How To Repair Your Maple/Chase 9600 or Robertshaw 9600 Programmable Thermostat
If you have a thermostat that looks
like the image below, and it's not working, read on. This page may help
you fix the problem and get your thermostat working again. An owner's manual and product brief are also available here!
But first, a little introduction (skip this).
In 1995, my parents took a big step in modernizing their big old two
story house. They opted to install central air conditioning, and to do
this, the big old Lennox Aire-Flow (which began life as an oil burner
and later was converted to natural gas) furnace had to come out. There
simply wasn't any more room to add a set of air conditioning coils*.
And that old furnace was wearing out, showing signs of strange behavior
as it aged. Other than that, though, it was a thing to behold. And it
filled most of the front yard when it was cut up and taken out of
The new furnace and air conditioner
were both of the Comfortmaker brand, with the furnace being an RPJ-II
90% efficient unit and the air conditioner being rated as a 3-ton unit.
(Comfortmaker then was a brand of Inter-City Products in Lavergne,
Tennessee. Today it is part of the Carrier family.)
Anyway, with this new furnace came a
new thermostat to replace the old Honeywell "round" heat-only unit.
This new thermostat was a Maple/Chase brand, model 9600. I never
liked it that much. It didn't seem to be particularly accurate at the
best of times. And in 2003 or so, it stopped working reliably. You
could turn it to cool in the summer and you'd either be ignored, or the
air conditioning would stop turning on at some point. There never
seemed to by any rhyme or reason to it, so we changed the batteries and
found no improvement. Eventually, a Honeywell Magic Stat replaced it
and solved all the problems.
As I have long ago learned my lesson
about throwing things away **, the old thermostat got set aside for
future examination into why it broke. When working properly, this
thermostat has an audible indication that it has turned on. A relay
inside clicks noticeably whether in heat or A/C mode. So if you don't
hear the furnace come on, you can at least hear the thermostat signal
it to come on. When it was malfunctioning, this never happened. It was
worse with this thermostat when in cooling mode. Heating almost never
failed to work. And as was the case with so many things, hitting the
thermostat would usually convince it that we meant business and to
please turn the A/C or heat on now, thank you so very much.
Amazingly, you can (as of 2009) still
buy the 9600 thermostat from Robertshaw. If by some chance you need the
owner's manual, I have it here. You can also look at the product brief. Maple/Chase is now known as Invensys Controls.
I built something a while ago using
another programmable thermostat (located in a different house) to
operate a room air conditioner based on what the thermostat said to do.
That air conditioner had been saved from the curb and hot wired to work
around a bad thermostat. This worked well, the parts to make it work
were for the most part given to me, and I kind of wanted to build
another one for the air conditioner on the lower floor of that house.
(This had proven much more accurate than the thermostat built into the
To build another one, I'd need
another thermostat, 24 volt transformer and a contactor. And like I
said, the first time around, these were given to me. I'd been pricing
programmable thermostats and found them more expensive than I wanted
them to be. So when the idea hit me to build another one of these
contraptions, I turned to the Maple/Chase thermostat that had been
retired so many years ago. (It is June of 2009 as I write this.)
(I also saw this post
on the AskMeHelpDesk site from someone who had two of these that
wouldn't power on their heating or cooling systems. So this person--if,
two years later, they are still looking for a fix--can find that fix
New batteries were put into place and
the thermostat still didn't work any better. In fact, it was easily
worse off than it had been. I couldn't get either the heat or A/C modes
to engage the relay. So I got to looking, and I found that the problem
was in the mode (cool/off/heat) switch. You need to take the cover off
of the thermostat to see the workings of this switch. Fortunately,
that's easy to do. All you need is a quarter.
When you get the cover off, you can see the circuit board inside.
At this point, you probably need to
take your thermostat off the wall. Do that now, making a careful note
of where the wires are connected. You will need to put them back after
the repair. You might also wish to unscrew the fuse or turn off the
circuit breaker leading to your furnace. If your furnace has a switch
located nearby, you can also use it.
What we're interested in examining is
the mode switch, which is covered up by a molded piece of plastic that
is the "exposed" part of the switch you see when the cover is on. This
piece lifts up and off to reveal the real switch.
There are actually two switches. And
while both may require treatment to restore the thermostat to working
order, it is the bottom one that is the most important. The bottom
switch is the one that actually engages the cooling or heating mode of
the thermostat and allows the relay to be turned on, thusly completing
the circuit and telling the A/C or furnace to start.
The problem is that these switches
are open bodied. Air can get at them, and this causes the copper
contacts to turn dark or corrode. When that happens, your thermostat
stops working properly. What we're going to do here is clean the
switches. Fortunately, their open design makes this easy. But that's
about the best you can hope for. While it would in theory be possible
to take the top covers off of the switches--carefully setting aside the
pieces so they don't get lost--they are too close together on the board
to let you do this. (Particularly industrious people could desolder the
switches and do as they pleased with them. I didn't feel like doing
There are some other things in the way as well. These can be removed and will your make your job easier if you do so.
This thing gets in the way of what
you want to do, so it should be removed. The good news is that you can
do so pretty easily. First, you need to remove the batteries from your thermostat and realize that the components on the board are sensitive to electro-static discharge. Touch
the case of a grounded object and stay put after you get started. What
you're going to do involves several steps, but it isn't hard and can be
done in about an hour if you take your time. However, you can damage
the thermostat irreparably by handling it roughly, zapping it or being
abusive when you take it apart.
