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!

Maple Chase or Robershaw 9600 Thermostat

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 service.

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 air conditioner.)

The Repair

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 here.)

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.

Removing the thermostat cover. © Maple/Chase

When you get the cover off, you can see the circuit board inside.

Top of the thermostat's circuit board.

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.

Two Switches

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 that.)

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.

Display Shroud and Buttons

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 off.

Location of the circuit board retaining screws...

Turn the circuit board over, being careful of the two exposed battery holder contacts.

Backside of the circuit board

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.

Switches

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.

Fan Switch Contacts in bad condition

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.

Warning: NEVER 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.



Go Back>
Questions or Comments? Please Write!

Copyright © 2008-09 William R. Walsh. All Rights Reserved. Last Updated 06/21/2009. Permission is granted to mirror this page in its unedited entirety as long as a link back to this site and credit for the material is provided. You may not charge a fee or exchange items of value to provide access to this page or its content, other than an amount reasonably necessary to cover the cost of connection time, data transfer or printing supplies. Content from this page may not be displayed alongside advertising content of any type. You may use portions of this page in other products only if you provide credit and a link back to this page and only if the finished product is freely accessible to anyone interested in having a copy. If you use this material in work of your own, you may not charge or exchange items of value to provide access (other than as reasonably necessary to cover connection time, data transfer fees, or to cover printing supply costs) nor may you display advertising materials alongside any content you use from this page. Images may not be edited other than to resize them or to provide for faster downloading.

* 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 immediately afterwards.