HVAC stopped, Transformer?

[Guest]

 I'm attempting to fix my son's A/C, which is a heatpump and I'm having some trouble. I'm glad I found your site. The air handler is a Radco? about 10 years old, and the compressor is older. They came home and turned on the heat and it ran for about 20 minutes and later they noticed it was off and getting cold. Nothing worked, turned the fan to on, still nothing, turned the humidistat to on, still nothing.

I went over, checked the breakers to the air handler and to the compressor, OK. I checked both were getting power after the breakers at the units OK. Then I checked if old Honeywell mercury thermostat had 24v at the terminals, no. Then I checked the circuit board a HK61Ga001a, and the 5amp fuse was OK.

By the way capacitor on the blower motor looked OK, no leakage, not swollen. The transformer looked old or covered in a brown glaze which could be a protective cover.

I'm guessing it might be the transformer and told my son my that. He ordered a new one, of course it had different wires. Old one was a HT01CN230a , had 5 wires, Black,blue,red that I think are com,208v,230v. and a red and brown on the other side that I think are 24v. The new transformer a 4031fk Gemtech has 6 wires I put Old Black to new black, old blue to new red 208, old red to new orange240, capped off white 120v, then Old 24v brown to new blue, and old 24v red to new 24v yellow.I turned power back on, no voltage at thermostat, none at, terminals in air handler to thermostat, none coming out of the transformer. Yes I show power to the transformer. I'm using a Tenma 72-4030 digital meter. What am I doing wrong? A new transformer couldn't be bad, so I must have screwed it up? I made all connections with the power off. I looked for an obvious short at the thermostat like wires touching at terminals and at the circuit board and didn't see any. I guess I should disconnect all terminals and look for crossed wires but the thermostat is on wall next to the unit and the wire jacket looks good. They had trouble before and couldn't get it to turn on and it was the humidistat set wrong, they turned it to on. He wanted it gone. I disconnected it and wired the red wire from the thermostat directly to the terminal of the circuit board instead of through the humidistat, to the circuit board. So what did I do wrong, or what should I try next?

[hvacdrd]

[user=20917]digitalchrisg[/user] wrote:

Black,blue,red that I think are com,208v,230v. and a red and brown on the other side that I think are 24v. The new transformer a 4031fk Gemtech has 6 wires I put Old Black to new black, old blue to new red 208, old red to new orange240, capped off white 120v, then Old 24v brown to new blue, and old 24v red to new 24v yellow.

Any multi-tap transformer I have seen you only use 4 of the 6 wires. The transformer should be labled something like this. 240V - Black & Red, 208V - Black & Orange, 120V Black & White...meaning you only use two of the 4 wires on the primary(input voltage) side of the transformer. The Yellow and Blue are the 24V secondary regardless of input.

If input is 240V White & Orange are capped off separately...

[dkpd1581]

Go back out to the t-former....according to you put black to black, blue to red and red to orange.  You have the 208 AND the 230 taps wired at the same time.  Thats a no can do.  Look and verify the high voltage value feeding the airhandler (prob 230 for residential).  Look on the body of the new t-former and the sticker will tell you which of the leads is the common and which is the 230 vac lead...tape off all of the rest and only use those two.

You may have damaged you t-former hooking it up like you have.  Verify continuity through the windings on both the high and low side before putting it back in.  Goto the t-stat and since it is mercury bulb, take the cover off and look for a hair thin wire behind the curled up bi-metal.  It is called a heat anticipator and verify that it is not burned which will keep you from getting 24 vac to the air handler

Let me know whatcha find and we can go from there

[Guest]

I know I had the 208 and 230 wired at the same time but that was how the original transformer was wired to the circuit board. I assume the circuit board selected which to power. I tried disconnecting each, one at a time but no good. I just can't get any juice. I also looked for the heat anticipator and could not see anything. Maybe I should try the 120 white? I don't know and its driving me nuts.

Here is a diagram of the transformers and a close up of the new transformers face plate. Any ideas would be appreciated.

Thanks for the help.

[dkpd1581]

Oki...seems like you have a good grip on how to use a meter so lets make this simple - HVAC aint rocket science:

1.  check the voltage going to the air handler where main power lines come inside the box.

2.  record this voltage because this is what we are going to use to set our transformer later.

3. power off to the air handler and then check for and ohm reading indicating continuity between the common lead and the proper voltage lead on the HIGH side of the t-former.  No continuity means no 24 vac can be induced in the other side - replace the t-former.

4. if there is continuity on the HIGH side ... then check for continuity on the LOW 24 vac side (no continuity then replace t-former).

5. if there is continuity on the HIGH and the LOW, connect the HIGH side common and proper voltage lead (120, 208 or 230) to the incoming HIGH voltage terminal block and make sure all other leads are tapped of.  Seperate the two LOW voltage leads so they do not touch anything, turn the power back on, and then check for voltage between the two LOW voltage leads - expect 24-28 vac.

6. if 24-28 vac is present, turn off power, connect the low voltage leads to their respective terminals. If none, verify connections and re-test.  Still no voltage, replace t-former.

7. power off, remove the low voltage fuse from the board and check for continuity. If none then replace.

8. install fuse, return power, check for 24-28 vac into the board (where the fuse you just replaced is - check on each side of where it snaps in). No 24-28 vac replace fuse. If still no 24-28 vac replace board.

9. check for 24-28 vac at the R terminal coming out of the board where the t-stat wire begins and goes out to the t-stat (you may see other markings such as Y, G, W,C). If none - replace board.

10. if 24-28 vac going out of the board, check to see if it is at the t-stat sub-base. If no voltage at sub-base, replace t-stat wire.

11. if 24-28 vac to sub base of t-stat move selector to fan on, cool on, heat on. If no response on any of these modes - replace t-stat.

This should get you along the road to an answer. Lemme know how it goes.

[Guest]

Thanks everyone for your replies, its fixed. As I was reading [user=16896]dkpd1581[/user]'s  great step by step advice, I remembered when I was testing the legs I did not open the circuit or test across the legs for 230v. I felt it couldn't be the power and just tested each leg to ground and got 115v with the circuit closed and went on. It hit me this morning as I was reading [user=16896]dkpd1581[/user]'s advice and I ran over to my sons house to find one leg was out. Then I had to find a double pull 50amp Zinco p.o.s. Man I'm stupid, could have fixed this way back in the beginning. Thanks again everyone!