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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22679
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Billy. It's Chicago again. Charge went well last night but

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Hey Billy. It's Chicago Dave again. Charge went well last night but now I need help on my secondary a/c I use for my garage only. It is a Bryant Model 590ANX036000ABA. I knew I had a problem when I called for cooling and the condensor did not kick on. I heard the thermostat click but I have no voltage across my thermostat wires at the condensor. I can manually start the condensor by pushing the little button on the contactor but it will not hold in because I'm not getting a signal to the contactor. I'm pretty sure it's not the thermostat but if it's not that I'm not sure where to look unless a part of the board is bad. What do you think?
That should be 24VAC to the contactor correct?

Hi Dave,

what do you have a blower inside?

Does it drain to a pump?

Customer: replied 5 months ago.
Ooooops. Should have told you I have a furnace as well. I just drain into a 5 gal bucket. Do you need model number of furnace?

at furnace....thermostat terminal C to Y (with ac calling) do you have 24v at that point?

Customer: replied 5 months ago.
I'm gonna run right out there and test that baby.

just let me know

Customer: replied 5 months ago.
DEADER than a door nail. Any way to bypass and still have the blower motor engage or do i have to get a new board?


at the board (and remember to tape the door safety switch down)...if you use a jumper R to G (on board) does the blower start insisde?

Customer: replied 5 months ago.
I tried the heat cycle. No dice. I think the board is fried. I'll quick go use my jumpers and see what happens
but i"m pretty sure I already know the answer. Be right back. This is good trouble shooting for me. I remember doing this
in the past but it has been a long time.

be a good time to see if 24v C to R on the board to make sure we even have 24v available

Customer: replied 5 months ago.
No blower R to G
No 24v C to R
Customer: replied 5 months ago.
I did remember to hold door safety switch down

the black and white supply wires 120v...goes to door switch and then board, do you have 120v on those 2

Customer: replied 5 months ago.
I know I have 120v to the switch. Didn't think about other side. Be right back.

or get me model number or pic of the board and I can circle test points

Customer: replied 5 months ago.
I have 120v coming out of the safety switch
I have 120v to transformer
I have 24vac out of transformerC to Y No 24vac
C to R No 24vacR to G with safety switch engaged No blower motorNot looking too well for that board does it?

you sure the limit or roll out is not tripped?

did you get model number or pic?

Customer: replied 5 months ago.
OK. Ya got me there. Not sure where the limit or roll out is located. I'm sorry but I
just saw your request for a pic or model number. I assume you want model number of furnace.Tempstar Model#NUG5075BFB1

on the circuit board....does the 24v wires attach to terminals labeled xfmr and sec?

Customer: replied 5 months ago.
I'll go check but wanted you to know the furnace worked perfectly all winter so this is a little confusing.

no 24v fuse on board or inline?

You may be right about the board..just wanted to confirm

Customer: replied 5 months ago.
OK. Things are getting plain weird. I just put the furnace in heat mode and I had a perfect start up and shut down.
I did check on the circuit board and did not see either one.
I just set thermostat to cool and the blower motor kicked on as I would expect. However the condensor has not
turned on yet. It may have a delay but I wouldn't think it would be this long. I will go check outside for 24v
Customer: replied 5 months ago.
No 24v fuse. I do know to check for that. It was one of the first things I looked for.
Customer: replied 5 months ago.
No 24v outside. I'm just not getting 24v out there. Do you know why the blower motor engaged
when I set the thermostat to cool and does that mean the thermostat is operating normally with
the switch in the cool mode? Can I bypass circuit board to engage condensor? By the way, thanks
for sticking with me.
Customer: replied 5 months ago.
Well I know why the blower motor engaged. That's what it's supposed to do. Sorry about that question.

ok just in case....last test....

at circuit board...jump R to Y.....I assume you have 2 wires in Y on circuit board ....and if not they are wire nutted together.

Bacically we want R terminal shorted to the Y wires...tell me if condenser starts

Customer: replied 5 months ago.
I do have 2 wires on the Y. I will go jump R to Y. Be right back.
Customer: replied 5 months ago.
I jumped R to Y. Blower motor engaged but not condensor. I held safety switch for at least 2 minutes
in case the condensor had a long delay built in. Maybe 2 minutes is not long enough so I left the jumper
in place and put the lower panel back on. Will let it run for 5 minutes and get back to you.

ok so we know we sent 24v to condenser...and if it did not pull contactor in...

wire connection


high or low pressure switch

If it DID pull in contactor but no start = 220v thing like supply, capacitor etc..

