LT 1 air conditioning compressor wiring

WZ JUNK · June 04, 2005, 07:05:00 AM

I am wiring the air conditioning compressor on a 1996 LT 1 Chevrolet engine. The compressor has two wires to the clutch. One of these appears to have a diode. What gives with the extra wire and the diode and how do you wire this compressor?

PeterR · June 04, 2005, 08:48:20 AM

Quote from: "WZ JUNK"I am wiring the air conditioning compressor on a 1996 LT 1 Chevrolet engine. The compressor has two wires to the clutch. One of these appears to have a diode. What gives with the extra wire and the diode and how do you wire this compressor?

The wire with the diode most likely went to an auxiliary electric fan. The diode allows the fan to always operate when the aircon is on, and also to be operated from another circuit (for example a temp switch) without sending power back up the wire to the clutch.

WZ JUNK · June 04, 2005, 08:59:48 AM

Quote from: "PeterR"
Quote from: "WZ JUNK"I am wiring the air conditioning compressor on a 1996 LT 1 Chevrolet engine. The compressor has two wires to the clutch. One of these appears to have a diode. What gives with the extra wire and the diode and how do you wire this compressor?

The wire with the diode most likely went to an auxiliary electric fan. The diode allows the fan to always operate when the air conditioning is on, and also to be operated from another circuit (for example a temp switch) without sending power back up the wire to the clutch.

So, I plan to use a relay in this circuit and use the air compressor clutch wire to trigger the fan relay. This way anytime the air compressor is on the electric fan is on. If I do it this way, I will not need to worry with the diode as the relay will isolate the fan. Tell me if I am wrong.

PeterR · June 04, 2005, 11:49:12 PM

Quote from: "WZ JUNK"

So, I plan to use a relay in this circuit and use the air compressor clutch wire to trigger the fan relay. This way anytime the air compressor is on the electric fan is on. If I do it this way, I will not need to worry with the diode as the relay will isolate the fan. Tell me if I am wrong.

You are correct if the fan is only activated by the clutch. However is it common to have aux fans wired so they come on whenever the clutch is energised, and also if the water temp creeps up even when the aircon is off. This requires isolation of the two circuits or power can back-feed to the clutch when the radiator switch closes.

The radiator switch can be wired in two ways.

As a "power switch"
A power feed from the ign runs to one terminal on the switch, then from the other switch terminal to a coil terminal on the relay. The other coil terminal is permanently grounded. When the radiator switch closes, power is applied to the relay coil and the relay closes kicking in the fan.

As a "grounding switch"
A power feed from the ign runs to a coil terminal on the relay, the other coil terminal runs to the radiator switch which grounds it when closed.

If you have a power switch, then you can use the parts already fitted. Just run a lead from the diode and splice it into the wire that runs from the radiator switch to the relay coil. This means power from the switch or from the clutch will close the relay. If the aircon is off, but the water is hot enough to close the radiator switch, then power will be fed to the relay coil but the diode blocks power running back to the clutch.

Or you can fit another relay in parallel with the rad switch relay. The rad switch relay wiring is not touched, and the second relay has one coil terminal permanently to ground, and the other fed from the clutch wire.

If you have a grounding radiator switch, then the simplest method is definitely to run a second fan relay in parallel. The rad switch relay wiring is not touched, and the second relay has one coil terminal permanently to ground, and the other fed from the clutch wire.

WZ JUNK · June 05, 2005, 10:09:45 AM

Quote from: "PeterR"
Quote from: "WZ JUNK"

So, I plan to use a relay in this circuit and use the air compressor clutch wire to trigger the fan relay. This way anytime the air compressor is on the electric fan is on. If I do it this way, I will not need to worry with the diode as the relay will isolate the fan. Tell me if I am wrong.

You are correct if the fan is only activated by the clutch. However is it common to have aux fans wired so they come on whenever the clutch is energised, and also if the water temp creeps up even when the aircon is off. This requires isolation of the two circuits or power can back-feed to the clutch when the radiator switch closes.

The radiator switch can be wired in two ways.

As a "power switch"
A power feed from the ign runs to one terminal on the switch, then from the other switch terminal to a coil terminal on the relay. The other coil terminal is permanently grounded. When the radiator switch closes, power is applied to the relay coil and the relay closes kicking in the fan.

As a "grounding switch"
A power feed from the ign runs to a coil terminal on the relay, the other coil terminal runs to the radiator switch which grounds it when closed.

If you have a power switch, then you can use the parts already fitted. Just run a lead from the diode and splice it into the wire that runs from the radiator switch to the relay coil. This means power from the switch or from the clutch will close the relay. If the aircon is off, but the water is hot enough to close the radiator switch, then power will be fed to the relay coil but the diode blocks power running back to the clutch.

