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Friday, December 22, 2017

P0141 Replacing the oxygen sensor in 2007 Honda Accord EX 2.4L

There is lots of videos and help around the net for this one, but maybe details of my experience will help someone because there are a couple twists.   This job is something that an average person with a good sense of humor can do.  It is an exercise in inconvenience but not mechanically complex.   It doesn't take any more tools than a socket wrench and a jack stand.  You do need a cheap tool to remove the sensor that you can buy when you buy the sensor.

Check engine light comes on.    Within a day I get the notice for my bi-yearly emissions inspection.  Life is like this sometimes.    Need to fix it today.   You can see i also need an oil change.

 My 20 year old OBD reader (can get the auto parts store to do this for you also) says P0141 Faulty Heated Oxygen Sensor (H2OS) Bank 1 Sensor 2.   Number 2 means the sensor on the catalytic converter under the car, not the one on the exhaust manifold under the hood.   My car is a 2007 Honda Accord EX 2.4L 4 Cylinder.

This could be due to bad wires, but most likely the O2 sensor is just bad, this car is 10 years old now.
You can look under the car and see this thing on the side of the catalytic converter.    I didn't do any diagnosis, i just replaced the sensor.

These are not too expensive, used to be a lot more.  I bought this one for $26.

You also need a special socket wrench.  I understand that auto parts stores may lend you one for a deposit, but they are only a couple bucks if you buy a cheap one, and this was the cheapest and worked just fine.

Parts came quickly.   The sensor has a long wire that runs through some clips and eventually has a grommet in the floor of the car under the passenger's seat.  Nuts!   It is under a flap of carpet that you could possibly access by pushing the seat all the way up and reaching under but removing the seat is actually very easy and makes this job less of pain.  The wire plugs in to a connector under the seat.

Do your self a favor and remove the seat as the first step.  Just take out the four bolts, two in front and two in rear under some plastic covers that snap off and back on.   Bolts come out easily with a socket wrench and the seat lifts up and you can reach the connector.

Unplug it and push the grommet and wire through the hole in the floor.   Here it is hanging out the bottom of the car now.

I'm not a fan of being crushed under my car, so i jacked up the front right wheel and put a jack stand under it, next to the jack.  I chocked the two rear wheels and pulled the emergency brake.   That created just enough room to get under and do the deed.   Still very awkward.

Reached under, put on the socket tool ,attached a socket wrench, wiggled and pushed and sensor was stuck tight.  I took a small sledge hammer and hit the socket wrench a few times.   Not an easy task while reaching under the car.  Eventually it budged and I could use the socket and wrench to remove the sensor.  Touch and go there for a while.  I knocked a lot of rust off the cat in the process.  My heat shields were already attached by some big hose clamps from home depot because they had come loose years ago.

The white plastic clips come off with a little pry from a screwdriver.  I removed the old cable from the clips.

Installed the new sensor with the wrench.  Routed the cable through the clips and pushed it and the grommet up through the hole in the floor.

From inside the car i connected the cable and pushed the grommet into place.

Reattached the seat without any issue, lowered the car.   Here is where the fun part begins!

Started up the car just fine, and the check engine light is still on.   Read the codes and it still says P0141.  Played around a bit starting the car and reading it.    Check engine light is still on and code persists.  Looks like I need to reset the code.  My old reader won't erase the code, it just says Err when i press and hold erase.   Dang.  Tried many times.  Can't reset the code.

I decide to take it to the local auto supply store and get them to reset it.   They tell me they aren't allowed to do a reset.   Some posts say you can ask them to push the button yourself, but i didn't try that.   I get frustrated and go buy myself lunch.

I need to get the car emission tested and I have to clear that light TODAY.  While eating lunch and reading on the web I see I can disconnect the battery and press the horn to drain all the charge as an alternative to erasing the code with an OBD reader.  However I'm out to lunch with no tools.   But when i get back in the car WooT!  The code has disappeared by itself.  Problem solved.  It just needed some driving and a few more starts to clear the fault code.

I drive immediately to the emissions inspection station and get it tested.  It passed!  Hooray.   A big win.

Tuesday, September 5, 2017

Heat pump inside air handler coils frozen

Didn't expect my blog to become an HVAC repair guide, but life brings what it wants to.

My rental house full of young "adults" and I get the call the AC isn't working on a warm day.

They say the inside unit is running, air is blowing, and the fan outside on the heat pump condenser is also running normally.  But it is still warm.   Is it low freon or a blown compressor?  I hope not, that will blow months of rent money earned.

I go check it out and there is moisture on the unit and floor, it is sweaty and the insulated freon pipe to the outside is all sweaty and dripping, even icy in spots.

