Pumpdown Systems

From Eric Hersbrook

Eastpointe, MI

Answer:

By Daniel Kramer, P.E.

Patent attorney and former

chief engineer, Kramer-Trenton.

Referring to 40CFR82.156, which is in the Code of Federal Regulations: Title 40 — Protection of Environment Subpart F — Recycling and Emissions Reduction, we find Section 82.156, Required Practices:

“(a) Effective July 13, 1993, all persons disposing of appliances, except for small appliances, MVACs, and MVAC-like appliances, must evacuate the refrigerant in the entire unit to a recovery or recycling machine certified pursuant to Sec. 82.158. All persons opening appliances except for MVACs for maintenance, service, or repair must evacuate the refrigerant in either the entire unit or the part to be serviced (if the latter can be isolated) to a system receiver or a recovery or recycling machine certified pursuant to Sec. 82.158. Effective January 9, 1995, certified technicians must verify that the appliance level of evacuation has been reached in the appliance or the part before it is opened.”

This says that you may employ the system compressor to pump the low side down into a system receiver to service the thermal expansion valve. Note, however, that if the system does not have a system receiver, you must employ a certified recovery or recycling machine to remove the system charge before performing the repair.

In either case, if you are a certified technician, you must verify that the required pressure has been reached before the system is opened. While “verify” probably only means that you have looked at your gauge, I would keep a record on your invoice of the pressure reached before the system is opened.

Brazing Troubles

From Larry Ball

Las Vegas, NV

I have a problem brazing copper to aluminum. There are a lot of air conditioning systems in the field that have copper-to-aluminum connections.

I can braze clean aluminum to aluminum using Harris Al-Braze 1070 and an Engelhard aluminum soldering kit. I can even braze aluminum to copper with Al-Braze 1700, even though it is not recommended.

The problem is brazing copper and aluminum with oil in the pipes. Every time I get the pipes hot enough to braze, the oil boils and forms a pinhole leak in the joint.

Answer:

By Bob Henson

J.W. Harris Co.

Cincinnati, OH

Oil contamination can be a problem in any brazing application. Oil reduces the braze or solder filler metal’s ability to wet and bond to the base metal. When heated it frequently burns, leaving a surface residue. Flux used with soldering and brazing filler metals is designed to remove surface oxide and protect the base metal from further oxidation during heating. Flux is not an effective oil or grease cleaner.

There is no specific recommendation short of cleaning the parts prior to brazing or soldering. Perhaps readers may have suggestions for coping with this in the field.

Low-Pressure Control

From Jose Guevara

Via E-Mail

In the past, I would use a low-pressure control to maintain temperature in an R-12, medium-temp walk-in cooler. I would set it for 14-psi cut-out, 34-psi cut-in. But if I use R-409A and I try to use a pressure-temperature chart, there are vapor pressures and liquid pressures. I am not sure which pressures to use to set my low-pressure control.

Can anyone explain which pressures I should use (vapor or liquid) and why?

Answer:

Gus Rolotti

Atofina Chemicals Inc.

Philadelphia, PA

Your question is interesting and practical. The way you calculate your cut-ins and cut-outs are similar with R-409A as you were doing with R-12.

First of all, you are dealing with the vapor side of the system. So when using the pressure-temperature charts, you need to use the numbers from the vapor column. The liquid-side numbers are provided in case you need to calculate subcooling on the liquid side.

Next, you need to consider the fact that R-409A has an evaporator glide of about 10°F. This means that your outlet temperature will be about 5° higher and your inlet will be 5° lower (half the glide). For R-12, a cut-in of 34 psig corresponds to a temperature of about 37° and a cut-out of 14 psig corresponds to 9°.

For R-409A, then, your outlet temperature should be 37 + 5 = 42° and 9 + 5 = 14°. Using the pressure-temperature chart (vapor column), look for the equivalent pressures of 42° and 14°, which are about 36 psig for the cut-in and 15 for the cut-out. Depending on your system, you may need to adjust your cut-in and cut-out pressures slightly down to match exactly the box temperatures you are trying to keep.

Troubleshooting

From Dominic

Via E-Mail

I am working on a Rheem commer-cial gas heat/cool packaged unit Model #RRGF-350150CKR. I am trying to get a troubleshooting guide. How can I get a copy?

Answer:

By Peter Powell

Service Hotline Editor

We passed along your request to the folks at Rheem at P.O. Box 17010, Fort Smith, AR 72917-7010 headquarters. Within a few days, they sent us a 132-page manual on 6.5- through 20-ton commercial gas-electric rooftop equipment. In turn, the manual is being sent to you.

Readers (especially those with precise information needs on equipment) can probably secure the assistance they need by contacting manufacturers directly who, as indicated above, are more than willing to help. If you are unsure of an up-to-date address or phone number for a manufacturer, contact your local supply house or check The News’ HVACR Directory & Source Guide, which you receive at the start of the year as part of your subscription.

Publicationn date: 06/04/2001