Or you can fit another relay in parallel with the rad switch relay. The rad switch relay wiring is not touched, and the second relay has one coil terminal permanently to ground, and the other fed from the clutch wire.

If you have a grounding radiator switch, then the simplest method is definitely to run a second fan relay in parallel. The rad switch relay wiring is not touched, and the second relay has one coil terminal permanently to ground, and the other fed from the clutch wire.

Thanks Peter, I am going with the two relay approach as the fan sensor switch is the grounded type. I have two wires on the compressor, one is the green one with the diode and the other is black. I am thinking the black one is a ground. I will check it with my ohm meter but it is hard to see much on this application as the compressor is underneath the alternator on the bottom right side of the engine. It would be a lot easier if I knew for sure the black wire was a ground.

PeterR · June 05, 2005, 11:08:44 AM

QuoteI have two wires on the compressor, one is the green one with the diode and the other is black. I am thinking the black one is a ground. I will check it with my ohm meter but it is hard to see much on this application as the compressor is underneath the alternator on the bottom right side of the engine. It would be a lot easier if I knew for sure the black wire was a ground.

This throws new light on the subject. I had interpreted your first post as indicating the lead with the diode was spliced into the main feed wire.

Most automotive aircon clutches have one feed wire and the other end of the coil is grounded by a rivet on the mount plate behind the pulley. A clutch which looks identical except that they have a black earth lead and green power lead is used in marine applications for winches and auxiliary drives. (The reason for bringing out the earth lead is to provide a reliable ground rather than a rivet which corrodes easily and can not be checked after assembly.)

This style might also be used in some auto applications, or perhaps the original one-wire type has been replaced at some time.

To make testing easier I suggest you push a sewing needle through the insulation of the green wire on the coil side of the diode then use the ohm meter to measure the resistance between the needle and the black lead, and also between the needle and the end of the green lead. In both cases measure then swap the pos and neg meter leads and measure again. The coil will have about 4ohms in both directions; the diode will be open in one direction and low reading in the other.

WZ JUNK · June 05, 2005, 11:22:15 AM

Quote from: "PeterR"
QuoteI have two wires on the compressor, one is the green one with the diode and the other is black. I am thinking the black one is a ground. I will check it with my ohm meter but it is hard to see much on this application as the compressor is underneath the alternator on the bottom right side of the engine. It would be a lot easier if I knew for sure the black wire was a ground.

This throws new light on the subject. I had interpreted your first post as indicating the lead with the diode was spliced into the main feed wire.

Most automotive aircon clutches have one feed wire and the other end of the coil is grounded by a rivet on the mount plate behind the pulley. A clutch which looks identical except that they have a black earth lead and green power lead is used in marine applications for winches and auxiliary drives. (The reason for bringing out the earth lead is to provide a reliable ground rather than a rivet which corrodes easily and can not be checked after assembly.)

This style might also be used in some auto applications, or perhaps the original one-wire type has been replaced at some time.

To make testing easier I suggest you push a sewing needle through the insulation of the green wire on the coil side of the diode then use the ohm meter to measure the resistance between the needle and the black lead, and also between the needle and the end of the green lead. In both cases measure then swap the pos and neg meter leads and measure again. The coil will have about 4ohms in both directions; the diode will be open in one direction and low reading in the other.

I will go back to the shop in a moment and try to do what you just mentioned. I did check to see if the black wire was a ground and it does not appear to be as I did not get continuity between it and the compressor housing. I did get continuity between the green wire with white stripe that has the diode and the and the black wire. However, yesterday I tried positive voltage to both of these leads and I could not hear the clutch engage.

PeterR · June 06, 2005, 04:42:10 AM

QuoteI did check to see if the black wire was a ground and it does not appear to be as I did not get continuity between it and the compressor housing. I did get continuity between the green wire with white stripe that has the diode and the and the black wire. However, yesterday I tried positive voltage to both of these leads and I could not hear the clutch engage.

The coil is fully insulated from the body. One end of the coil winding wire comes out as a supply lead –usually green.

either
The other end of the coil winding wire has a short lead exiting from the coil and terminated under a rivet on the square mounting plate. This is behind the pulley and can not be seen when the unit is assembled. Power is applied to the green lead and the compressor body provides the ground.

or
The other end of the coil winding wire comes out beside the power lead and has to be grounded on the compressor or engine block. If this type, there will be no internal connection between either lead and the compressor body. The clutch will only engage if the black is grounded externally and the green has power.

From your description it would seem you have the second type and this would be confirmed by the meter showing about 4ohms between the leads, and neither connected to the compressor body.