Testing the Charge

• Level the cooling unit. Place the level on

the freezer bars. If the unit has no freezer bars, place the level on top of the flu. Check the level side to side and front to back.

• Reinstall the heating element and check the wattage using Ohms Law.
• Reinstall the entire boiler pack wrap.
• Using an adapter, plug the heat element into 110 AC voltage.

The last article addressed preparing the cooling unit for reconditioning. We now turn our attention to charging the cooling unit, specifically to creating the correct formula.
        Before starting, it should be noted that the following procedure requires the use of a gas and a liquid.   Safety glasses should be worn at all times and eye wash should be kept nearby. Now, we're ready to proceed.

• The unit should be completely free of charge (liquid and pressure).
• Ensure all valves on charging board are closed.
• Attach the charging wrench to the service valve. The wrench must be attached properly: straight and tight. Open the service valve by turning the handle on wrench counter­ clockwise (approximately one-quarter turn).
• There are three things you must know in order to determine the correct formula to use. They are the make and model number of the refrigerator and the size of the absorber coils.
• Determine the diameter of absorber coils (3/4 inch or 1/2 inch). Absorber coils with a diameter of 3/4 inch require a formula that fills the sight glass to 3/4 total capacity. Absorber coils with a diameter of 1/2 inch require a formula that fills the sight glass to 1/2 total capacity.
• Refer to the formula chart for correct percentages and pressures (part of the Customized Tool Kit).
• Create the formula required for that cooling unit.
• Once the formula has been perfected, discharge formula to the cooling unit.
• Pressurize the cooling unit using hydrogen.

Tapping the Cooling Unit

Of note, there are two ways to tap a unit. The method employed depends upon the type of cooling unit being serviced. A cooling unit with a service valve requires "tapping to the hiss." A cooling unit that required welding on a service valve should be "hose tapped."

Warning: The following procedure could be hazardous to your eyes. Safety glasses shall be worn at all times. Have eyewash nearby.

• Record the time 110 volts is applied to the heat element. (This will be helpful in knowing when it is time to tap the unit if tapping is necessary.)
• Allow the unit to run for approximately one hour.
• After one hour, check the steam line where it enters the condenser. The line should be hot to the touch.
• Check the absorber coils. The coil should be warmest at the bottom.
• Some cooling should now be noticeable in the freezer evaporator coil.
• If these temperatures are not present, the cooling unit requires tapping.

Tapping to the Hiss

This method is used for Dometic models and other units with a factory service valve. Proceed as follows:

• Install the charging wrench on the service valve. Do not open the service valve yet.
• The vent on the charging board should be open.
• Open the discharge valve on the charging board.
• Be in a position to view the sight glass while also controlling the charging wrench. Of note, be prepared to close the charging wrench quickly when hiss is noted.
• Open the service valve approximately one-quarter turn. Liquid from the cooling unit will be forced into the charging board. When the liquid in the absorber vessel reaches the opening in the service valve, the liquid will be replaced by vapor. Vapor escaping from the service valve will cause a hiss.
• When hiss is heard, quickly close the service valve.

 

46 RV PRO OCTOBER 2007

• Close the discharge valve. Allow the vent to remain open.
• Remove the charging wrench from the service valve.
• The freezer bar coils should begin to cool within 60 seconds. The charge is complete.

Phase Four: Leak Check

Next, spray the repaired area(s) with the W.A.P. formula. If no red appears, the cooling unit is leak-free. If a red
coloration appears, go back to Phase One:

Leak Checking. If the unit is leak-free, you are ready to paint. Of note, use industrial rust-prevention paint. Proceed accordingly:

• Paint the entire cooling unit.

Allow it to dry. Repeat.

Editor's note: This guest column is the third in a three-part series that looks at reconditioning RV refrigeration systems from a technical perspective. This article addresses charging the cooling unit.

Roger and Onna Lee Ford are the owners of Ford RV Refrigeration, a Benton, Ky., business that specializes in the field of RV refrigerator reconditioning.
The business sells a step-by-step instructional manual and customized tools needed to reconditioning RV refrigerator cooling units, offers certified technician training, and issues membership for the RV Refrigeration Network (RVRN), an association of businesses that provide RV refrigerator reconditioning services. For more information, visit the company website at www.rvrefrigeration.com. To contact the Fords, call 877­ 378-3744 or    e-mail them at fordrv@rvrefrigeration. com.

Once the leak or leaks in the cooling unit have been repaired and you have done a final leak check with the WAP. formula, you are ready to paint and charge the cooling unit.

Reconditioning RV Refrigeration Systems, Part 3

(EDUCATION)

Hose Tapping

This method is used for Norcold models. Proceed as follows:

• Open the vent on the charging board. All other valves on the charging board should be closed.

• Open the charging wrench on the cooling unit and fill the hose with liquid from the cooling unit.

• Close the charging wrench.
• Open the discharge valve to release the pressure in the discharge line .
• Close the discharge valve.

• Apply multiple coats to the boiler area and the evaporator area.

Once the paint is completely dry, you are ready to urethane. Urethaning is demonstrated in the training. The Ford Procedures technique is customized for each individual unit in order to create the only true perfect seal.

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Reassembly

We now move to reassembly. A word of caution: It is critical that you reinstall insulation between the flue tube and the steam line. Be sure to have adequate insulation between the cabinet and the boiler. The next step is to reinstall the heat element and boiler pack around the boiler.

We now turn our attention to the cooling unit. Proceed accordingly:

• Accurately reassemble the cooling unit, burner assembly, controls, and wires.
• When all the gas connections have been made, leak check all the connections. Operate on gas and leak check again.

Phase Three: Leak Check: (Running in the Raw)

Next, bagatize the unit and run it over­ night. The next day, the unit should have frost on the evaporator and other indications that the unit has been correctly repaired and charged.

Some may feel that our leak checking procedures are taken to the extreme. However, this is one of the reasons warranty claims are extremely rare.

Of note, if no ammonia odor or discoloration is noted, proceed to Phase Four.

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Final Test

• Bypass the controls, as shown in the August issue of RV PRO.
• Place a thermometer in the refrigerator compartment and allow it to run overnight. Check the refrigerator temperature the next day. Regard­ less of ambient temperature, the thermometer in refrigerator should read below 32 degree Fahrenheit.
• If the temperature is satisfactory, reconnect the controls.
• Allow the refrigerator to run 24 hours on electric and 24 hours on gas to ensure that all operating systems are 100 percent.

The average hands-on work-time on the cooling unit is six hours. The average cost for materials to recondition a cooling unit is profitable.

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