How do I test a furnace without a thermostat ?

[Jberger93]

I have a furnace that has no thermostat wires ran to it. Meaning, all the wires that were on the circuit board of the furnace are taken off. I wanted to test the blower motor so I ran a switch to it . When I turn it on , the blower motor spins about a half an inch . I'm assuming I have to wire the circuit board. How do I do this.

 

[larry4406]

"Red and White makes my furnace light".

Literally, connect the red and white terminals on the board and it will go into start up sequence and run full tilt for heat. Check the gas solenoid as many have an on/off switch and make sure it is on.

 

[dogdog]

dependents on what you got... usually R and W terminal, older ones might be T T.

 

[Bert_]

R is 24v power, W is call for heat, if it has a G terminal that is fan only.

R+W will be normal heating.

 

[Jberger93]

Thanks guys . It works!

 

[bubinga]

R is 24v power, W is call for heat, if it has a G terminal that is fan only.

R+W will be normal heating.

I'm going to piggyback on this thread.
I want to test my thermostat, jumping at the terminals on the back of the thermostat.
So, if R and W is call for heat, what would I jump
R to, to see if my A/C kicks on?
(This is an older style round thermostat,
No digital readout)

 

[Jim greengo]

I'm going to piggyback on this thread.
I want to test my thermostat, jumping at the terminals on the back of the thermostat.
So, if R and W is call for heat, what would I jump
R to, to see if my A/C kicks on?
(This is an older style round thermostat,
No digital readout)

Red and green and yellow or blue.

 

[bubinga]

Red and green and yellow or blue.

Thank you Jim
So I would jump all 3?
Red R 24 v and Green
Will power my fan, and jumpering in Yellow Y (Or blue) will start the sequence for the air conditioning correct?

 

[Jim greengo]

Thank you Jim
So I would jump all 3?
Red R 24 v and Green
Will power my fan, and jumpering in Yellow Y (Or blue) will start the sequence for the air conditioning correct?

Yes

 

[bubinga]

Yes

Thank You

 

[Jim greengo]

Thank You

Da nada

 

[bubinga]

Well I went downstairs to make sure the filter wasn't crazy clogged up or anything like that, maybe keeping it from kicking on, it was just a thought.
The filter is not too terribly dirty or anything.
Now I have not tried to jump the thermostat out yet.
However, when I went down to check the filter the blower motor was running (the fan switch is set to automatic)
Also the unit is running outside.
Could that still be a malfunction in the thermostat perhaps from the R terminal, to the yellow terminal of the thermostat?
I know it's definitely not cooling though I have the thermostat set to about 60° and the thermometer is reading 68 to 70°.
Thank you!

 

[Jim greengo]

Try removing thermostat and see if it shuts down.Depending on how new the furnace is ,it could also be a control board/relay problem.
Get that part figured out 1st,then throw a set of gauges on the outside unit to see what its doing.

 

[dogdog]

Well I went downstairs to make sure the filter wasn't crazy clogged up or anything like that, maybe keeping it from kicking on, it was just a thought.
The filter is not too terribly dirty or anything.
Now I have not tried to jump the thermostat out yet.
However, when I went down to check the filter the blower motor was running (the fan switch is set to automatic)
Also the unit is running outside.
Could that still be a malfunction in the thermostat perhaps from the R terminal, to the yellow terminal of the thermostat?
I know it's definitely not cooling though I have the thermostat set to about 60° and the thermometer is reading 68 to 70°.
Thank you!

if you are on heat setting, your thermostat is set at 60 and your temp is at 70, it should not run regardless of fan is on automatic or not.

but if you are on Cooling mode, your thermostat is set at 60, and your temp is at 70 it will try to cool the house down to 60.

check and make sure what mode your thermostat is set to. ? heating or cooling.

 

[bubinga]

if you are on heat setting, your thermostat is set at 60 and your temp is at 70, it should not run regardless of fan is on automatic or not.

but if you are on Cooling mode, your thermostat is set at 60, and your temp is at 70 it will try to cool the house down to 60.

check and make sure what mode your thermostat is set to. ? heating or cooling.

set to cooling

 

[bubinga]

Try removing thermostat and see if it shuts down. Depending on how new the furnace is ,it could also be a control board/relay problem.
Get that part figured out 1st,then throw a set of gauges on the outside unit to see what its doing.

Remove the thermostat and see if the blower shuts down you mean?
Can I just remove the wire to the R terminal, or do I have to remove all of the wires?
Thanks Guys!

Side note, It was running just fine the day before.
If I pull the control board, can one often see something burned up on the board. (If the board is bad)
I'm not sure how old the system is.
Would it pay me to set the thermostat to call for heat, go down and shut the power switch to off, turn it back on, and note the start up sequence?
I know the last one I worked on gave you codes.
Furnace isn't working either though, as I set it to the heat mode, and the room temperature is still around 60*

 

[bubinga]

OK, MY Bad!
The heat side of the system seems to still be working fine. I don't know, would it still be possible it is still a bad thermostat if the A//C is not working, but the heat is?

