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Low Voltage Wire Diagnostic &
Replacement Guide

Low voltage wire Diagnostic

The wire can become defective in the following ways (read repair description for a guide to explain to the client):

  1. The wire is “open” and can no longer transmit voltage or enough voltage through the wire. Simply put, there is a break in the wire.

  2. The wire is “shorted”. This means that one conductor (wire) is in contact with another conductor and the voltage is trying to transmit through one or more wires at the same time. This usually causes a fuse to blow or a part to be damaged. This can also cause components to operate improperly because they do not have enough voltage to meet what is required.

 

Whenever you find a damaged or defective thermostat wire, a replacement option must be given to the client. Even if you find a “work around” you must provide a written estimate to replace the thermostat wire. If it is not possible or plausible to replace the wire then you are to provide a written estimate to replace the needed components for the system to function, with wireless devices/controls.

 

Troubleshooting or diagnosing a defective thermostat wire.

Many times you will encounter issues with a system that lead you to believe the thermostat wire is defective (shorted or open).

Following these simple steps will provide a clear diagnosis that you can present to the client and can be achieved in a matter of minutes.

 

TAKE A PICTURE OF ALL WIRE CONNECTIONS BEFORE TAKING APART OR PERFORMING TESTS. UPLOAD THE PICTURES TO THE CLIENT RECORD.

 

You will perform two simple tests.

YOU MUST perform a visible inspection of the wires in ALL areas that are accessible (the attic, crawlspace, closets, lineset covers, etc). You have to make sure there are no splices in the wires. If there are splices, all the connections must be taken apart, inspected and reconnected.

If you identify an area where the splices need to be repaired you are to provide the client with a written estimate to repair the splice and a written estimate to replace the wire. There is no guarantee that repairing the splice will fix the problem, but you need to repair the splice to continue in the diagnostic procedure.

Perform the test on one section of thermostat wire at a time. (wire from thermostat to unit {AHU, Furnace, or Packaged Unit} wire from the indoor unit (AHU, or Furnace).

Begin by disconnecting ALL conductors in the outer jacket on both ends of the suspect section of wire.

Be sure not to cut the wire too short that it can no longer be used and “strip ALL wire ends so ½” of wire is bare on ALL wires at BOTH ends of the wire. 

Using your multimeter on the Ohms scale (see image below). 



 

 

Begin by holding one lead of the multimeter on one wire (bare copper) and then with the other lead, touch each wire (on the bare copper). Repeat the process until you have checked every wire the same way. If you get a reading of continuity (see image below), there is a “short” in the wire and it must be replaced.

 

 

The next test is similar but for this test you will “twist ALL the bare wires together on one end of the thermostat wire so that ALL the copper conductors are touching and cannot come apart.

Now using you meter at the opposite and of the wires that are all connected:

Begin by holding one lead of the multimeter on one wire (bare copper) and then with the other lead, touch each wire (on the bare copper). Repeat the process until you have checked every wire the same way. If you DO NOT get a reading of continuity, there is an “open/break” in the wire and it must be replaced.

 

Repeat the tests on ALL sections of wire, even if you find a defective section. Perform the test on one section of thermostat wire at a time. (wire from thermostat to unit {AHU, Furnace, or Packaged Unit} wire from the indoor unit (AHU, or Furnace).

 

THIS TEST SHOULD TAKE NO LONGER THAN 30 MINUTES TO COMPLETE FOR AN ENTIRE SYSTEM.

Stay focused on the task and do not get distracted, once you start do not stop until you have completed the test in its entirety as written.

 

AS ALWAYS:

Use your Guide to prepare written estimates for all recommended repairs

 

Remember to reconnect everything you took apart and restore the equipment to the condition it was when you arrive (or better)

Summary

 

Low Voltage

Low voltage components and wiring are an integral part of your home’s comfort system. Just like your central nervous system, when it isn’t working right the whole body feels out of whack.

The integrity of the low voltage wire and connections is crucial to the performance of the system and critical to prevent damage to the expensive electronics in your equipment and appliances.Today’s 21st century products need wiring of the best integrity. Over time the low voltage wiring can become degraded and no longer perform as needed. Your old system may have been working fine with the existing wiring until now. 

Wire can become degraded in many ways but the most common is simply moisture, over time the copper wiring breaks down (like an old green penny) and can no longer do its job. Most people realize it isn’t worth the risk to continue to use the old wiring 


 

Running New Thermostat Wire – When control/thermostat wires fail to conduct a proper signal a new thermostat wire from the indoor unit to the thermostat or the outdoor unit. Running a new thermostat wire can be challenging due to variances in each home's construction. The purpose of running new thermostat wire is necessary for certain reasons such as:

  • The most obvious reason is that the new thermostat requires an additional wire and there are no other wires available in the wire bundle to use for the new thermostat. 

  • The existing wire is very old and brittle which you do not trust.

  • The existing wire was damaged.

  • The existing wire is not long enough for the new terminations. 

  • The wire is “shorted” or provides an irregular signal.

  • The wire is “open” and will not allow a signal to transmit

The technician has made every effort to provide a complete diagnosis, but will not be able to fully verify there are no other problems or secondary damage until the wire/part has been replaced.

Unfortunately by the time you noticed there was a problem with the system/component, other items may have already been damaged or will fail when subjected to the stress of the system/part operating at full capacity.

At times the technician will recommend replacing additional related parts as a precaution or as standard procedure per the mfg.

 

Google Sites Low Voltage

 

Task

 

The following outline is descriptive of a typical repair, your actual repair may vary

The technician will  determine the type of HVAC system you have and the thermostat you are installing to determine the number of wires needed for the bundle.

The technician will get the wire and all the tools needed to route/fish the wire through the wall and to either the crawl space, basement, and in some cases the attic. The key is to get the new wire from where the thermostat/equipment to the desired component/equipment for the connections to the controls. In some situations the tech can use the old thermostat wire and attach it to the conductor bundles securely and use the old thermostat wire bundles to pull the new thermostat wire however, in most situations this will not be possible because usually when someone was installing the original wire they put a couple of staples into it to hold in place most likely before the drywall or plaster was put on the walls and the wall was simply studs.

Scope

Determine the number of conductors needed before you pull the new conductor bundle in the wall/house. 

Be sure to keep wire from running parallel to any line voltage wires, as this can cause problems with electronic devices and signal clarity.

 

Secure wire wires exposed with staples or ties, being sure not to crush wires

Where possible and practical follow standard color codes. 

Red - R

Blue - C

Green - G

Yellow - Y

Orange - O

White - W (W1)

Black - E (Aux/W2)

Brown - Alternate Staging

The integrity of all wire connections will be confirmed and repairs to connections made as needed, up to and including new connectors on wires. Once the new wire has been installed an operational test will be completed. If further diagnostic is needed, the diagnostic will be done as part of the original diagnostic. Any additional repairs will be approved before completing.

With advancements in electronics, some functions may vary or no longer function.

Cycle System through all modes of operation and demonstrate to the client.

Other considerations with this type of repair

Electrical Service Upgrade

Wire size upgrade

Fuse replacement

Breaker replacement

Installation of Micro Breaker   

System monitoring

Electrical component Ohm’s testing

Surge protection (Unit or Whole house)

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