Jumping r to y bypassed tstat so I would make sure 24v comes from stat on y.....some stats with delays get a stuck delay and y never energizes

Customer: replied 5 months ago.
OK. Here is where I stand. I was NEVER able to get 24v out to condensor. I checked line from furnace to condensor to
see if there was an obvious break in the wire. I saw none but can check continuity tomorrow. What I am still trying to
understand is by jumping r to y to bypass stat, wouldn't that take the stat out of the equation. I thought jumping r to y
would send 24v to condensor but I don't know that for sure. If I don't get 24v to contactor it will never energize unit no matter what. Not sure what capacitor has to do with this issue as it's function is to help compressor start once contactor pulls in. Did a visual check on capacitor earlier and didn't see the obvious signs of bulging. I know they can go bad without that happening but again if I don't get 24v to contactor the capacitor is just going to sit there. In one of my earlier tests I did indeed jump
r to y but did not get 24v to contactor. In all the tests today the contactor never pulled in on its own. I had to manually push
in the button on the contactor to get the condensor to energize but it stayed on as long as I held that button down. That should rule out bad capacitor. So I guess bot***** *****ne is still the same issue. Why can't I get 24v to the contactor. Once I figure that out I know the unit will run.

jumping r to y sends 24v direct....the only things in the way are any bad connections, refrigerant low pressure, high pressure or delay boards.

The next step is to see if there is 24v on the 2 wire BEFORE it enters the condenser. Once it enters the condenser then it could be held up by a pressure switch.

If you press the contactor in does the compressor and fan start

Customer: replied 5 months ago.
When I press the contactor in manually the fan and compressor engage beautifully.
I measured that 2 wire several times today under various conditions as we were testing. Never once measured 24v.
Since jumping r to y should have sent 24v to contactor I would have measured 24v at the place you are speaking about.
One last time. Where should I be able to measure 24v at the board? Between what screws on the board with the stat in the cooling position. And if under those conditions I do not measure 24v would that not point to a bad board. What about low freon. Would that prevent 24v from being fed to the 2 wire going outside? If so I could put my gauges on in the morning
and manually start the condensor to see what my pressures are.

Give me a bit and I am going to draw up something

Customer: replied 5 months ago.
One more thing regarding the manual start up today. The fan kicked on immediately but to be perfectly honest with
you I can't tell you whether or not the compressor kicked in.
Customer: replied 5 months ago.
Thanks Billy. Sorry I've turned into such a pain in the ass. I really thought I could figure this out. I've done my fair
share of service but obviously I haven't seen any where near what you have seen. I'm just frustrated because I know
the basic circuitry but this one has me stumped.

use this rough sketch to mark where you read 24v and where you dont..the yellow wires are our main concern

Customer: replied 5 months ago.
On your drawing it appears the high and low pressure switches are in the condensing unit. How would I measure that
to see if it is the problem? I guess my main questin is does that yellow wire actually pass through those pressure
switches before hitting one side of the contacor. From everything I saw today the two wire simply came to the contactor
and each wire went to either side of the contactor. I didn't see any wire going thru switches of any type before connecting to the contactor. From your drawing I was never able to measure 24v across r and y. I'm pretty sure I get your drawing other than the yellow line going thru the pressure switches. The board is being energized by the transformer which we know to be good. So by jumping r to y we should have sent 24v to contactor. However, when I tested r to y at the board I never measured 24v. When I jumped r to y at the board bypassing stat I never measured 24v at the contactor. Again, for some reason I cannot get 24v outside. I know it's getting late. Don't want to keep you up. It's only my garage. You are sending me back to school
and believe it or not I'm enjoying your directions.

if the 2 wire actually goes STRAIGHT to the contactor, then you do not have any safetys, which is odd but possible.

lets eliminate the thermostat as suspect....take the red (r), yellow (y) and green (g) and twist them directly together.

then test for 24v

Customer: replied 5 months ago.
Sorry Billy. I just reset the computer and I just saw your last response. Just so I understand.
You want me to disconnect the r,y, and g at the thermostat and twist together.
Should I test for 24v at the condensor with the safety switch depressed?

