge(smaller) orange terminal. If your not getting 12V then you have a problem with your fan switch on the dash, or the wiring between the switch and this connector. If you are getting 12V (at both orange wires) then the relay is probably bad. Read below on buying the right relay.
The relay coil is picked up by 12V between the 18 gauge orange and 12 gauge black wires.
This closes a contact between the 12 gauge orange and 12 gauge purple wires. 12 Volts
(some amount of current really) flows from the battery, through the fuse, through the
contact, to a terminal on the blower motor resistor, and on to the fan motor.
Plug everything back together and toggle the switch in and out of high. If you can't hear the relay clicking when you put the switch in high, it's dead. The two prong connector on the other side of the evaporator is the low temperature cut off switch. It will open if the air temperature gets down to 29 degrees or so and cuts off power to the compressor clutch. It keeps the evaporator from freezing up. Doesn't have anything to do with the blower circuit.
Check to see if the contact is stuck shut. Check the resistance on the relay for the terminals that connect to the #12 AWG orange wire and the purple wire. With the relay deenergized there should be infinite resistance (open circuit) Check the resistance between the #18 AWG and the Black #12 wire, should have some resistance, maybe 100 to 200 ohms indicating the coil is intact. Make sure you have 0 volts on the small 18 gauge wire with the key off, or with the key on and the switch in any position BUT high. This wire should only have 12 volts with the key on AND the switch in high.
Make sure you have a 69 relay as they are different than the 68 relay. 69 relay has a T
shaped connector with two terminals next to each other, and two more vertical below these
two. You can't put a 68 relay on a 69 connector, though so that shouldn't be an issue.
If it's stuck you may be able to free it up by rapping it on a hard surface. Give it a couple of good shots onto a piece of wood or something similar. Don't ding it up though cause if it is bad and you bang it up you won't be able to return it."
69RS 350/255 LM1, Balanced, TRW forged pistons, .30 over, TH-350 auto.,
Dover White,Blue Vinyl top, F&R spoilers,pdb, close ratio ps,am/fm,3.08 Posi., A/C, fold down rear seat
My RS www.brainerd.net/~knudsen/69RS