 

[dogdog]

OK, MY Bad!
The heat side of the system seems to still be working fine. I don't know, would it still be possible it is still a bad thermostat if the A//C is not working, but the heat is?

you were on cooling mode. by default if you set your temp to cooling and your set temp is at 60, your room temp is at 68, the system will turn on, and try to cool the house down to 60deg +/- 3 or what ever that error set at.

if your blower unit on the furnace is running, and the outside compressor fan is working. but your house or the air is not cool, it might be something else.

Normal system, usually only have 1 set of control wires to the outside unit and 24vac to control a contactor / relay for both the 240V condenser fan and compressor. so if that runs, it might not be electrical issue. well at least up to the contactor point (not control electronic issue)

 

[bubinga]

you were on cooling mode. by default if you set your temp to cooling and your set temp is at 60, your room temp is at 68, the system will turn on, and try to cool the house down to 60deg +/- 3 or what ever that error set at.

Yes, all of that I understand, and is working properly. And I am setting the Heat/Cooling mode properly, and setting the temperature dial correctly.

if your blower unit on the furnace is running, and the outside compressor fan is working. but your house or the air is not cool, it might be something else.

Normal system, usually only have 1 set of control wires to the outside unit and 24vac to control a contactor / relay for both the 240V condenser fan and compressor. so if that runs, it might not be electrical issue. well at least up to the contactor point (not control electronic issue)

So you are saying if the Blower motor on the furnace is running, and the outside compressor fan is running, I can eliminate the thermostat being the issue?

 

[dogdog]

"So you are saying if the Blower motor on the furnace is running, and the outside compressor fan is running, I can eliminate the thermostat being the issue?"

^^^
Yes. It would only be a problem if you are on cooling and your set target temp on thermostat is 68 and outside ambient temp reading is at 60 ( the reverse of what you got) and system turns on... that might be some issue...

There are only one set of control wires to the outdoor condenser / compressor unit... in most home AC systems, "most". if the contactor is engaged, the out door unit contactor is engaged... it's not thermostat issues I would say. all you have left is if the condenser fan running, verify if the compressor is running.. or at least voltage to the compressor... or monitoring the pressure. Usually there is an electrical diagram at the condenser unit panels. "Usually"

but voltage to the contactor and your furnace blower running, heater not engaged, that is normal in cooling mode.

Sorry , not expert enough to trouble shoot refrigerant pressure or calculate super heat those stuff yet. I need to pick that skill up to fix for my parent's place, same situation, blower runs, condenser fan runs, compressor runs (?), not cooling. suspect some bad installer since day one too cheap to purge when brazing the lines. (long story). dunno for sure, it's not been working since day one house was build..

There are few good youtubers doing subjects on super heat and recharging / condenser compressor diag.. one guy from florida Dr. Zyclop or something is great if he is still around... because he explains it, instead of show off with it like most youtuber. So you actually learn something instead of WOW he is amazing and learn learn nothing..

 

[dogdog]

LMFAO not DR. zyclop but DrZarkloff Interesting and very knowledge guy.

 

[bubinga]

LMFAO not DR. zyclop but DrZarkloff Interesting and very knowledge guy.

Thanks dog dog so my thermostat wires send the signal to the contactor on the board at the furnace and then the board sends the voltage signal to the outside unit correct?
Well I thought if it was the thermostat or maybe if I could trace it to being a bad board or something like that I could fix it myself I might have to get someone to look at it.
I don't have air conditioning gauges. thanks for all the explanation and everything.

 

[dogdog]

so my thermostat wires send the signal to the contactor on the board at the furnace and then the board sends the voltage signal to the outside unit correct?

Not sure if I can explain this but sort of yes
Your thermostat closes a contact (usually a smaller relay) between Rc(24Vac) and energized the Y wire that sends as a signal to the control board to turn on the cooling portion... then it energized a bigger relay that sends 24vac to energized the contactor (a bigger relay) at the condenser unit..

so sort of yes, a smaller relay energize a bigger relay to energized another bigger relay. with some logic board in between to also turn on fan (the blower) regardless if it is on manual of auto. If I remember correctly, if the G wire on the thermostat if set to manual it will always turn the blower on continuously. with the thermostat energized the G wire via another relay. If it is on auto, then the logic board takes control only to turn on blower before or after the heat is called... (not sure the exact logic, I guess it would be dependent on brand of the air handler control.)

For us mere mortals, If you call for cooling and conditions are right, your contactor energized at the condenser unit, I say the system is fine electronically.

