68 Eldorado A/C relay switch

[Forgiven1989]

The compressor on my 68 Eldorado didn't turn on today.  It worked fine last year.  I wonder if it could be the A/C relay?  Also does anyone know where it is located on the Eldorado?  I think it is on the firewall right behind the engine.  Thanks.

["Cadillac Kid" Greg Surfas 15364]

Dave,
Does the fan work when you turn the selector lever to 1. High, 2.Defrost, 3. Automatic?
Greg Surfas

[Forgiven1989]

Greg,  The fan works in all modes.

["Cadillac Kid" Greg Surfas 15364]

Dave,
If the fan works (and nothing has been changed since the system worked correctly) I would check the connection at the compressor clutch.  Check the positive side for power and check to see that the ground wire has not come loose somewhere.
If there is no power to the posit5ive side of the connector, check the thermal limiter  (it is called a switch, but it is a one time opening fuse) located on the engine side of the heater air box on the passenger side of the car. IF the system was short of refrigerant, the compressor mounted switch grounds the circuit, causing the slow blow fuse to heat up and open the compressor circuit, saving the compressor from undue abuse while the refrigerant (and presumably the oil level) is low.
Greg Surfas

[Forgiven1989]

Thanks Greg I will try that.  Dave

[cadillactim]

The thermal limiter switch didn't start until 1972.  The compressor switch may be bad. The switch prevents the compressor from engaging if outside temperature is below freezing. 

Tim

[Forgiven1989]

Tim, Do you know where the compressor switch is located?  Thanks.

[cadillactim]

It's on the cowl under the hood on the passenger side. The compressor switch and ambient sensor are one unit.

Tim

["Cadillac Kid" Greg Surfas 15364]

Dave,
I just noticed where you are located.  The compressor lock out switch is located in the outside air duct and senses outside temperature. When the outdoor temperature drops to (about) 32 degrees F, the contacts on the switch open and keep the compressor from running.  If the car is outside and it is that cold, perhaps the switch is functioning corectly.
Once you find the switch (and ambient sensor) you will notice there are two pairs of spade connectors.  If you have an ohm meter, with the plug from the system disconnected, check the resistance between the two connectors of each pair.  The compressor lockout will either be 0 resistance or an open circuit as indicated by a reading of "infinity".
Depending upon the ambient temperature the other pair will show a resistance that varies with temperature. 
Greg Surfas

[Forgiven1989]

Thanks a lot guys.  I'll look for the switch today.  Dave