'79 240 D Have replaced air conditioning thermostat. Have thermostat set to where the compressor will engage and will produce cold air but will not cycle. Need instructions on how to fine tune the thermostat so that it will cycle.

What are you calling the air conditioning "thermostat?"

Have a great day,

On the '79 model, 123 body style, the air conditioning thermostat is behind the little knob that is just above the air and heat fan control. It has a gas filled tube, similar to a capillary tube that extends into the evaporator chamber where it picks up and reacts to the air temperature. It controls the temperature of the incomming air into the auto passenger compartment by cycling the compressor. My problem is that I don't know how to fine turn the adjustment so that it will make the compressor cycle. Hope someone can help me. Billmar

Is the system making really cool air? Is the bulb tightly and properly in place? Are you sure there is no short around the switch, like maybe someone jumped a hot wire to the compressor or one of pressure sensors or something?

This is a new one on me. I've done a lot with 123 a/c's both manual and ACC systems, and I've not run across this before.

Did you replace this part in an effort to get the compressor to cycle? The only US car I've had with a system that I think is like yours was my '77 240D and I haven't had it since '85, so I just don't remember for sure. I was thinking that the compressor on this car was cycled by the low pressure switch.

Have you put gauges on to monitor the pressures?

Good luck,

The the thermostat is attached behind the vaccum control that closes and opens the duct doors. The vaccum control developed a leak that had to be fixed and in the process of removing it, I accidently broke the capillary tube off of the original thermostat., which then, had to be replaced. The new part came with instructions to set the fine tuning control so that the compressor would come on when the control switch (dial) is in the 8 o'clock position. I have done all of this per the instructions and the compressor comes on as it should but will not cycle when the set temperature is reached. It will eventually freeze up the condensor . The system was working perfectly before I started the repair. I have had gauges put on the system and it appears that the refridgerant level is correct. Any suggestions will be appreciated. Billmar

Re: Air conditioner thermostat problems. I have just found out that my air conditioner condenser fan switch is bad and am wondering if that might cause the compressor to not cycle properly. Regards Billmar