Anyone Running An "Old Air" A/C Unit?

[69sixpackbee]

If so, how much 134 did yours require? The sheet they sent me says 26 oz. This does not sound right.
Thanx!

[Frank_Zeller]

I put in about 30 oz. 2 and a half cans R134.

[69sixpackbee]

How well does it work?

[Frank_Zeller]

Well after much tinkering I would put it up against a perfect condition original AC system.................took a lot to get it there. Found out the two main problems were the mechanical AC compressor cycle switch and air leaks around the windows.

Also

The condenser is too large for the evaporator causing the system to be super-efficient which results in evaporator freeze over, especially on the highway. Couple that with that slow responding mechanical AC compressor temp cycle switch and the system did not work very well.


Things I did to get the system dialed in:

Had to add more insulation to the firewall and front floor pan.

Had to silicon up the vent windows and fix the leak around the door window.

Built an adjustable electronic AC compressor cycle switch (with help from the guys at work) that has only 1 degree of variance. The mechanical one was 5 degrees. So now the compressor is on for about 20 seconds off for 10. This allows me to keep the evaporator just above freezing, but still have constant 36-degree air vs 38 to 42 vent air mechanical switch.

Put foam filler panels around the condenser so that all the air would have to pass though it. So got rid of all the gaps.

I have only one rap of the black insulating tape around the since tube for the expansion valve. This mod helps keep the evaporator from getting to cold. Ran around with no insulation for a while, but would only get a 40 degree vent temp

[guypm]

Frank_Zeller,
What kind of radiator fan are you running ? I have yet to charge my old air system. I bought the old air kit that comes with the bigger condensor, a new evaporator and the poa valve delete tube. It also came with a pressure switch. The folks at old air told me that i would have to run a electric fan or the unit would not cool efficiently. They said that it would get too high of a head pressure too quickly. Mine is in the paint shop at the present so im not able to finish the ac at this time. I'm thinking of using "Autofreeze" coolant when the time comes. Do you know where i might get one of those cycling switches you made ? Any info would be appreciated.
Thanks, Guy

[Frank_Zeller]

Running a 19.5 inch 7 blade fan from a 1969 Pontiac Firebird 400 with AC. Using a 1985 GM truck fan clutch. Working on making the temperature cycle switch. Instead of buying the electric fans I put foam around the condenser so all the air the fan sucked would have to pass though it first. No problem with high head pressure.

[69 1/2 Sixpack Bee]

Thanx!!

[guypm]

Thanks Frank,
Your info was very helpful.
Guy

[Frank_Zeller]

My intial plan was to go out to the junk yard and get a AC temp cycle switch setup from a Toyota.

[crew70]

I am going to need this info later
thanks

[nosto]

Great timing! I just finished my Old Air install last week (except for charging). This info will be a real help when I actually get on the road!

I did the insulation and have new door rubber, but the foam and single wrap trick is good info.

Any chance of getting the plans/schmatics for the electronic temp control? Some of us (me) are just too lazy to design their own.

Thanks,

[69sixpackbee]

Heres a simple switch that I found on the web. It looks like what we need!

Electronic Thermostat and Relay Circuit

Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater (or A/C with a different temperature thermister) through the relay contacts. The relay contacts should be rated above the current requirements for the heater.

Temperature changes are detected by a (1.7K @ 70F) thermistor placed in series with a 5K potentiometer which produces about 50 millivolts per degree F at the input of the LM339 voltage comparator. The two 1K resistors connected to pin 7 set the reference voltage at half the supply voltage and the hysteresis range to about 3 degrees or 150 millivolts. The hysteresis range (temperature range where the relay engages and disengages) can be adjusted with the 10K resistor between pins 1 and 7. A higher value will narrow the range.

In operation, the series resistor is adjusted so that the relay just toggles off at the desired temperature. A three degree drop in temperature should cause the relay to toggle back on and remain on until the temperature again rises to the preset level. The relay action can be reversed so it toggles off at the lower end of the range by reversing the locations of the 5K potentiometer and thermistor. The 5.1 volt zener diode regulates the circuit voltage so that small changes in the 12 volt supply will not effect operation. The voltage across the thermistor should be half the supply or about 2.6 volts when the temperature is within the 3 degree range set by the potentiometer. Most any thermistor can be used, but the resistance should be above 1K ohm at the temperature of interest. The series resistor selected should be about twice the resistance of the thermistor so the adjustment ends up near the center of the controlhttp://www.imagestation.com/picture/...9.gif.orig.gif

[Frank_Zeller]

Bud,

Consider adding a voltage regulator to improve the accuracy as the load changes on the electrical system. Also add an LED to show when the relay is latched. You can play with the mass of the thermistor to fine tune the response of the switch.