York electric furnace control board - Relay questions

[smnmedic]

My furnace went out and it's a little cold in here to say the least. Luck has it they do not make this control board anymore, but I believe one of the relays are bad so I was going to start there. When i went to find a replacement relay no one has one in stock! It is a Potter and Brumfield  T90N1D42-22-01 30a 240vac relay. The coil voltage is 22v. There's plenty of T90N's with 24v and 18v coil voltages, but no 22v!

My first question is if I could use an 18v or 24v  relay instead? I was hoping they used the 22v because it was cheaper, but that an 18v or 24v would also work?

One of the first problems I ran into was that I couldn't find a schematic for the York control board. It's model# 031-01213-0000, 6EH20-1 Rev. B. If anyone happens to have a schematic for this board or can direct me to a copy is really appreciate it!

Since I don't have a schematic and I'm fairly new to electronics I'm lost. I'm able to read most of the resistor values and test them and some capacitors, but there are some components I have no idea what they are. I do know enough to cut off the mains and remove the board, which I have done, and do my testing outside the furnace but without a schematic it's complicated.

I did remove the relays from the board and test them. I used a power supply that was 19v from a laptop and connected it to the terminals of the relays. All of them worked but one appeared to have a delay. In any case, since I have the board out, I would prefer to replace all 5 of them. I'm hoping I can use an 18v or 24v, but if not maybe someone on here can direct me to a supplier that has them or to another brand of relays that have the same specifications?

I did download the specs for the relays and here's what they are:

T90 = relay series (30a Relay)
N = Open (optional dust cover)
1 = Form A / Normally open (does not have a common terminal)
D = DC voltage
4 = PCB terminals
2 = Contact material AgCd0
22 = Coil voltage

It is a single pole single throw relay with 4 terminals that are through holds soldered to the board.

Any help would be appreciated. Anything from ways to test the board without having to use high voltage to a replacement relay! I'm cold and stuck at the moment!

Thanks in advance!!!

[Armadillo]

24v version would also work, because the pull in voltage of typical relay is much lower and 22v definitely can pull-in. Just change the defective relay will do because your troubleshooting without the schematic may not be the FINAL.

[Ian.M]

Check the ON resistance of each relay while you have them out.  Power the coil for N.O. contact pairs and unpowered for N.C contact pairs.  If any are significantly higher than the rest, you *MAY* have a bad relay.

If your spec is correct they are open frame relays with accessible contacts.  If so, dragging a strip of cartridge paper wetted with a good brand of switch cleaner/lubricant through the closed contact pair may be all that's needed to clean them and resolve high contact resistance problems.

If the contacts are slightly burnt, try a strip of 400 grit or higher Wet&Dry paper folded so both sides have abrasive to dress the faces slightly. After using abrasive, clean twice with paper as previously described. 

If the contacts are badly burnt (visible pitting, distortion or heat related discolouration away from the contact faces), replace the relay.

[Armadillo]

If you can take close up photos of the board, both front and back in high resolution and send to us, as least we can troubleshoot and part trace the symptoms.

[james_s]

What exactly is the symptom? Relays are relatively easy to troubleshoot, but it would be helpful to know why you suspect the relay. Does anything happen when the thermostat calls for heat? Electric furnaces are fairly simple devices and troubleshooting is straightforward but it's helpful to take a methodical approach to narrow down the problem, don't just guess.

[smnmedic]

The problem first started a couple months ago when i had the ac unit on. I bought a fixer upper and when it started acting up I put it on the to do list, but now it's freezing and space heaters are not doing the job anymore.

I first noticed that the air handler was running and never shut off because it was starting to get cold outside and the temperature got down to the 60's inside. I switched it over to heat and if worked but opened the furnace up and found a shorted wire coming from one of the heating elements.

I made sure the wire was no longer live and let the heat run to warm the house back up. After it warmed up I turned everything off (even flipped beakers), assumed the wire just touched the case or another wire and shorted, and figured I'd run the heater on 2 elements until i had time to get a 10g wire to replace it with, but when I turned it back on and it wouldn't start. I checked to see if the thermostat was calling for heat and it was. I uncapped the wires that call for heat at the control board and there was power present.

I'm hoping the shorted wire was from what I said above and just a coincidence and because the air handler did not turn off and then not back on, that if was a relay?

I'm including a few pics of the board which I still have out and please forgive my soldering skills. The number 3 relay was not being used so I switched that out with number 2 (the relay powering the element that had the shorted wire) and I put relay 1 back in its place and will install it tomorrow and see if it works?

[smnmedic]

Here's are a few more. They were too big to include in last post

[smnmedic]

And the last 2 I took. Anything else you guys want me to do let me know?

[smnmedic]

The relays have optional dust covers installed and as you can see they are removable so I'll take your advice Ian.M and clean them before i put it back in.

[Armadillo]

hi, the back PCB is not clear enough, would it be possible to high res again.
Would prefer it to be like the first photo.

[Ian.M]

Do you have the furnace's wiring diagram?   If its not something simple like burnt or welded relay contacts, you'll probably need to set up a test jig so you can work your way through the circuit methodically on the bench with the relays hooked up to a low voltage supply and low voltage bulbs as loads so you can observe the results safely.   Everything except the TIV59288-1 custom chip is replaceable/rebuildable.

[smnmedic]

Sorry for taking so long to respond, but no i do not have a wiring diagram. I found replacement relays and installed them and is still not working correctly. The fan us running continuously. I disconnected the thermostat and it kept running. I d/c the low voltage wires at the furnace and the thermostat and it was still running. It only stopped when i d/c the common fan (purple wire to fan common) on the control board.

