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Discussion Starter #1 (Edited)
AC Installation in a 1974 105 GTV 2000

I am interested in getting people's feed back on this wiring diagram shown below. I am new to auto electrics and I am eager not to muff it. With this caution I provide no guarantee as to the the correctness, functionality or safety of the wiring diagram that I am proposing. Frankly what I have tried to do is possibly more complicated than needed and it does work on the assumption that two fans (pulling on the radiator side and pushing on the condenser side) do not work against one another when both are activated at the same time. That is, I have assumed that two fans are better than one.

I have combined wiring diagrams sourced off this forum and come up with the diagram shown below.

I have also attached the Excel file used to create the diagram in case anyone wanted to modify it and because the picture quality shown below is not good.

View attachment AC GTV Wiring Diagram 26-01-2011.xls

Wiring Diagram.jpg

If I have designed it properly this is how it should work:

1. Radiator fan comes on when temperature reaches 180 degrees; the radiator fan remains on (even when the ignition is off) until a temperature of 175 is reached;

2. If the AC is on when the radiator temperature switch comes on I have allowed the condenser fan to come on also under the assumption that if the AC is on then the engine is under even greater load and may require a little more assistance getting the temp down;

3. Radiator and condenser fan comes on when activated by a manual override switch which again is not powered by an ignition source with the result that the radiator and condenser fan remains on even when the ignition is off. Note that each power supply (#30) can have a different source, e.g., one from the ignition and the other from the battery for example - it's up to you;

4. Radiator fan and the condenser fan turn on when triggered by the AC trinary safety switch. Note that the condenser fan and the radiator fan are powered from the battery such that both fans may remain on after the ignition is turned off - this may be over kill and either one or both fans could be powered from an ignition source;

5. I have wired the compressor to a relay but I am unsure if this is necessary as all that the wire to the compressor is going to do is turn the clutch on or off. I will need to do some research to see how many amps the compressor pulls;

6. The high speed setting of the blower is connected to a relay although the low and medium settings (which require the use of a resistor) are not.

7. The blower motor resistor contains 4 resistors and will be custom made - because I can't find one and some of the ones advertised on places like ebay cost too much. The low setting on the blower switch has 0.15 + 0.10 + 0.15 + 0.10 (0.50 ohms of resistance), while the medium setting has 0.15 + 0.10 (25 ohms of resistance). Each resistor is rated at 50W. These are ARCOL resistors (part # HS50 0R15 and HS50 0R10). By connecting these resistors in series heat build up is dissipated over 2 to 4 resistors. It's also slightly cheaper doing it this way. As an extra safety measure, a 128 degree Celsius thermal fuse is incorporated after the final resistor also (over kill?). Note that I haven't built this resistor yet so I can't be sure that the resistance levels are right for my fan yet. A pulse width modulation fan would be so much more efficient but for the moment I'll save a little money and use a resistor and as my evaporator box is already installed, pulling it out now is way too much of a hassle.

8. Notice that I have included an AC ON/OFF switch - this was not included in the original evaporator box. This switch allows the blower to be turned on with the AC not being activated, these two circuits are now isolated. This extra function may be useful on a very hot day when the you don't wont to use the AC for whatever reason., e.g., you are wanting to save on fuel or if the compressor is malfunctioning etc.

One unusual thing about the original evaporator box for this model (which I am using) is that is has a defrost lamp on the front of the box. This is odd since defrost only relates to having the heater tap open and the AC on but there is not electrical means of knowing that the tap is open. Perhaps this lamp was only to indicate the the AC and the blower were both turned on.

I am very interested in hearing people's thoughts on what I have put together?
 
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