Can You Fix A Pto Clutch No Resistance

By Richard Hawkins, MACS contributor

Checking the clutch air gap before installing a compressor is an important step in compressor installation. This is because of the possibility of a clutch air gap getting knocked out of adjustment due to crude handling or it being gapped incorrectly at the manufacturing plant.  These issues of course can cause bug with clutch operation.  If detected and corrected earlier compressor installation, a lot of time can exist saved.

There are two other "correct out of the box" clutch problems that are encountered with some regularity on tech line calls.  These are:

1.  No clutch function at all. (Usually due to an "open up" clutch coil.)

2.  The A/C compressor clutch circuit bravado fuses.  (Normally due to clutch coil resistance beingness too low.)

Equally a result, it is appropriate to do some other tests while you accept the compressor on the bench checking the clutch air gap.

These tests are:

• Bench testing the clutch to make sure it will function.
• Then checking the resistance of the clutch curl.

Bench testing the clutch for function is easily accomplished. This can exist done by just putting power and ground directly to the clutch coil.  This can exist done utilizing a battery and test wires or a power probe.  If using test wires, an in-line fuse holder with a 10-amp fuse should be utilized for protection and the test wires should be 16 judge or larger.  Equally before long equally power is applied, the clutch should engage. When power is removed, it should immediately undo. CAUTION: Polarity must be observed when doing this examination.  If the wires are connected wrong and the clutch coil uses a diode, diode impairment will result.

The nigh common cause of compressor clutch circuit fuses blowing is a compressor clutch coil having a resistance value which is too low.  Taking an ohmmeter and checking the clutch coil resistance will apace tell you lot the resistance.  If your information system provides the resistance value for the specific vehicle you are working on, it is best to use that.   However, it does non seem to be readily available for very many vehicles.

Fortunately, the mobile A/C industry provides some guidelines on this.  If you search Google for "A/C compressor clutch resistance" at that place are several articles that come up with clutch coil resistance data.  Unfortunately, at that place isn't universal agreement on the specifications.  Some of the ranges that will be seen are:  "ii.0 to under 4.five ohms", "two.viii to iv.4 ohms", "around 3.0 to 4.0 ohms", three.0 to 5.0 ohms" then the widest range which is "two.0 to 5.0 ohms".  A short discussion with someone working on a tech line too yielded the answer: "iv ohms plus or minus ane ohm" (which of grade is the range of three.0 to 5.0 ohms.)  (These values are for 12-volt clutches only.)

Utilizing all that information, the lowest adequate resistance value would exist ii.0 ohms and the highest acceptable resistance value would be v.0 ohms.  And so, two lines could be drawn in the sand there with anything that checked below 2.0 ohms or above 5.0 ohms being disqualified.   (Go on in mind that these resistance values are at room temperature. Resistance readings taken at extreme temperatures can be afflicted. Lower temperatures crusade resistance to get down.  Higher temperatures cause resistance to go upwards.)  Encounter picture #1.

Pic #1: An ohmmeter test of the clutch curlicue tin can tell yous if resistance is inside an acceptable range.  Nevertheless, exist sure y'all have good connections or the readings on the meter may be misleading. Many clutches take 2 wires running to them.  The one in this motion-picture show has 1 wire and is grounded through the compressor instance.

But you might say: That leaves a lot of grey area with all the other ranges that fall within the ii.0 to 5.0 range.  How do we accost that?  Taking all of that into consideration, the "sweet spot" seems to be from about iii.5 to 4.0 ohms, then it becomes something of a judgment call.   If you check the clutch coil resistance and it is outside of iii.5 to iv.0 ohms, it would be a good idea to contact the compressor supplier and come across what they say.

Some technicians like to get a step further and check the amperage with an in-line amp meter.  To make up one's mind what the amperage should be, we would use Ohms Law:  Amperage = Voltage divided by Ohms.  Here is an instance using a fully charged battery with 12.65 volts every bit a power source and a clutch coil with 4.0 ohms of resistance.

12.65 ÷ four.0 = 3.1625 (And then the amperage would exist just over 3 amps.)

As was the case with the air gap issues, clutch roll resistance issues and non-operation clutches are not an everyday matter. However, if you do enough A/C piece of work, it is highly probable you will run into a non-functioning clutch or clutch coil resistance result somewhere along the line. Equally fate might have it, it will probably exist on a vehicle where the compressor is buried and removing and re-installing another compressor might accept hours. You'll find taking a few minutes to check clutch function and the clutch gyre resistance can prevent this from occurring.

An excellent article on clutch function tin can be found at the following link: https://www.macsw.org/WEB/images/Macs_Docs/2019TETS/TCCI.PDF

Available in archives to MACS members but. Bring together MACS as a member to use the members only archives and technical resources. One of the many benefits of MACS membership.

Can You Fix A Pto Clutch No Resistance,

Source: https://macsmobileairclimate.org/2021/09/07/facts-to-know-about-the-compressor-clutch-coil/

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