Service Hotline: 08/05/2002
By Scott Ehaney
I have a question concerning the proper evacuation of a refrigeration system before charging. We are an OEM of commercial bar equipment using R-134a compressors ranging from 1/4 to 1 horsepower.
We are trying to define our refrigeration process. Currently we pre-evacuate for 15 minutes to about 500 microns. Then each system is hooked up to a Galileo charge board until it is pulled to 30 microns before charging.
I know some manufacturers only pull the system down to 200 microns before charging.
From Dan Kramer
Patent Attorney and Specialist Grade Member of RSES
Evacuation has a two-fold purpose. The first is to remove any residual moisture. The second is to remove air and other non-condensibles.
Liquid water at 32 degrees F exerts a vapor pressure of about 4,600 microns (0.089 PSIA). Therefore, so long as your system is at room temperature and it can maintain a pressure of less than about 1,000 microns with the pump off, you can be quite sure there is no liquid water present.
While it is true that water can be frozen simply by reducing the pressure over it, so long as the system is kept warm during evacuation, such freezing is unlikely. Maintaining a warm system at a very low pressure for a reasonable time period, such as 15 minutes, helps the water and air dissolved in the oil and adsorbed in the drier and on the interior metal surfaces to be desorbed and removed.
The mass of air and remaining water vapor will be directly proportional to the pressure in the system before charging. With the system pressure at 1,000 microns at charging, the mass of remaining gases will be 1/760 of the original mass of gases residing within the system. Naturally, the lower the ultimate pressure before charging, the less will be the mass of gases remaining.
With the old refrigerants and mineral oil, I would have said about 400 or 500 microns would have been satisfactory. However, because of the greater apparent reactivity of the new lubricants, I would say the lower the final pressure, the better.
By Charles Lewis
Glen Head, NY
I need help on a GE refrigerator, Model TBX21MAXERAA. I found the refrigerator iced up. I defrosted it, cleaned it, and changed the defrost timer and mullion heater.
A short time later I got a call about the same problem. I discovered an iced-up evaporator. The door seals were okay.
I installed a six-hour defrost timer (WR9X480) with the heater (WR51X356). But I feel I did not solve the problem.
Do you have any advice?
From John ‘Jack’ Healy
Former RSES International President
Colorado Springs, CO
There are three components that make up the defrost system in your GE refrigerator. Any one or all three could become defective.
From your question, I find that you have replaced two of the components. If they were correct for the model, the system should defrost automatically. The correct parts numbers are WR51X0356 for the mullion heater and WR9X520 for the defrost timer. The timer is very important as it controls the length of time between defrost cycles and the length of time of each cycle.
The third part is a 160 degree defrost terminating thermostat, which controls the temperature of the defrost cycle.
Since both the defrost mullion heater and defrost timer have been replaced, I would now replace the defrost terminating thermostat. It is mounted on the incoming frost tube and controls the temperature during the defrost cycle to ensure the temperature during the defrost cycle does not damage any of the material around the cycle and defrost heater assembly.
The surest way to check this thermostat is to wire around the thermostat and turn the defrost timer by hand into a defrost cycle. If the mullion heater does not heat by hand, then replace the terminating defrost heater. Once again, double-check your part numbers of the defrost timer as this is very important to the defrosting system.
Name Withheld By Request
I have my Universal Certification for refrigerants. After reading the regulations about purchasing refrigerants, I have a concern.
The company I work for buys the refrigerant we use through our purchasing agent and uses one of the technicians’ certification numbers.
When that refrigerant is received by the agent, whose responsibility is it: the purchasing agent or the technician whose certification number was used?
I’m a little confused over this area and with my number to be used for purchasing, I’d like to know if I’m responsible for all the refrigerant that comes in, or just what I charge out of the stockroom.
From Julius Banks
Stratospheric Protection Division
United States Environmental Protection Agency
The sales restriction on CFC and HCFC refrigerants went into effect on Nov. 14, 1994. Under the sales restriction, the following persons can purchase refrigerants:
Wholesalers are legally responsible for ensuring that people who purchase refrigerant from them fit into one of those categories of people who can purchase refrigerant under the sales restriction.
Wholesalers may sell refrigerant to an authorized representative as long as the purchaser provides evidence that he employs at least one certified technician. It is the wholesaler’s responsibility to determine whether persons are indeed authorized representatives.
When an employer uses a technician’s card to purchase refrigerant, the individual technician is not responsible for refrigerant that he/she is not using. However, the venting prohibition and the associated required practices are requirements that persons opening an appliance must follow, regardless of who purchased the refrigerant.
For assistance with questions related to stratospheric ozone protection and the EPA regulations, I suggest that readers call the Ozone Hotline (800-296-1996). The Ozone Hotline is open between 10 a.m. and 4 p.m. Eastern Time, and can provide immediate answers to questions or connects callers with appropriate EPA personnel.
In addition, our website (www.epa.gov/ozone/title6/608/608fact.html) addresses the most common questions concerning Section 608 regulations.
Sidebar: Contacting The Service HotlineDo you have a technical question for the pros? Submit your Service Hotline questions directly at The News home page. You may also contact refrigeration editor Peter Powell at 847-622-7260; 847-622-7266 (fax); or firstname.lastname@example.org (e-mail).
Publication date: 08/05/2002