Bathroom Space Heater Repair

Our upstairs bathroom has no heat — no ducts run there — so we have a small electric wall-mounted space heater for cold winter months. We already replaced it once, as the Cadet Company in Washington State issued a recall on it. But that was 20 years ago.

In general it was still working fine, but during the most recent winter it started to come on by itself in the middle of the night, first on colder nights, and as the winter went on, even when it was not so cold. I became concerned that this thing would end up on continuously when we were out of town, overheat, and burn the place down.

Note that the heater does not really have an off switch per se. All it has is a temperature dial, and up until now, turning it to 0 was basically the same as off. But not anymore.

At first, I thought about just replacing it. I spent a lot of time searching around HomeDepot.com and so on, but couldn’t find one that I liked better. Giving up for now, I thought I’d pull the thing out and see if it was just some dirty contacts on the thermostat or something.

So, I turned off the breaker, pulled it from the wall, and expected a filthy dust-ridden nightmare.

Turns out, not so much. There was some dust, but the airflow must keep it pretty clean. I cleaned up what I could, then moved to the issue at hand.

First, how does this work? The only electrical parts in this thing are:

  • heating coil
  • fan
  • temperature control
  • over-temperature thermal fuse

The fan still runs. The coil still heats. The over-temperature thermal fuse is a one time, non-resettable device that blows when a severe over-temperature condition exists. Since the heater does still make heat, I figure it must still be OK.

The temperature control looks pretty simple:

I tried to get a picture from the side, to show how it works. This is not that picture, alas:

Basically, this thing is a micro-switch, a knob, a bimetallic strip, and a set screw. When the temperature goes down, the strip bends and pushes on the switch, turning on the heater. The set point is determined overall by the knob — it deflects in or out the strip.

But the key to my problem is the set screw, it turns out. This puts a minimum mechanical bias on the strip, so it either is on constantly, or, as you turn it further, requires the knob to be further and further from the off position before the heater will come on.

In the end, I could have fixed this without removing the unit from the wall. Oh well. At least now I know!

Bosch Dishwasher Repair

Unfortunately I didn’t take any photos… all I have left of the repair are fading memories, an email for the replacement part in January 2015, and a working dishwasher.

One day our 20 year old dishwasher ran dry. Literally. No water was entering, though it pretended to go through the motions.

I figured there must be some inlet valve that broke. Time to take a look.

I removed the one remaining loose screw holding the washer into the cabinet, and slid it forward. Clearly, all the good stuff is on the back and bottom sides, so I had to pull it completely out, and actually flip it over on its top.

I traced the route of water into the machine and found the inlet valve. I unplugged the spade plugs going to it, disconnected the water inlet and outlet connections, and took it down to the workbench.

I tried applying 120v AC to the terminals, and nothing happened — no clicking, nada. So, time to get a replacement.

Unfortunately, my usual go-to site for replacement parts, RepairClinic.com, did not have it. But, I found it on Sears Parts Direct.

After ordering the part and waiting a few days, it was easy enough to connect it in place of the old one, flip the dishwasher back over, and slide it into the cabinet. I took this as an opportunity to adjust the leg height and install two new mounting screws, so it’s no longer a bit wobbly. A quick test showed that the unit worked again. Hurray for our team!

Zenn Instrument Cluster Repair

I have a 2007 Zenn NEV (neighborhood electric vehicle) by Feel Good Cars / ZENN Motor Company. This small car was one of the very first mass-produced electric vehicles available in the US, that was not truly a suped-up golf cart. However, having shipped in low volumes and eventually going out of business, the car is not without some major flaws. One of the most common to fail, and expensive to repair, is the speedometer / odometer / battery level display, what Zenn calls the Instrument Cluster. When mine started to fail, it at first seemed to be related to moisture. My car has another common flaw, a leaky roof due to a failure of the glue that holds down the roof panel. After using a dehumidifier to dry out the car, I noticed the display started working again. However, this cure did not last for long, and later attempts to fix the display failures did not succeed.

Come the fall of 2014, I decided to finally sell the car. But what to do? The display didn’t work, and a new one would be $800. I had considered trying to take the module out of the car to troubleshoot it in the past, but it was clear it was a major undertaking. First, one was instructed in the service manual to remove the dash. Yikes! So that held me back for a bit. Eventually I decided to go for it. It turns out, one does not need to completely remove the dash. I did the following to remove the module (this goes with the instructions on pages 32-33 of the service manual):

  1. did not remove the steering wheel (really did not want to do that!)
  2. removed the side view mirrors, as the panels inside the pillars block the dash board from being lifted away
  3. removed the panel where the heating controls are, but I don’t think this was necessary
  4. did not disconnect the speakers (the instructions say to remove them, but since I was trying to keep it simple and not remove the whole dash, I left them in)
  5. removed the lower black plastic retaining rivet from the instrument panel (the lower part, by the light)
  6. removed the 2 left and right black plastic retaining rivets from the instrument panel
  7. removed the 2 left and right square head screws below the HVAC vents
  8. did not disconnect the heating throttle switch on the housing diffuser (looked difficult and unnecessary)
  9. removed the screws that hold the instrument cluster in
  10. started pulling the dashboard loose, just enough on the passenger side to get the instrument cluster out (I had to disconnect the passenger side fan duct)
  11. (the hard part)reached in through the hole in the dash where the instrument cluster mounts, around the back side of the now-loose instrument cluster, and disconnected the two cables
  12. pulled out the instrument cluster through the hole (by loosening the dash board, there is enough room to maneuver the instrument cluster to get it out)

Dash loosened, cluster removed

Next, I took the cluster to my workbench, and inspected the circuit board very thoroughly.  Nothing appeared the slightest bit burned or damaged; none of the components or copper traces were dark, warped, or scorched.  Time to power it up.

