Air condition problem

[NHbalerman]

Working on the ac on my ford 7740 and when you turn on the fan switch the first notch sends fire to compressor the second and third notch the fan comes on but the compressor doesn't. I replaced the switch and it does the same thing. Did I get a bad switch?

 

[used red MN]

Working on the ac on my ford 7740 and when you turn on the fan switch the first notch sends fire to compressor the second and third notch the fan comes on but the compressor doesn't. I replaced the switch and it does the same thing. Did I get a bad switch?

Are you testing a known spade terminal on the switch that goes to the compressor? And when you select the 2nd and 3rd positions the power on that terminal drops off? More likely there are other control switches in the circuit going to the compressor, can you find those and see if they are by chance opening? If left alone long on 2nd speed does the compressor kick in again? If it does that might indicate low refrigerant. A wiring diagram of the system would be very helpful.

 

[NHbalerman]

Are you testing a known spade terminal on the switch that goes to the compressor? And when you select the 2nd and 3rd positions the power on that terminal drops off? More likely there are other control switches in the circuit going to the compressor, can you find those and see if they are by chance opening? If left alone long on 2nd speed does the compressor kick in again? If it does that might indicate low refrigerant. A wiring diagram of the system would be very helpful.

Ok thank you

 

[da.bees]

I was about to say turn that silver switch on other side of panel to the right but you should first check that stuff used red suggested.

 

[rrlund]

Do they use a relay somewhere? The switch in the car only worked on 3 a few years ago. I thought it was the switch, but when I took it to the shop to have them replace it, they just unplugged a relay from the fuse panel and pushed a new one in.

 

[Harry in Ky]

Working on the ac on my ford 7740 and when you turn on the fan switch the first notch sends fire to compressor the second and third notch the fan comes on but the compressor doesn't. I replaced the switch and it does the same thing. Did I get a bad switch?

As I see it there are five pins on the blower switch. One gets power from the key switch circuits. One sends power to the compressor clutch through the A/C thermostat switch and the low pressure switch. That pin is live in all three (switch on) positions. The other three are for the various fan speeds, each has power in one of the three (on) positions.

What you describe (provided the compressor clutch actually does come on) in only one position then off again in positions two and three indicates the wires on the switch are probably connected wrong. Do you have all three fan speeds? Which one is on when the clutch is on? Is the system cooling at all in this position? Too many unanswered questions for any other guesses.

 

[NHbalerman]

Do they use a relay somewhere? The switch in the car only worked on 3 a few years ago. I thought it was the switch, but when I took it to the shop to have them replace it, they just unplugged a relay from the fuse panel and pushed a new one in.

Thank you I don't have a wiring diagram or a book to show which relays does what but I do have one ordered

 

[NHbalerman]

As I see it there are five pins on the blower switch. One gets power from the key switch circuits. One sends power to the compressor clutch through the A/C thermostat switch and the low pressure switch. That pin is live in all three (switch on) positions. The other three are for the various fan speeds, each has power in one of the three (on) positions.

What you describe (provided the compressor clutch actually does come on) in only one position then off again in positions two and three indicates the wires on the switch are probably connected wrong. Do you have all three fan speeds? Which one is on when the clutch is on? Is the system cooling at all in this position? Too many unanswered questions for any other guesses.

Ok I can hot wire the compressor and it does work. At the fan switch it has power to it and first notch compressor will click but no fan 2 and 3 fan works but nothing to compressor. This is a new fan switch and it has the plug on it where it fits only one way

 

[Harry in Ky]

Still sounds like the switch is wired wrong (for whatever reason) or it's simply the wrong switch for the application. The next move is up to you, but I would be adding some jumper wires, testing the harness plug terminals one at a time to see what terminals do what when battery voltage is applied. One of course will be the switched power circuit so power there will do nothing. One will apply the compressor. The other three SHOULD be low, medium, and high blower speeds. Then test the switch terminals (jumper wire with power to the main terminal and a test light to check the other four) to see if they correspond to that. That should tell you something.

 

[paulsamwel]

Working on the ac on my ford 7740 and when you turn on the fan switch the first notch sends fire to compressor the second and third notch the fan comes on but the compressor doesn't. I replaced the switch and it does the same thing. Did I get a bad switch?

Some systems the blower switch when turned to any fan speed also sends power to thermostatic switch which relays that power through the high and low pressure switches then to the compressor.

 

[Harry in Ky]

Some systems the blower switch when turned to any fan speed also sends power to thermostatic switch which relays that power through the high and low pressure switches then to the compressor.

Can you name one that doesn't? Granted, Many machines less than ten years old (+ or -) often add a computer to the mix with additional sensors and complicated circuits, but the Ford forty series doesn't qualify.