I don't know if this idea is worth pursuing but I would like to have a blinking LED to remind me to pull the choke off when the car is warmed up. For those who have worked with electronic circuits (I gather some here have) what is the easiest way to do this? I was thinking about connecting an op amp up as a comparator with one input going to the thermostat and the other input wire going to an adjustable resistor so that when a certain resistance is reached the LED that is one of those blinking types is turned on. Where can the LED be hidden so it can't normally be seen? I would assume a switch connected to the choke control would be needed to turn off power to the op amp to stop the LED from blinking when the choke is pulled off. Is there an easier way?

Now if I could just edit the word remonder to read reminder.

Edited July 2, 201311 yr by Mikes Z car

Buy an "sand through the hour glass" style egg timer. Put velcro on both ends. Stick to dash on top of tach area. When you start your car and put the choke on, turn it over and stick other end to the dash. When the sand runs out, push your choke off.

The low tech approach. Will last forever too.

As an interesting project, your idea to create a smarter choke light is great. Nothing worse (well, a few things...) than leaving your choke on too long. Wastes fuel, clogs up plugs, chokes small chidren on the sidewalks with the black cloud. But there are some places where computers don't belong. Coffee pots and Datsun's are just two...

You may be overthinking this. Rather than hiding the LED, put it readily in view. You should be able to get a blinking LED at Radio Shack. Use a switch that opens when the choke is off.

Since the choke is only needed for a few seconds to a few minutes, a flashing reminder that its still on should be all you need.

I am working on a different problem. My VintageAir uses R134 and is quite capable of freezing up in humid Florida air. I'm looking for a precision sensor that will interrupt the compressor signal when the air coming off the evaporator drops down to 36 degrees.

DJ, The internal control your knob or slider is attached to, IS the temperature sensitive switch you are looking for.

Vintage air warns of this freeze condition, and it just means your dash control thermostat is just set too cold (and your system is working too efficiently!).

Just turn the "cool" knob or slider to the warmest (least cool) temp you need to get the cooling you desire. Too cold a setting will freeze the thing solid as you have discovered. Takes a bit of trial and error to get it right. Not exactly a hi-tech system.

DJ, The internal control your knob or slider is attached to, IS the temperature sensitive switch you are looking for.

Vintage air warns of this freeze condition, and it just means your dash control thermostat is just set too cold (and your system is working too efficiently!).

Just turn the "cool" knob or slider to the warmest (least cool) temp you need to get the cooling you desire. Too cold a setting will freeze the thing solid as you have discovered. Takes a bit of trial and error to get it right. Not exactly a hi-tech system.

zKars, understood. In Florida, humidity varies widely both from day to day and throughout the day. It is possible to set the temperature knob when you get into a hot car per the instructions. Later, after the car cools and you turn the fan down, I've found the coils can start to ice up before you realize. Once the coils begin to ice up, air flow drops and the temperature probe sees even less cold air. This causes the compressor to run longer and icing builds up rapidly.

And as per the VintageAir instructions, the only solution is to turn off the AC until the ice melts.

What I am looking for is a probe in contact with the coil itself. Once the coil reaches 34 degrees, the sensor opens a relay to cut off the compressor and lights an LED to alert you to the fact that the temperature control is set too low.