To get it out, you need to remove the
circuit board as it is fastened from behind. There are three screws
holding the board in place. One and two are located at the lower left
and lower right corners of the board. The third is located above the
display shroud. Remove them, and set them aside where they won't roll
Turn the circuit board over, being careful of the two exposed battery holder contacts.
You're almost ready to remove the
display shroud and buttons. However, there are some things to consider
before you start. The first is the thermal sensor. The soldering on my
thermostat was of poor quality, and if you break this item, your
thermostat won't even work at all because it can't sense the room
temperature. Be careful and try to avoid touching it too much.
There is also the display (on the other side of the board). This is a glass
LCD and it is connected to the circuit board using "zebra stripe"
connections. While mine appeared to be held firmly in place, there is
no guarantee of this being the case with yours. And if you break the
display, you will have a thermostat that is hard to use. Should the
display come off, it can be realigned, although doing so is sometimes a
pain and requires multiple attempts before it is right.
Once you have removed the screws, you
cannot just remove the buttons and shroud. There are two plastic pegs
protruding through the circuit board that are still holding the module
in place. Cup your other hand over the display and buttons (on the
other side of the board) and use a finger from your free hand to push
the pegs through the board. The shroud will now come out and now you
can do what needs to be done.
Position the circuit board so that
the pushbuttons below the display are closest to you. Push both the
switches all the way over to the heat position, so that they are in the
furthest position away from you.
You can now see the little copper
"pillows" that make the switches work. Chances are they will be
somewhat green or even black looking. To clean them, use a small
(SMALL!) file or flat bladed screwdriver to GENTLY
scrape the residue off. Don't bang the file or screwdriver madly around
inside the switch as you will surely break it. Just do a slow and
gentle job of scraping the gunk off of the contacts. You should be able
to get back to shiny copper once again.
When you're satisifed, flip the
circuit board around, slide both slides over to COOL (so that again,
they are far away from you) and clean those contacts.
Now you'd done just about the best you can do to clean these contacts.
There is one more switch you should
pay attention to, and that is the fan switch. I found that the fan
switch--despite hardly being used on my thermostat--was in even worse
condition than the two main switches. Perhaps the somewhat regular use
of the main switches kept them from getting to be in such bad shape.
The fan switch, being by itself, can be gently eased open (taking care
to avoid losing any of the insides once again) or you can clean it just
like you did the two main switches.
How To Keep This From Happening Again
Ideally, now that you've solved the
problem, you would want to keep it from happening again--or, at the
very least, making sure the life of the thermostat is prolonged for
quite a few more years.
The way to do this is to put
electrical anti-oxidation compound on the contact surfaces of all these
switches. You can buy this at any hardware store or electrical supply
house and it's not expensive. Put some of it on a toothpick or cotton
swab, and put it on the switch contacts. You don't have to go
overboard. Just use enough to cover the contacts and make sure they
stay that way. Work the switch a few times to be sure you've got enough
in there, and that it isn't leaving the contacts unprotected as the
switch moves around when operated.
Put The Thermostat Back Together
Assembly is pretty much the reverse
of disassembly. Put the display shroud and buttons in place, making
sure to push the pegs back through the board. Fasten those screws into
place, and set the circuit board back into the rear half of the
cabinet. Be sure the battery terminals have gone into the right places
and don't force anything! Once the circuit board is in place, fasten it
using the three screws removed earlier. Re-insert the batteries and the
thermostat's display should come on immediately. It will start
displaying the room temperature in seconds, and will become more
correct in the next few minutes.
Test The Thermostat
Now you need to test the switches to
make sure they're really working. You want to turn the switch from cool
or heat to OFF several tiems, and verify that you hear a relay click
each time. This is easy enough to do for heating. Set the temperature
so it reads warmer than the current room temperature reported by the
thermostat and slide the switch to HEAT. You should hear a click each
time you do this from inside the thermostat.
Cooling is a little more difficult to
test. You do the opposite of heating--slide the switch to cool and turn
the temperature down BELOW room temperature. The relay should click.
However, the thermostat's controller has compressor protection built in
and won't immediately cycle the relay back on if you turn the switch to
OFF and then COOL again.
Fortunately, there is a way around
this. Inside the thermostat and next to the TEMPERATURE DOWN button is
an unlabeled black button that has no control poking through the front
panel. This is a reset button that blows away the entire contents of
your thermostat's memory--including the amount of time since the COOL
mode was last selected. So, press RESET, lower the temperature below
room or indicated temp and turn the mode switch to COOL. Repeat this a
few times with the RESET button and there you have it.
do this with the thermostat hooked up to a cooling system. You could
cause expensive damage and will at the very least put more wear and
tear on your cooling system than you should. The same is probably true
of heating--you should not sit there and cycle the thermostat
repeatedly if it's actually hooked up to a working heating system.
Questions or Comments? Please Write!
2008-09 William R.
Walsh. All Rights Reserved. Last Updated 06/21/2009. Permission is granted to mirror this page
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* An old-school furnace repair man and plumber suggested that the A/C
coils could have been situated in the air intake of the old Aire-Flow
furnace, instead of trying to place them over the top of the output
plenum. He was probably right, but it was doubtlessly an improvement to
go from a furnace that was probably 60-65% efficient at best to go to
one that is 90% efficient.
** I have learned long ago (and come to accept for the most part) that
I should never throw anything away, because I never know when I might
need it, or a part of it. The same is also true of valuable items that
are given to me with missing parts. I know that as long as I have the
item in question, I will never get the missing parts. But if throw it
away, the missing parts that I would have needed with show up almost