Heat Pump Thermostat Wiring Diagram - Today's Homeowner

Installing or replacing a heat pump thermostat can improve your HVAC system’s efficiency and help you save on energy bills. Most modern thermostats cost

www.airconditioning-systems.com

 

[bubinga]

Well, I am actually am renting, but the mataince man is a PITA to get to fix anything.
If it was something simple like a thermostat,
I was just going to replace it, rather than listen to his B /S trying to blow smoke up my ***.
He has proven to me that he is a bull *******.
I know how he operates.
I expect him to come up here, and set the system to cool, put his hand over the air conditioning vent and tell me it's blowing cold air and it's okay.
If I was to get a thermometer on Amazon like this one I link to, how do I use it to prove to him that it's not working right.
I know I had this thing running for over an hour and a half and the temperature still stayed 10° over what I had it set to it never brought it down to where I had it set like it should.
But just in case he tries to blow smoke up my ***, how do I test this system with this thermometer if I have to prove it to him.
I get so anxious anytime anything goes wrong in this place because of the way he does.
I can actually fix a lot of things around here but I am not about to.
This is the one I was looking at.

https://www.amazon.com/dp/B004WE73N2/?tag=atomicindus08-20

 

[dogdog]

maybe this one. if you can splurge. Basically you need to proof ambient temp and the temp out of the vent at the same time. There is that thing about the AC can only cool so much. I don't remember, it's mentioned in one of those videos, or wait for a real HVAC guy here that knows calculations. I mean air flowing through the sensor will shows a few deg lower than ambient temp, but if the AC is working it should be at least 20deg lower,

basically give him two numbers so he can't feel it, its all in the measurement. Sorry don't know for sure how this will play out for you.

https://www.amazon.com/Thermometer-Thermocouples-50-1300°C-Temperature-Measurement/dp/B07P8NWH67/

 

[bubinga]

Ok, I texted him Saturday, never heard back So I called the landlord Monday, he said they'd check it.
Still haven't heard anything back.
I could have used it a few times too, but it's been cold for the most part.
Ok, I hope it don't start getting hot, and I won't have it.
Thanks Dog Dog

 

[Ohmthis]

Bubinga, we use delta T (that means the difference in Temperatures) between supply and return temps as a performance stat. Stick your thermometer into the return, note the temp. Stick it in the supply and note that temp. The difference (Delta T) should be 15-20*. If it’s less than that there is a problem. It could be that the dual run capacitor outside for the compressor is bad. This will let the fan outside run, but there will be no refrigerant pumping. Without refrigerant moving there will be no cool air. Hope this helps.

 

[bubinga]

Bubinga, we use delta T (that means the difference in Temperatures) between supply and return temps as a performance stat. Stick your thermometer into the return, note the temp. Stick it in the supply and note that temp. The difference (Delta T) should be 15-20*. If it’s less than that there is a problem. It could be that the dual run capacitor outside for the compressor is bad. This will let the fan outside run, but there will be no refrigerant pumping. Without refrigerant moving there will be no cool air. Hope this helps.

Yes, thank you.
Any easy way to check the cap myself?
They're still jagging me around with the A/C.
Then my electric entry lock quit working, l couldn't lock it from the outside, would just flash and beep 10 times.
I thought here we go,
Another run around to get this fixed.
Research it, 4 AA batteries were bad, that fixed it.

 

[Ohmthis]

Do you have an electrical meter? I can send you a link on how to test one.

 

[Ohmthis]

Here is a link to testing your capacitor. Be very careful, a capacitor holds a lot of electrical potential. Use this at your own risk.

Testing Capacitors

An HVACR capacitor can be tested after turning the power off, disconnecting the wiring, and bleeding off any leftover voltage before testing. This can be done with a multimeter on the uF or MFD setting. On a run capacitor, most of the voltage will drain off from the capacitor during the off...

www.acservicetech.com

 

[bubinga]

Well he finally got somebody up here it's been about a month or so ago maybe two months it was working good for a while
He said the AC guy said it was low but there was no leaks which I don't understand because as I understand that is not supposed to go low.
Anyways today it did not want to kick on.
I went down and took the top panel off and there's a bunch of condensation in the top it sounds like maybe my coil froze up. I don't know if that indicates low freon or if reduced airflow was the case I changed the air filter it did seem somewhat dirty.
How long would I have to wait for that to thaw out if it is frozen? If it was indeed the air filter causing it once that thaws out, it should start running okay correct?

 

[bubinga]

Well he finally got somebody up here it's been about a month or so ago maybe two months it was working good for a while
He said the AC guy said it was low but there was no leaks which I don't understand because as I understand that is not supposed to go low.
Anyways today it did not want to kick on.
I went down and took the top panel off and there's a bunch of condensation in the top it sounds like maybe my coil froze up. I don't know if that indicates low freon or if reduced airflow was the case I changed the air filter it did seem somewhat dirty.
How long would I have to wait for that to thaw out if it is frozen? If it was indeed the air filter causing it once that thaws out, it should start running okay correct?