I'm assuming there's a short in the fan or on the board. I can't find the 185TIV59288-1, but have found a 185TIV59288-4. I'm wanting to replace the relay driver (uln2003a) and the 185TIV before spending $100 on a new fan.  Will the 185TIV59288-4 work in place of the 59288-1?

I tested for continuity on the pins of that chip and there was continuity between pins 10 and 12. No other pins on that chip had continuity. I'm thinking that's where the short is? I wouldn't think there would be continuity between those pins with no power/voltage applied?

[Ian.M]

You don't know if each disconnected sensor or control reads as active or inactive, and to answer that question, without a board schematic and a wiring diagram will need a fair bit of reverse engineering.

The 185TIV59288-4 may not be compatible - you'd need schematics of a board that used it for the same function and of your board to compare.  OTOH if its cheap enough, it may be worth the gamble.

[james_s]

The problem is not the fan, that's one thing I can tell you for sure. This is obvious because the fan is running.

The relay driver is a potential suspect, it's fairly easy to test. Look up the datasheet, then check the voltage on the input pin that controls the output wired to the relay. The ULN2003 is a very common integrated driver IC intended to drive relays and lamps and such.

I don't know what the 185TIV59288-1 is, it may be a custom microcontroller in which case you will not be able to substitute it. Experience suggests that exotic parts like that are not usually the problem.

[smnmedic]

I tested the pin voltages of ULN2003A and they were all right around 14.5v except pin #9 which was 13.65v. They were all 14.50 to 14.53 tested on AC voltage.

I also tested the bottom relay pins and they all matched. All the top relay pins were 119v. L1, T1, Fan = 119v, and L2, T2, Fan Common = 119v.

The voltage at the 3 heater posts were 119v as well as the 3 white common posts. I tested voltage at secondary transformer = 119v and where the 2 wires run end at the terminals that run to the capacitor and fan = 119v.

I'm lost at this point because I thought something would be wrong with the relay driver. I went back and even tested in DC voltage just in case i made a mistake and this is what they read:

1. -5.57v
2 through 6 -10.35v
7. -5.61v
8. -11.05v
9. 17.72v
10 through 12 -10.90v
13. -11.03v
14. -11.04v
15. -10.92v
16. -10.29v

The bottom pin relays all tested around -10.90 to -11.03 but one of the pins on the first relay was positive 10.32 (I'm pretty sure it was the second pin and the first was negative). I don't think any of this DC testing matters because there is no A to D converter on this PCB?

[james_s]

That doesn't make sense, the ULN2003 is a DC-only part, you shouldn't see AC voltage on it. What were you referencing the meter to? Does the fan relay engage when power is applied?

[smnmedic]

The top pin on the board of the secondary transformer hooks to the ground on the furnace so i put the black probe on that pin and the red probe to all the pins on the uln2003a. I thought that was a dc chip, but the power to the board is ac so are the capacitors on the board smoothing the ac waves into dc?

The two pins on the board that hook up to the secondary transformer has a red wire hooking to the bottom pin and a black wire that hooks to the top pin but also splits off with a green wire that goes to a ground screw on the case is the furnace. Since that pin hooks to a ground I assumed I could use that as my ground reference?

[james_s]

Some of those diodes on the board will be a rectifier that turns AC into DC, and one of those electrolytic capacitors will be a filter on the DC supply. You may have to draw up part of the schematic for that to be clear. The positive DC rail likely connects to one side of the relay coil and the other end of the coil will go to one of the pins on the ULN2003 IC.

[Ian.M]

ULN2003 pin 8 will be the 0V return to the filter cap - use it as the referece point for all votage measurements in the relay driver circuit.

[smnmedic]

Got ya, thanks! Will repost measurements later today.

[smnmedic]

Testing using pin 8 as ground reference:
1. 5.47v
2 thru 6. 0.690v
7. 5.45v
8.
9. 28.84v
10. 0.624v
11. 135.7mV
12. 28.0mV
13. 27.9mV
14. 135.6mV
15. 135.8mV
16. 0.744v

[smnmedic]

Any thoughts in regards to the pin voltages? The IC is just not gates with blocking diodes on the common so when it's high on pin 1 it should be low on pin 16 correct? The pins are linked straight across, 1 to 16...2 to 15...etc. with pin 8 as ground and 16 as common. The pins reading voltage in the mV range is just noise and is a logical low and the linked pin should be high, correct? 

If what I'm saying is correct this chip is faulty?

[smnmedic]

Sorry, I mean pin 9 as common.

[smnmedic]

Here the readings are easier to read with their counterparts.

1. 5.47v        16. 744mV
2. 690mV     15. 135.8mV
3. 691mV     14. 135.6mV
4. 691mV     13. 27.9mV
5. 690mV     12. 28.0mV
6. 692mV     11. 135.7mV
7. 5.47v        10. 624mV
8. Ground       9. 28.84v

[smnmedic]

So, this is the input and output of the IC if I'm reading this correct

1. High.        16. Low.    (Pass)
2. Low.         15. Low.    (Fail)
3. Low.         14. Low.    (Fail)
4. Low.         13. Low.    (Fail)
5. Low.         12. Low.    (Fail)
6. Low.         11. Low.    (Fail)
7. High.        10. Low.    (Pass)
8. Ground.      9. 28.84v (common)

Since they are all Not gates each Low input should result in a High output, but every Low input on this chip is resulting in a Low output and is faulty. I'm currently in college and I recently took a Digital Electronics course so I realize how basic this relay driver is and just want to make sure I'm not making some noob mistake like trying to use the case ground instead of the IC ground and doing something wrong!

Again, thanks for any help!