tape door safety switch down

remove thermostat top section

take r (24v) Y (compressor) and G (fan) and twist together

tell me if 24v at the points HERE

Customer: replied 5 months ago.
I twisted the 3 wires together.
The blower motor on the furnace engaged.
No 24v at the two wire as it comes out of the house.
And the 2 wire definitely goes directly to the contactor.
Customer: replied 5 months ago.
I also tested at the contactor points as well. No 24v
We're just not getting 24v outside.Furnace still works in heat mode.
Ok we are making the y wire from board towards the outdoor unit. Does it go to anything else before it goes outside.....follow that wire all the way to condenser looking for breaks or a water safety switch....we are in the homestretch
Customer: replied 5 months ago.
I checked that yesterday. I followed from board directly to outside unit. I did not see any obvious breaks. I installed this unit about 4 years ago so I'm pretty familiar with the install. The 2 wire goes directly to the contactor. What I am going to do next is make the 2 wire a loop and see if I get continuity. That will confirm whether or not there is a break inside the sheathing. Will get back to you.
Customer: replied 5 months ago.
I have continuity so no break in the line. I know I don't have enough service background but it just seems to me the portion of the board responsible for sending 24v outside is not functioning. I know the transformer is putting out the 24v but I have never been able to measure 24v at the board.
Customer: replied 5 months ago.
When I say at the board I mean across the terminals you instructed me to test.

the board actually does not send 24v to unit outside. Y terminal is a dummy that is there just to mount wires...if you removed the 2 wires from Y and wire nutted them together it would do the same purpose.

Now follow Y wire from board back towards thermostat....if you have an extra wire not used in the thermostat cable swap it both ends...

Customer: replied 5 months ago.
Just wanted to let you know I was gone most of the evening. I only have 4 wires in the bundle. Am I doing this to check for breaks in that line. Do you think thermostat could be bad on the cooling side. I have several thermostats here at the house. Should I just try a new one. I'll check the current stat wires to make sure there are no breaks but if not would the next step be to try new stat?
Customer: replied 5 months ago.
I lied. I do have extra wires in the bundle. Will try different wire in the morning. However, I did do a stat switch and still have the same problem. The furnace does a perfect heat cycle but when I call for cooling the blower motor engages but not the condensing unit. The story continues. I hope you have a good night. Dave
Customer: replied 5 months ago.
One last thing. The thermostat simply acts as a switch. When the stat calls for cooling the switch opens and allows the 24v to flow back to the board and presumably out to the contactor. What is energizing the wire going TO the thermostat. Like any other switch shouldn't that line have a constant feed of 24v just waiting for the stat to open? Is the transformer supposed to be feeding the terminal board with a constant 24v and if shouldn't we be able to measure the 24v at the terminal strip which is what I thought we did in one of the earlier diagnostics. Just trying to think logically thru the process.

The 24v starts from R terminal on board

Goes to R terminal on thermostat

The thermostat acts as a traffic cop...sending back on whatever wire for a given function.

In this case it sends back on green for fan...and Y for cooling.

We know it is sending back on G as the blower starts

We know we have bypassed the thermostat by twisting r,g,y, together which eliminates stat as suspect.

Our only loose end is Y signal between thermostat and circuit board.

Now to narrow down further..

furnace door switch taped down.

Thermostat r,g,y, twisted together

with meter at furnace....measure c to r......c to g.....c to y.

Tell me those readings and we have a final area to deal with

Customer: replied 5 months ago.
I'm back.c to r = 24v
c to g = 24v
c to y = no 24v

them y wire is open between thermostat and furnace.

at furnace..take the y wire from the outdoor unit...and touch it to R with the door switch taped down

Customer: replied 5 months ago.
Should I leave the 3 wires that are currently twisted together connected or should I untwist them and then do the test?

for right now just do the jump from circuit board R to Y

Like here

Customer: replied 5 months ago.
I'm going to run the test now but just to let you know I checked for continuity on the y wire between stat and circuit board. There is no break in that line. Will get back to you when I have jumped r to y
Customer: replied 5 months ago.
OK. Here is the latest.
with the r g w twisted together
c to g = 24v
c to y NO 24v
c to w = 24v
c to r = 24v
r to y = 24v
I jumped r to y as instructed but realized I didn't know what I was supposed to be looking for as a result of the jump.
The condensor did not turn on as a result so if I need to look for something else you will have to tell me.

ok lets be straight have r,g an y twisted...not rgw?

