“When the engine is started, a 'wake-up/turn-on' signal is sent to the regulator. Traditionally, this circuit is the ground side of the charging system bulb in the instrument cluster. When the regulator recognizes this voltage, it powers up the field and the charging process begins as the alternator rotates. The regulator then uses this same circuit to ground if it determines the system is not working correctly.”

Most technicians consider a charging system failure one of the easier problems to diagnose. Drive the vehicle in, check alternator output, verify the circuits and wiring are OK, and in most cases, replace a defective alternator. What could be simpler than that? After all, some systems only have two wires: one to B+, the other to the charging light circuit in the dash. So, if it's this simple, how can an alternator work fine on a test bench and be totally dead on the vehicle?

Alternators produce current by rotating a magnetic field across several windings, which produces an AC current. This current is directed though a series of diodes, which change it into DC current. The regulator controls output based on the electrical demand of the vehicle and battery. No rocket science here.

The regulator has another job and that's where the problem often occurs. When the engine is started, a "wake-up/turn-on" signal is sent to the regulator. Traditionally, this circuit is the ground side of the charging system bulb in the instrument cluster. When the regulator recognizes this voltage, it powers up the field and the charging process begins as the alternator rotates. The regulator then uses this same circuit to ground if it determines the system is not working correctly. Changes in how this "turn-on" circuit is controlled causes problems for many vehicles. Instead of ordinary bulbs, many instrument clusters now use a low current LED. Other clusters are now controlled by the electronic control module (ECM), which sends the "wake-up" signal to the alternator. The function of the circuit is the same, but the newer designs use a very low amperage flow, and in many cases, reduced voltage, as low as 5 volts. Neither of these signals will illuminate a conventional test light and must be checked with a digital volt/ohm meter (DVOM). A few systems will not send out the "wake-up" signal until the engine is running!

This brings us back to the original problem. Some voltage regulators are not sensitive enough to recognize the low amperage, low voltage signal sent to them. This is why they never "wake up" the alternator on the vehicle, but when energized by a 12-volt source on a test bench, they work perfectly. The solution is to use an alternator with the correct regulator for the application. Charging systems are still simple to diagnose; just watch out for a few twists in the road!

Dave Martin is an Identifix GM specialist. To pay his way through college, Martin started a business he named Auto Repair at Your Home. It was so successful he ran his own shop for 10 years. He is ASE master and L1 certified. Martin helped rewrite the L1 test.

My AC Works Backward!

“For many years, Ford was very consistent in the way it controlled the wide open throttle (WOT) AC relay inside that box. Traditionally, the WOT AC relay was a normally closed relay.”

Back in 1986, with the introduction of the Ford Taurus and Mercury Sable, Ford Motor Co. started using a little black box to control numerous functions including air conditioning, cooling fans, fuel pump operation and powering up the powertrain control module (PCM).

This black box has had numerous names over the years including integrated relay control module (IRCM), constant control relay module (CCRM) and variable relay control module (VRCM). It has also found its way into numerous other models including the Thunderbird/Cougar, Mustang, Windstar, Mark VIII and the Escort/Tracer.

For many years, Ford was very consistent in the way it controlled the wide open throttle (WOT) AC relay inside that box. Traditionally, the WOT AC relay was a normally closed relay. If the PCM detected a condition that required turning the AC compressor off (wide open throttle, excessive engine temperature, or no AC 'on' input to the PCM), it would ground pin 22 of the module. This would open the contacts of the relay, causing the AC compressor to lose power and turn off.

Around 1997, Ford changed the system operation so that on some models, the PCM actually grounds pin 22 of the module to turn the AC compressor ON. This would not be such a big deal except that Ford started selling the wrong parts to customers and they don't work right!

The particular vehicle I am referring to is 1998-1999.5 model year Escort ZX2s. The ZX2s that were built until Feb. 14, 1999 used a CCRM that needs to have the AC relay grounded to turn the AC on.

The problem is that Ford started selling CCRMs that were wired like the other models where the PCM grounds pin 22 to turn the AC OFF. So when the PCM grounds the circuit to turn on the AC compressor, it actually turns it off. And just the opposite happens when you turn the AC off from the control switch - the AC compressor actually comes on!

The easiest way to determine which system you have is to look at the high-pressure switch for the AC system. If it is a three-wire connector, it is actually a sensor, and requires the early CCRM. If it is a four-wire connector, it is a switch and it requires the late CCRM. Now you'll know why that new CCRM seems to make the AC work backward!

FORD Part Numbers:
1998-1999.5 with a sensor F8CZ-12B577-AC
Newer models with a switch F8CZ-12B577-BC

Bob Mordorski is an IDENTIFIX Ford specialist. He is ASE master and L1 certified with nine years of diagnostic and repair experience.

This information is provided by IDENTIFIX®. IDENTIFIX® resources cut diagnostic time and provide repair solutions that increase the shop's bottom line. From Repair-Trac pattern failure quick fixes, to Diagram-Online wiring diagrams by fax, to the Repair Hotline staffed by 32 master techs who specialize in diagnosing complex problems by phone or fax, IDENTIFIX® helps techicians fix more cars in less time. For more information on IDENTIFIX, call (800) 288-6210, 8 a.m. - 6 p.m. Central Time. www.identifix.com. © 2011 IDENTIFIX. All Rights Reserved. © 2006 IDENTIFIX. All Rights Reserved.

RATE THIS ARTICLE What do you think of this article? Your input will help AutoInc. develop additional articles on this subject. Share your thoughts! Your name Your e-mail address

MOST ACCESSED ARTICLES Fuel Injection Service, Not Just Cleaning The Art of Extraction EGR Systems: Operation and Diagnosis Proactive Target Marketing:_Rethinking Your Business Strategy Engine Performance: HO2S Diagnostics MOST E-MAILED ARTICLES Developing Employee Potential How Critical Thinking Can Help Your Business How to Diagnose the Ford Glow Plug What to Look for When Shopping for the Right Shop Management Software Putting a Price Tag on Complaints

AutoInc. Web Site | ASA Web Site | EPA Finalizes Service Information Regulation | AutoInc.'s 13th Annual Shop Management Software Guide | The Next Consolidation | New Tax Bill Scorecard | Guest Editorial | Tech to Tech | Tech Tips | Shop Profile | Net Worth | Stat Corner | Chairman's Message