I have a voltage drop at my A/C compressor. My MM shows 10.89 volts. Not enough to start the clutch. If I jump it it kicks right in so it's not the compressor. The positive current comes from a small guage orange wire. It enters the large wire loom underneath the group of fusible links behind the battery. Based on the direction that it enters I'm assuming it is a part of the harness that travels behind the grill to the other side of the engine bay.

Anyway, does anyone know wher the wire ends up? Also can a bad ground reduce voltage? If so where is the ground wire?

 

Have you been to my website and completed Tips 1 through 5 yet?

I wouldn't waste any more time looking until those are completed.

 

I haven't completed 4 & 5 yet but I don't think they would affect the AC voltage. Would they?

 

Could be that Tip2 wasn't done well enough regarding the 4 relays and their sockets.

 

They looked good but i cleaned them again. No love.

When I jump start the compressor it remains on when the jumper is removed. That makes me think that although there's enough juice to run it there's not enough to start the clutch.

Is the relay in the picture only for the AC? I pulled the relay with the engine running and it shut everything down. Is that.to be expected?

 

87 could be different. Try this. Clean all the receptacles and move the relays down one position in the line,

 

A magnetic clutch draws the same current at any point of its engagement. It is not a motor that draws a higher amperage during initial startup. If you are experiencing a voltage drop, there are many other components you are contending with. The compressor grounds through the engine via the block ground strap. The a/c clutch relay is fed through the blower switch via the blower fuse. There is also a pressure switch in series with it, as well as a diode for the electric cooling fan and thermostatic switch on the same circuit. You also have a shunt diode at the compressor clutch itself.

 

Thanks guys. Some good things to look at. I keep my XJ at my weekend place out in the desert but I'm now home for the week. I hope to be out there Friday to carry 9n.

 

AJ, if the current needed is constant why does it continue to run after I remove the jumper wire?

 

Disconnect the wire at the compressor, and use the meter to measure the resistance back to the relay socket. If you can measure the voltage at the relay with it installed and at the fuseblock that would be informative as well. Another possibility is high resistance through a/c pressure switches.

 

I can't diagnose your particular condition through a forum. But what I do know is this. The air conditioning compressor clutch is disengaged when there is no need to compress the refrigerant gas, be it that the a/c is off or the thermostatic switch indicates the evaporator is cold enough. When the compressor has to start compressing the gas again to start the super-heat/sub-cool process, a relay closes and sends 12 volts to a magnetic coil inside the clutch assembly. The force created by the electromagnet pulls the clutch inward towards the compressor... a spinning clutch engages and is held against a stationary plate, just like a manual transmission clutch engaging a flywheel. As long as power is applied to the electromagnet, the clutch remains pulled into the compressor plate. Once the relay opens, and power is disconnected from the coil, the plates should separate and the compressor stops compressing gas. The purpose of the clamping diode at the compressor is to shunt current spikes as a result of the magnetic field collapsing when voltage is removed from the coil. Is your clutch sticking or lagging when disengaging?

There are other paths for voltage to go to, or come from if other components fail, that can affect the voltage at the compressor coil. Partial voltage at the coil could be the result of the engine fan diode failing and voltage making its way to the coil when the engine fan is engaged for high engine temperatures, for example. Perhaps you might list in some sort of order what you tried, what you found, and the outcome of whatever you did. This would help us further help you. For instance, you mentioned you "jumped" the a/c relay if I recall one of your posts correctly? I presume you mean you removed the a/c clutch relay and installed a wire between the normally open contacts to mimic the relay being energized? What was the voltage at the coil after doing this? What is/was the voltage at the coil with the coil disconnected? Does the relay's internal contacts have too high of a resistance indicating a failed relay? Have you measured the resistance between the compressor and the negative battery post or the body? Or, have you checked compressor coil voltage against the engine bracket AND the negative post to compare? ...etc.

 

That's not true. A solenoid has an inrush current and higher current draw until it reaches the end of it's stroke. Also, if the voltage is too low and there is friction then it may not initially move but will have enough power to hold.

 

The a/c coil producing a magnetic field of this size will not have an inrush current that he can measure with common shop-grade equipment, and the fraction of time it would last by moving its short distance to spin the compressor will be negligible to a standard automotive fuse. It's not moving but a fraction of an inch, and for a period of time that would need an oscilloscope or a recording meter to measure.

And, if a clutch is going to stick while being energized, it will have the same frictional coefficient moving the opposite direction. Even if that came into play, he still would need to find the source of the lower voltage being present and repair that.

I am not going to start a qualifications rebuttal here. Agree with me or not, it makes no difference to me.

 

Regardless of why it might not engage but can hold with the lower voltage, the root problem is still the lower voltage. He needs to resolve that regardless.