Customer: replied 5 months ago.
I don't remember what I did the first time you told me to twist the 3 wires together because I changed out the thermostat to see if that would help. When it didn't it appears I screwed up and twisted the wrong 3 together. Maybe I had the wrong 3 twisted from day one. If so I'm an idiot and apologize. Long story short I twisted R G Y and did the following tests.c to r NO 24v
c to g NO 24v
c to Y NO 24v
Customer: replied 5 months ago.
But the blower motor is on

check to see if we blew a fuse....

c-r = zero is blown fuse or no power

Customer: replied 5 months ago.
on my way
Customer: replied 5 months ago.
I can find no fuse. I know most furnaces have them to protect the electronics but I don't see one.
c to w has 24v
One other thing. My neighbor just told me they have been hearing "clicking" noises from the condensor for the
past few minutes. Something must be getting out there.
The furnace transformer is still putting out 24v

undo all thermostat wires.

Before we continue, does the unit start if you press contactor in?

Customer: replied 5 months ago.
Still nothing c to r c to g c to y
Customer: replied 5 months ago.
just to be sure. You want r g y twisted?
When I had r g w twisted I had 24v to everything except c to y

for now we are even eliminating that....we will do everything just at the circuit board in furnace with door switch taped down.

you can even put thermostat back together. All I need now before we do the next step is to know if the outdoor unit starts when contactor pressed in

Customer: replied 5 months ago.
the outdoor unit starts. I'm going to untwist all the wires so the r g w and y will just be hanging free. I will deal with
the stat hook up later.
Customer: replied 5 months ago.
wires apart. blower motor stopped. door switch still taped on

ok so unit starts when contactor pressed. so we have 220v ok.

we have 24v inside which means we have 120v plus working transformer.

Now with jumpers....

put jumper on r and g confirm blower starts

Customer: replied 5 months ago.
started right up


Now remove jumper and put r to w - confirm heat starts and remove jumper.

Then install jumper R to Y - if condenser does NOT start see if 24v at at unit where wire first attaches

Customer: replied 5 months ago.
On my way
Customer: replied 5 months ago.
r to w heat startsr to y blower motor engages as I would expect but no 24v at 2 wire going into condensor
Just for grins I measured across r and y terminal no 24v don't know if there is supposed to be but if you are supposed to have 24v there is none

can you take a pic of the circuit board in the furnace and post here please?

Customer: replied 5 months ago.
Hope this is it
Customer: replied 5 months ago.
I sent one I think. Let me know. I've never done it before

great job....

I see we have two the black wire the one that runs outside? and the red on c runs outside?

So black and red run to outdoor unit?

Customer: replied 5 months ago.
That is correct. Black and red run outside and that hasn't changed since the day I installed unit.


move the black wire off Y....and mount in the R terminal.

Then see if 24v outside.

Customer: replied 5 months ago.
Moved black wire to off y and connected to R terminal. NO 24v There must be a break in that 2 wire yet I had continuity through both the black and red wire so I'm just out of ideas.
Customer: replied 5 months ago.
I am simply not getting 24v outside. I assume you were taking a known 24v source and just testing to see if it would go outside.

Ok, very simply...we put the 2 wire (black and red) direct to 24v+ and 24-

and you say the 2 wire goes straight to the contactor.

Since we are sending from a confirmed has to be stopped somewhere before the outdoor unit.

This has taken the thermostat out of pic....thermostat wire between furn and stat...

This narrows down to a direct 24v+ to the outdoor 2 wire.....there is a switch, break, cut, etc somewhere on that red and black wire between the ac unit and the furnace.

Customer: replied 5 months ago.
Well in most cases I would agree with you but I just measured C to R NO 24v
So I measured C to W C to G C to Y All these measured 24v

put meter black to metal ground

put meter red to R.

