Chromeshadow

Only a micro-ohmmeter can constantly measure low resistant circuits-a standard meter cannot. They use 10A or 100A as their current source and 4 wire "Kelvin" measurements. The resistance in a standard meter test leads is higher than the resistance in your battery cables. The specs on a Fluke 77 on the lowest range are 320.0 Ohm +-(.05%+3). this means if you are measuring 1 Ohm resistance your meter may be reading 1 ohms, plus (.05% of reading) 0.005 ohms, plus (three digits) .3 ohms, for a total of 1.305 ohms, or you could be trying to measure .3 ohms and the meter may read zero. If you have a .3 ohm battery cable-the max current you'll be able to get to your starter is 40A, way short of the 300A you need.
The AC clutch is a similar circuit,I like to use the voltage drop test for this, but this circuit is much harder! The AC Clutch has a couple of connections and switches that can switch voltage but can have high enough internal resistance (bad switch) that they can fool a meter into thinking the circuit is OK but when the clutch tries to kick in, the voltage at the clutch drops low enough that the clutch will not engage. If I was checking this every day and I had a light I trusted, I would use it. If not, I'd use and old style tail light with jumper clips to load the circuit. It never hurts to have more than one way to test an expensive part!!

You can use the voltage drop technique if you have some current flow. I have been fooled when using a meter lots of times into thinking that a circuit is OK because it had the correct voltage, (tail lights and AC clutch), but when I put the bulb back (or hooked up the clutch) it did not work. I don't like test lights, but there are times they will give you a better answer than a meter.
My Credentials? I have a degree in electronics, 9 years as a electromechanical field service engineer before I went into sales. I know how to use everything I sell, and I help write the specs and I know what they mean. Btw, I never give absolutes in testing, there is always an exception to rules, even if I don't know the reason why. Feel free to take my opinion or leave it, I just hope my comments help someone understand a little more about testing higher current circuits.

jwog666

its nice to have someone else who know something post on this thread

jwog666

you are the least knowledgeable person on electrical systems that claims to be an expert i have ever run across. claiming that u are ASE certified in electrical means that you took a test that any high school student could pass, and also is so general that it doesnt relate to 99% of what people will encounter repairing vehicles in the real world. please do everyone a favor, and stop giving people bad advise. go troll OP instead.

oxfordgt

Well you can listen to the test light jockeys or you can listen to me and the ford shop service manual. Here is a free download http://www.mediafire.com/download/ao...ual+backup.pdf I'm done with the ignorance in this thread.

jwog666

i would listen to the people who work on CARS professionally. when i went to training with Ford to become Senior Master Certified , they said exactly what i am saying about using a test light. so i guess the people who engineer and build the cars and then train their techs to work on them are wrong? if you would like i could get a response from the FSE (field service engineer) for our region that will back me up. however since he is usually busy helping techs fix hard to diagnose issues, he may not have time to help me correct a putz on a forum.

oxfordgt

Now you wanna call names like a child? Ok ********, so he puts a test light on the connector and it doesn't light meaning it doesn't have 12v. guess what he already ****ing knows that Now he has to do the correct testing with a DMM to find the problem so he can fix it. You must work at a ford dealership because you are as stupid as every other ford tech I've met. When you design your own electrical circuits for an entire car or build, diagnose and fix $100k race cars then you talk ****. stupid mother ****er

jwog666

blah blah blah, your true intelligence is showing lmao

sweetbeats

So, jwog666 and chromeshadow, I have a Fluke 85 DMM, used it a lot...I repair/troubleshoot/upgrade pro audio equipment. So I understand the value of troubleshooting circuits under load. There's been a bit of noise on this thread. So to get back to next steps, I was going to first of all use my variable bench supply to apply 12VDC to the A/C clutch and just confirm it engages to rule that out, then start tracing back to determine where the voltage is being divided in circuit that powers the A/C clutch. Is that sound?

jwog666

absolutely, dont forget to check in the fuse box, look at the ac clutch relay and diode to see if the terminals there are corroded

jwog666

i notice in your other post your alt is most likely bad, if your system voltage is low due to a bad alternator, the 9v you are reading at the compressor might be caused by a discharged battery? i would get the alt fixed first then check the operation of the clutch