The air filter is sopping wet and wont come out, it seems stuck in the unit and too soggy to pull out.

I take off the cover of the air handler inside (the lower one) and instantly see the issue.   The whole coil is a humongous block of ice.   Wish i took a picture.  A little quizzing of the occupants and I get an admission that somebody turned the AC down to 60 because they were hot.

It's possible that there is low freon, but i'm betting this is user error.   I left them with the fan running and the AC unit off, telling them it will be 2 days to melt that mess.  Luckily it is only 80 today and supposed to be cooler tomorrow.

Went back after three days, luckily the weather was cool so the lack of A/C didn't get any complaints.  I replaced the filter and checked the coil.  All back to normal.  Turned on the A/C and it worked fine and cooled normally.  No harm done.  Whew.

Thursday, April 20, 2017

Heat pump won't cool, condenser outside clicking and won't run

Not a lot of pictures here because i didn't think this fix would be the epic that it was.
The system is a generic International Comfort Products.   Inside the box I found that Trane, Tempstar, Heil and ICP units use a lot of the same parts.  So pretty much ignore the brand name on the unit.

First hot day in a while and the wife switches the heat pump to cooling mode and when I get home she complains it is not cooling.

Quick inspection reveals warm air blowing and the outside unit - condenser - is not running when the thermostat says it is cooling.   The strangest thing is the condenser outside is quiet except for a fairly loud clicking about once every 2-3 seconds.

The solution was that the solenoid for the reversing valve (inside the outside condenser) was bad.  It was shorted out.   Replacing it is easy and can be done by opening the unit and removing one nut and plugging in the wires.  Cost was less than $15 and can be done with only a socket wrench.

Here is how i figured it out...  I bit of a comedy of errors but I got there in the end.

Google searching doesn't help. So i decide to start swapping parts.

I open the access panel on the outside of the condenser.   With my finger feeling i discover that one of the relays on the control board is doing the clicking.   My voltmeter shows the unit is getting both 240V and 24V power.   The contactor (big relay) coil is not powered, so something is not telling the unit to start.

I decided the control board might be broken and ordered one on ebay for $20.
Heil Tempstar Defrost Control Board 1087952 CEPL130547-01 CEBD430547-02A

Picture of the contactor on the left, and the control board on the right.

When the control board came a few days later i swapped it in.  all the connections are pull off and plug back in.  just transfer the wires one by one.

All done, i go to turn it on and I find the thermostat is BLANK.   Measuring the voltage at the green/red thermostat wires after pulling off the thermostat from the wall, i find i have no 24V anymore.   At the condenser no 24V either.   Whaaa?  It was there before.  I either blew the transformer or something else did in the 4 days since I tested before.   

Upstairs in the attic I open the panel on the air handler.  The transformer is in the back in the lower right.  No 24V on it's output.  Remove it and find that the primary coil measures open. 

I buy one on ebay for $11.99

Comfortmaker Heil Tempstar 24v Repacement Relay Contactor 1050699 HQ1050699HW

When transformer comes I swap it in.  Now I have 24V power.  Thermostat is working again.   Outside the condenser is clicking again.  A week with out cooling and a total fail.  I'm right where I started.   It was not the control board.

At this point I got lucky.  I played with the thermostat and I find that the unit will heat, but not cool.  In heat mode the condenser starts right up and heat pours out.  That is the big clue.  Googling heat and no cool problem I find quickly that the reversing valve is likely the issue.   The reversing valve switches the direction of flow of coolant.

Reversing valve is inside the the outside unit.  I have to take the top off with the fan and reach down.   The reversing valve looks like this. I didn't take a real picture, this is generic picture.   On top is the solenoid.   When I disconnected the wires from it, the clicking stopped.
I measured the voltage at the solenoid and it was getting 24V.   There was no magnetic field from the soldenoid (put a screwdriver near it and it should be attracted) and resistance was about 1.5 ohms.  It should be 10-60 ohms.   The solenoid part (blue in this picture, but red in my unit) comes right out by removing the nut you see on the side.

I ordered a new one for $12.75.  
Trane American Standard Heat Pump Reversing Valve Solenoid Coil COL05901

When new solenoid came I swapped it in and everything worked! It took nearly two weeks waiting for three parts in a row but at least i saved a lot of money despite my bumbling.

After thinking about this repair I think the 24V transformer was the root cause of blowing the reversing valve solenoid.   The PRIMARY of the transformer was open when it was blown, which makes no sense that I blew it swapping parts.  Perhaps the 24V over voltaged the solenoid and blew it.   So that makes me feel better, i replaced the bad transformer in the process.