Customer: replied 5 months ago.
Black to metal ground = 24v
I don't understand where to place probes on red to R

ok, what I meant was black meter lead to metal cabinet

red meter lead to terminal R on circuit board

Customer: replied 5 months ago.
I measured 24v
I think I'm going to run a new 2 wire from the furnace and see what happens.
Since I have 24v at the R terminal it should have gone outside, right?


r to ground = 24v

r to c should also = 24v

Unless the board has lost the common side circuitry

Customer: replied 5 months ago.
Here's the problem.R to metal ground = 24v
R to C NO 24VI don't know what that means in the service world but in my world it means the condensor will not function

actually that means nothing requiring a commom would work including heat. Common is the end point for everything.

Just for giggles..move the red wire from C to metal connection...many times the transformer has a wire to ground.

Move the red c wire to metal cabinet and attach...then jump r to y....measure 24 at condenser..remember R to C that = nothing could be board.....

Customer: replied 5 months ago.
Will do. Just for added info I toned both my 2 wires. There is no break in that 2 wire.

move the C red wire to furnace metal connection...pretend furnace metal is common

Customer: replied 5 months ago.
Is the red wire you're referring to the 2 wire or the one off the terminal?

you have a red from outdoor ac on C

and a black wire on Y from outdoor ac.

remove the red wire from outdoor ac unit on c and connect to metal ground.

Customer: replied 5 months ago.
You had me move black wire from outside to red furnace terminal.
I will put black wire back to yellow terminal and remove the red wire from outside currently connected to C on terminal strip and connect to ground
Customer: replied 5 months ago.
What am I looking for

correct....either will suffice.

we have 24v.....but we ar not reading 24 common through board.

You said terminal R to Terminal C = 0

But terminal R to metal ground = 24v

Thus we are missing common.....common to terminal R should read the same as terminal R to ground

Customer: replied 5 months ago.
let me see if I understand.Since we do not have 24v from C to R and that has been the case throughout this nightmare there is no way
we are going to send 24v to the condensor which requires R and Y to function properly. Are you saying it is
possible to lose just that one piece of the board because that is exactly what appears to be happening.
Customer: replied 5 months ago.
if I want a/c this summer I will need a new board or just live without it. The furnace function is way more
important to me. The winters are cold here and it's nice to keep the cars warm.


This is the same as having an open neutral in an electrical panel.

You have 120v to ground..but the neutral is bad.

For example.....if you attached your 2 wire from outside direct to the transformer (24v side) the contactor may oprerate.

There is such a thing as a 24v transformer with an open common. I know you have been through heck here....but is there a way you can test the transformer output wires? Wire to wire?

Customer: replied 5 months ago.
If you can explain how to do it I will give it a try. By the way, I think it is you who has been through alot. You don't know how much I appeciate you sticking with me. I would have given you 5 stars a long time ago whether or not we figured this out.Theoretically, since I can engage the blower motor I could take a 24vac transformer, put a switch in line and operate the condensor manually. I would just have to switch on and off as necessary. The blower motor could run continuously untiI I was done with whatever project I was working on in the garage. I have all kinds of spare transformers.

yes...the circuit board is strictly heat and fan related.

That is why I asked you to move the red wire from ac unit to see if we can close the contactor on ground instead of common.

Also as far as temp use....I have even seen the contactor bypassed with the 220v direct to output side of contactor....

It runs all the time until disconnect pulled or breaker thrown...but in a pinch this turn on fan....and then turn on lose thermostat control but have ac when you need it.

BillyHvac and other HVAC Specialists are ready to help you
Customer: replied 5 months ago.
I never did get around to moving red wire from a/c to ground. I will do that tomorrow just to see what happens. Good
practice for me. I believe we are both in agreement that a new board is in order. This unit has worked perfectly for 5 years
and for it to suddenly stop working usually points to a component failure of some kind especially if the rest of the functions are working. Go to bed. It's getting late and my old bones can't take much more. Had a garage sale this weekend. Never again. The sale part is not so bad but getting ready for it is horrendous. I am exhausted. Have a nice evening. Sorry I took up so much of your time. I made alot of notes so if I ever run into something like this (and I probably won't) I will know what to do.
Regards, Dave
Customer: replied 5 months ago.
Hi Billy. Thought you might like an update. I got the a/c to work today. Did not put in a new board. Not worth the expense.I simply wired a 24vac transformer with a switch in line to the 2 wire going out to the condensor.
When I want cooling I simply energize the blower motor and flip the in line switch .
Condensor fires up and I have cooling!