Garage furnace runs for 20 min, stops, won't restart

Hello, I've spent 2 hours reading the last month's worth of posts to see if my question was answered already (and trying more than a few of the tips offered), and I'm sad to say my problem seems to be unique.

I have an approximately 15 year old furnace in my garage that was from an insurance salvage house; it does not have either original front door (burner/blower), but I'm pretty sure it is in the Carrier Family of appliances. Control board is United Technologies HK42FZ011, Product/Model # 395CAV042091AGJA. Only other name on plaque is BDP Co., Indianapolis, IN. Garage is detached, 2x4 construction with R-11 in the walls and R-5 in the ceiling. I live in the Twin Cities, MN and the current outside temperatures are ranging from -10F to 20F (night/day). The furnace is Natural Gas and testing today with a homemade manometer revealed 12.5" of watercolumn pressure at the valve in the garage (36" away from furnace gas valve assembly). I use an ancient Honeywell "donut" type dial thermostat mounted to the wall approx. 10 feet away from the furnace. The air intake has a 2"x16"x25" filter on it and the air outlet ducts into two 8" diameter pipes which travel up 4 feet and then into 90deg elbows for direct blasting into the garage. Good details?

Anyways, my problems started 2 weeks ago; on Thursday the furnace worked fine - just as it has for the last 6 years. Then, on Friday, I went to turn it on and it ran for 5 minutes (total run time varies from 5-20 minutes each day), shut off and attempted to restart 3 times and failed - going into lockout mode while flashing LED code 14. Turning the power on and off had no effect.

When it fails, the blower keeps running but the draft inducer motor stops. Then the draft inducer motor will start back up, the HSI will glow, the gas will flow & ignite, burn for 1 second (enveloping the Flame Sensor in the process) and then the gas stops and the whole process starts 2 more times. Nothing I've done has been able to get the system to run for more than a second once the unit has heated up to about 45 degrees. And I don't believe it's overheating since i can briefly put my hand on pretty much any surface inside the furnace (short of the burners themselves) and NOT burn myself.

So, in the last 2 weeks, I've: tested my gas pressure (12.5"wc), bypassed the highlimit & rollout & door & pressure switches to test them, tested continuity of those swtiches, physically removed the pressure switch and tested it (by sucking on the hose), replaced the pressure switch hose, removed/cleaned all grounds, removed/sanded the flame sensor (i was SO hoping this was the problem), checked EVERY electrical connection, removed the circuit board and checked for blown/burned diodes/resistors/caps/solder traces (none), sanded & re-crimped all electrical connectors and applied dielectric grease, shorted the thermostat terminals to eliminate the Honeywell as a problem, checked the 24vac fuse (duh), measured 26vac at the transformer and switches, removed the gas valve assembly and redoped the connection, blew burner orifices out while gas tube was disassembled, tested gas valves with 24vac (both click), and checked my outside vent for ice obstruction. Whew! You wanted detail, you got it!

So, anything i missed, or any suggestions, PLEASE HELP! I would very much like to get this running again since if it can run for 20 minutes tonight, I don't see how it can be "shot" or "totally broken" and would like to save my money when it's most likely something simple that I'm just not seeing.

Thanks!

 

This is a Carrier 80% furnace --- BDP stands for the other Carrier brands, Bryant, Day & Night and Payne.

The 1-4 diagnostic code is for flame failure, so the circuit board is not detecting that the main burner is lighting.

If you have a multimeter, check for the DC micro amps (uamps) flowing from the flame sensor wire back to the circuit board. There should be a minimum of .5 uamps, with 4-5 micro amps being a good reading.

I believe there should be a green wire grounding the circuit board to the furnace chassis --- check to be sure that is properly connected.

If all that's working, you have a bad circuit board you will need to replace.

This is one of the older 395CAV furnaces, and I would have thought it had a circuit board that had a lot of individual wire connections to it and no multiple plug assemblies. But I don't recognize the circuit board part number you gave, so perhaps it has those multiple plugs which makes it pretty straight forward to replace.

 

Also you want to measure the AC voltage on the flame sensor wire going back to the circuit board while the ignition cycle is going. Use one multimeter contact on the wire and the other to ground (chassis or G on the circuit board).

 

I finally got out there and clipped the ends off of the ground wires (bad crimps?) and crimped new connectors onto the wires. Then I flipped the switch...with the furnace beginning it's heat cycle, the flame sensor has 102vac (NOT 120vac) on it. I stopped the system then and wired my DMM inline between the flame sensor and the circuit board. My DMM's lowest setting though is only 200mA, so I wasn't surprised when it didn't register any amperage across it (either AC or DC). BUT, the furnace ran for 2 minutes with the DMM inline; it didn't shut off until I turned the thermostat from "HEAT" to "OFF" - I didn't want to leave my DMM inline any longer than necessary.

After returning all the wiring to standard, I flipped the switch back to "HEAT" and the system started - and failed to light (well, "run"...it did light for the 1 second for 3 times). Normally the internals get a little warm before they refuse to light, now it did it while still cold.


Hmmm...it's looking like the circuit board has an intermittent glitch, right? And with replacement boards being about $150 and a White-Rodgers universal replacement board being borderline cheaper at $120, I'm looking at 3 options:

1) buy the replacement board, hope it solves my problems and have $150 into a 15 year old furnace.