Using the wiring diagrams in the service manual, I figured out how.  I luckily had on hand a number of unused pins for similar Molex-style connectors, and stuck 4 in the proper holes in connector J4.  In the photo below, you can see I wrote with a sharpie the pin numbers on the end with pins 22 and 11.  Pin 22 needs to be connected to ground, while pins 9, 10, and 11 need to be powered with +12volts DC.  I connected 9, 10, and 11 together with solder, but wire would work just as well.

Applying power to the cluster

The display now powered up, but, as expected, had random segments dark while others were powered.  It’s hard to make out the speed or distance if all of them are not on when they are supposed to be!  Poking around at the board, I discovered the flex cable that connects the display panel to the circuit board was the culprit.  Pressing it down against the glass caused some of the segments to come on.  Pressing down the whole width of the cable against the glass made the whole display appear to be correct.

Unfortunately, such a flex cable connection is hard to repair.  They are somehow soldered and glued at the factory, but not something I felt comfortable fixing.  I did try adding a bit of glue between the cable and the glass, but this was ineffective.

I decided the solution was to make a clamp out of brass that could just stay there forever, keeping pressure on the flex cable.  I put some tape between the brass and the flex cable so it didn’t damage the cable.  I used a strip of brass from the hardware store that was as wide as the flex cable, and cut and bent it to reach around the side of the instrument cluster and press against the circuit board connector on the opposite side.  It’s kind of a squared-off U shape.

Brass clamp holding flex cable against the glass display

Here’s a close up of the side pressing against the glass.  Unfortunately I didn’t take any pictures of what’s underneath — the flex cable glued to the glass.

Brass clamp and tape pressing against flex cable and glass

Here’s the other side, where the clamp grabs on.  It’s important to shape the brass such that it cannot possibly short out the flex cable connector pins.

Brass clamp grabbing on to the connector

Here’s another view.

Another view

Here’s proof the repair worked.  When you first power up the cluster, it tests the display by turning on all segments.  I captured this photo, showing all the critical segments are now lit.  There might be a couple on the lower left number that are still not fixed, but I’m not even sure what that section of the display is for.

All important segments are now lit

After a second or two, the normal display appears.

Normal display

A nice aspect of this repair is that, once the back cover is screwed on the instrument cluster, it just touches the brass clamp, ensuring it can’t come loose.

Rear cover attached

All that was left at this point was mounting it back in the dash and reassembling everything.

The hardest part of this was reaching in the hole on the dash and getting the cables reconnected.  Reattaching the passenger side HVAC vent was also a bit difficult, but doable.

Cables inside dash

Nice to have the display working again.  Too bad I got too busy at work after I did this repair in November to sell the car… hopefully I will do so soon.

 

 

Nest Smart Thermostat Troubles

A happy Nest is a warm nest

A happy Nest is a warm nest

This Christmas I received a Nest thermostat — pretty awesome step up in technology compared to the 1994 era Honeywell thermostat we were still using!

Ancient Honeywell thermostat

Ancient Honeywell thermostat

The instructions were very straightforward. Our old thermostat used 3 wires from the furnace — G, W, and R. G controls the fan, W controls the gas valve, and R is power. Missing, however, was a C or common connection — though the Nest is supposed to support systems that don’t have one.

All seemed to be well the first evening and night. My son and I configured it to connect to our wireless network, set the Nest’s various settings for heating type and so on, and installed apps on our phones and iPad.

The next morning, the heat came on for a few minutes, and then mysteriously stopped. I heard it try to turn on shortly thereafter, which resulted in a disconcerting series of repeating aborted heating cycles of a few seconds each (whoosh! click! whoosh! click! whoosh! click!). Time to investigate!

Searching their support forums turned up a likely culprit — the lack of a C connection.

Unlike the old Honeywell, which ran from a few AA cells for a few years at a time, the Nest has a non-replaceable internal battery, which it needs to keep charged somehow. If your thermostat wiring provides R and C (which basically tie to two sides of a 24 volt AC transformer in the furnace), then it uses those to keep the battery charged. Without C, the Nest has clever circuitry which is supposed to fake one using G and W as current return paths. Unfortunately, this bit of cleverness failed in my case, and the Nest did not work well.

Luckily, being pack-rats, we never throw anything away, including the manual for the furnace. A cursory glance turned up no C connection per se. However, after studying it for a while, it became clear that chassis ground and Earth ground were both tied to one side of the 24 volt transformer, and the R wire went to the other side. Bingo!

Furnace Schematic

Schematic for our old furnace

I turned off furnace power and took off the covers of the furnace, then traced the wires. This unveiled a ready-to-be-used blue wire running to chassis ground, right by the other wires connected to the thermostat cable. Luckily, that cable had a few unused wires, so I picked the brown one to run the new C line. I then connected it to the C terminal on the Nest, closed up the furnace, and turned furnace power back on. A quick inspection of the Nest wiring screen confirmed that the Nest automatically detected the new C line.

Inside the furnace

Inside the furnace

I tested the furnace a bunch of times that day, and the problem was solved. Phew.