Service Hotline: 10/07/2002


By Walt Thigpen
Bloomington, IL

How do I change the clock on my Maple Chase thermostat?

From Robert M. Rados
Technical Service Manager
Maple Chase
Downers Grove, IL

To change the time, day, differential, and residual cool settings on a Maple Chase or Robertshaw 9600 or 9700 Series thermostat, follow these steps.

1. Press and hold the SET button.

2. While holding the SET button, press and hold the PROG/MAN button.

3. Release both buttons simultaneously. The current time of day will now appear in the display window.

4. Use the CHANGE down and CHANGE up buttons to increase or decrease the time.

5. When the desired time is reached, press the SET button. The current day of the week will now appear in the display window.

6. Use the CHANGE down and CHANGE up buttons to increase or decrease the day.

7. When the desired day is reached, press the SET button. The current temperature differential will now appear in the display window.

8. Use the CHANGE down and CHANGE up buttons to increase or decrease the temperature differential.

9. When the desired temperature differential is reached, press the SET button. The display will either return back to the default screen or the setting for residual cool will appear in the display window (depending on the model).

10. Use the CHANGE down and CHANGE up buttons to increase or decrease the residual cool setting (fan delay after break in cool mode).

11. When the desired residual cool setting is reached, press the SET button. The display will now return to the default screen.

Note: The display will always return back to the default screen after 45 seconds has elapsed without pressing any buttons. Any changes made up to this point will be saved into memory.


By Tiffany Campbell
Via E-Mail

I am trying to find information regarding how long a vacuum should be put on lines to evacuate them properly before charging them with refrigerant. One HVAC contractor tells me at least 30 minutes. But another tells me that since the lines have nitrogen in them now, moisture isn’t a problem, so 10 to 15 minutes should be sufficient.

Do some gas furnaces have evaporator coils that are matched already for 10 or 12 SEER units? Would small tears in the outer layer of flexible ducting affect efficiency?

From Dan Kramer, P.E.
Specialist Grade Member of RSES
Professional Engineer

I don’t think evacuation time is a good measure for an evacuation procedure.

The primary purpose of evacuating is to remove moisture and non-condensibles such as air and nitrogen to find leaks.

Good practice requires that the pressure in the evacuated line be reduced to and maintained at a pressure of 500 microns for 20 or 30 minutes. To do this, you need a vacuum pump capable of reaching the desired low pressure and a micron gauge (not a compound gauge) that will correctly indicate the low pressure. The vacuum gauge must be connected directly to the system being evacuated, not to the vacuum pump or the hoses connecting the pump to the system.

Then, after the evacuation period at the correct 500-micron pressure, the vacuum pump should be valved off and the micron gauge monitored for at least five minutes to see if the pressure rises sharply.

A sharp rise could indicate either a leak or the presence of water not yet removed. For instance, if the system is at 60 degrees F, the equilibrium pressure of water is 13,000 microns. So free water will cause quite a jump in the pressure. If the rise is slow, then stops, it indicates a normal situation. If the pressure keeps rising slowly, it indicates a leak.

If the pump cannot lower the pressure to 500 microns, it suggests either a large leak, free water in the system, or a pump problem. You can check the pump by moving the micron gauge to the pump inlet and valving off the line to the system.

If there is water in the system or lines, you may have to run the vacuum for a longer period until the pressure does drop. If there is a leak, of course, you have to repair it.

Evaporator matching: The best way to find out whether a furnace unit you are interested in has an evaporator that matches any given compressor or condensing unit is to ask the furnace manufacturer.

Tears in the outer layer of flex: Flexible ducting may have foam insulation that is of an “open cell” or “closed cell” construction. Open cell insulation will allow water vapor to migrate to the inner duct and eventually saturate the insulation, making it ineffective for the purpose. Closed cell foam will allow moisture to migrate to the colder duct much more slowly.

However, you should ask yourself, “Just why did the duct manufacturer go to the expense of providing the outer duct covering if it wasn’t necessary?” I would carefully patch all insulation tears and would follow the flex manufacturer’s instructions for doing so.

Coil Cleaning

By TonelocT
E-Mail Address

An A.O. Smith furnace dating back to 1979 makes noise when I turn it up to 80 degrees F. A plumber last year told me the coil needed to be cleaned. The coils do look dirty, but not that dirty. I’m trying to find out if that is the true problem so I can buy some coil cleaner, or if it is something else.

From John Lawler
Director of Product Management

It is difficult to assess the problem in as much as it involves a noise from a furnace and a potentially dirty coil. However, you could use any reputable cleaner in cleaning the coil to see if the noise is affected. A person in your area with experience in servicing furnaces may also provide some assistance.

Publication date: 10/07/2002

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