2) go out and buy a used furnace for $100-$350 and hope it works reliably for several years down the line. (the $350 model is another Carrier whose owner claims "it was only used one year"...um..."Caveat emptor!")

3) go out and spend $600 on a brand-new warrantied 80% Goodman furnace, install it in the garage until spring and then swap it into the house in the spring. (house has a 25+ year old Carrier 58SS with charring on the front, but it WORKS! lol )

Comments?

 

200mA setting on the meter? If so, that would mean it will register from 0 - 200, I do believe.

 

Yabbut --- one milliamp = 1,000 microamps, so I wouldn't expect much of a bump.

 

Hello nbb,


I'm not much for guessing about problems when there are tests you can do to check and be sure. I'd be looking at borrowing or buying a reasonable quality multimeter wer I you. Of course I'm not.

Another test you can do with your existing multimeter is to measure the AC voltage present from ground to the flame sensor wire when it's disconnected and the furnace is attempting it's ignition cycle. Typically you'd get 24 VAC or so--- if it's zero the circuit board is bad.

Putting $150 in this furnace to fix it sounds like a bargain to me ---especially compared to installing a new or replacement furnace.

 

been busy the last few days...but I did manage to order a new Fieldpiece LT-17 kit to measure microamps. Not that my current DMM is junk (it was top of the line when new)...it just appears that measuring microamps is a fairly HVAC-centric feature... anyways, gotta wait for that to ship/arrive now. Thanks for the help, everyone!

also, when you say in your last post to test Flame Sensor voltage again during the ignition cycle, should it really change from my previous reading of 102vac to the lower voltage? Those would seem to logically be separate circuits - high and low voltage.

 

The voltage on the flame sensor can vary depending on furnace design. Some are 24 VAC, others a higher voltage (which is better). With some the voltage may be on all the time, others only when the burners are supposed to be lit.

If you got no AC voltage at all, that would suggest that the ignition module is defective and you wouldn't need to measure the uamps. It's also a useful double check on a problem.

See how we try to make things easy for you?

 

The flame sensor wire has 102vac at all times when there is a call for heat.

 

The 102 VAC reading may well be normal for the furnace. I'd say you'll have to wait until you get your new multimeter and can measure the uamps on the flame rectification circuit.

 

Measured the flame circuit with my new DMM tonight. 5.5 to 7.0 microamps the whole time. it started at 5.0, quickly climbed to 5.5 then gradually climbed up to 7.0 over about 5-7 minutes - until the flames just stopped and it started cycling again. okay, Flame sensor is good.

I decided then (for some stupid reason) to test the gas valve for voltage while it cycles...without switching the test leads. D'oh! So....I have to go pick up a 0.5 A fuse at RatShak tomorrow since I blew the one in the new DMM.

anyways, what i did manage to test pretty much confirms that the Flame Sensor is good...and most likely that the circuit board is bad. but i still am curious why it works when COLD, but not after being used - for varying amounts of time. something in a circuit board relay, resistor, cap, diode or IC that heats up from the current going thru it during that initial heat up time until all of a sudden a path opens and the system fails? arghh...i hate electrical gremlins.

 

Yep, I'd say you need a new board.

And in my opinion, replacing the board is the smart decision over the other options you mentioned.

Remember, by replacing the board you have **new** electronics for many different functions in the furnace.

And a 395 CAV furnace is good equipment in my experience.

The only reasons I'd change it out would be 1) a choice to upgrade to a 90% efficient condensing furnace or 2) a cracked heat exchanger.

 

Seems the HK42FZ011 boards are a known problem:
Bulletin United Carrier Corporation Technologies Carrier Residential Engineering SMB 96-0023 Subject: FURNACE CONTROL BOARD RESISTOR SOLDER JOINT FAILURES 04/17/96 UNITS AFFECTED: CAC: 58MXA, 58MCA, 58WAV, 58PAV, 58RAV BDP: 350MAV, 340MAV, 395CAV, 376CAV, 383KAV, 373LAV PAYNE: 480BAV, 481BAV, 490AAV Resco/Eventemp/Cobra: GB1AAV, GB3AAV SITUATION: A resistor solder joint failure mode has been identified on the following control boards used in the subject gas furnace. Affected Controls: HK42FZ004 (Obsolete) HK42FZ007 (Obsolete) HK42FZ008 (RCD Replacement) HK42FZ009 (Production, Open faced control board) HK42FZ011 (Production, Covered control board) Refer to Table 1 for the affected serial number ranges of the subject units. Table 1 CAC MODELS SERIAL NO. RANGE BDB MODELS SERIAL NO. RANGE 58MCA 3193A - 4595A 340MAV 3193A - 4595A 58MXA 3193A - 4595A 350MAV 3193A - 4595A 58PAV 1594A - 4595A 383KAV 1594A - 4595A 58RAV 1594A - 4595A 373LAV 1594A - 4595A 58WAV 1594A - 4595A 395CAV 1594A - 4595A 58ZAV 1594A - 4595A 376CAV 1594A - 4595A PAYNE MODELS SERIAL NO. RANGE RESCO/EVENTEMP SERIAL NO. RANGE /COBRA 480BAV 1594A - 4595A GB1AAV 1594A - 4595A 481BAV 1594A - 4595A GB3AAV 1594A - 4595A For further information on replacing these controls please contact your supplier.