All l know is i'm sweating my *** off, and God knows when or if he'll get someone here.
I talked to him yesterday, and he said, aw yeah, the girl net store's A/C isn't working either, I'll tell him to look at yours too.
I'm not holding my breath.
I notice with my A/C or heat off and fan set to run, the fan don't even run either.
Unless the fan motor went out.
I jumped R & G at the board and the fan didn't even come on. My HF light kept going off, l had to come up and charge it.
That thermostat and board should run off 24 volts DC correct?
I didn't appear to have any voltage between R(power) and C (common)
I unplugged the transformer going to the board and have 50& D/C volts there. I thought it was supposed to be only about 24 volts D/C?

 

[bubinga]

All l know is i'm sweating my *** off, and God knows when or if he'll get someone here.
I talked to him yesterday, and he said, aw yeah, the girl net store's A/C isn't working either, I'll tell him to look at yours too.
I'm not holding my breath.
I notice with my A/C or heat off and fan set to run, the fan don't even run either.
Unless the fan motor went out.
I jumped R & G at the board and the fan didn't even come on. My HF light kept going off, l had to come up and charge it.
That thermostat and board should run off 24 volts DC correct?
I didn't appear to have any voltage between R(power) and C (common)
I unplugged the transformer going to the board and have 50& D/C volts there. I thought it was supposed to be only about 24 volts D/C?

I was going to jump R and Yellow, Or Y, that should command the system to turn the A/C on, correct? But, again, my light kept shutting off. Also I understand, R (power) and G should command my fan on, correct, but it's not.
I did have a bunch of water in there, again, I'm pretty sure the A coil was froze up, but I couldn't get to it to look at it.
Can anyone offer any Ideas, I am roasting my *** off at around 80 degrees in here. And again, God knows when/If he'll get anybody up here. All he ever does is try to blow smoke up my ***.
The fan (at least so far) is running outside when l turn the A/C on. Not sure if the compressor is kicking on though.
Big hassle to get anything fixed around here.

 

[James Diaz]

I have a furnace that has no thermostat wires ran to it. Meaning, all the wires that were on the circuit board of the furnace are taken off. I wanted to test the blower motor so I ran a switch to it . When I turn it on , the blower motor spins about a half an inch . I'm assuming I have to wire the circuit board. How do I do this.

How to test a furnace without a thermostat?​

If your furnace doesn't have a thermostat, you can still test it to see if it's working correctly. To do this, you'll need to:

1. Check the furnace's power supply. Make sure that the furnace is plugged in and that the circuit breaker hasn't tripped.

2. Inspect the furnace's filters. If they're dirty, replace them with clean ones.

3. Test the furnace's igniter. If it's not working, the furnace won't be able to start.

4. Check the furnace's flame sensor. This component ensures that the furnace's flame is always burning. If it's not working, the furnace won't be able to operate safely.

5. Inspect the furnace's blower. This component ensures that air is circulated through the furnace. If it's not working, the furnace won't be able to heat your home correctly.

 

[bubinga]

I am trying to work on the AC part of it not the furnace right now. As stated I don't even have any fan with the unit off and set to on the fan set you on. I can't even get the blower to run. I did jump out R power which is power. To G witch should be the fan and it does not kick on.
When checking for voltage at the board shouldn't that red wire and common have 24 volts all the time? Although I believe I had my voltmeter set on DC because I thought it was DC. But I thought it should still read something. A follow on YouTube was showing a 3 amp fuse in the board but for the life of me I don't see a fuse in there anywhere. Again I am burning up in this place It's almost 80° in here.

 

[jd_1138]

Good luck, HVAC is one area I leave to the pro's. It's either me wasting 4 hours and frustration or calling them and having a $150 bill or so (but at least the HVAC is working).

I can do simple repairs, but if it starts eating into my R and R time, I call the HVAC guy.

 

[bubinga]

Good luck, HVAC is one area I leave to the pro's. It's either me wasting 4 hours and frustration or calling them and having a $150 bill or so (but at least the HVAC is working).

I can do simple repairs, but if it starts eating into my R and R time, I call the HVAC guy.

I hear you loud and clear on all that buddy but the thing of it is you don't know what a p i t a this so-called maintenance guy is here it is so hard to get them to do anything he tries to blow smoke up your *** I'm burning up in this place I'm just trying to get me some air I am burning up it's almost 80 in here. There's three units in here he told me that girl next door hers is out also.
She's been here a month, and I'll bet it hasn't been working since she moved in either.
Like I said does anyone know if all of those control boards have a fuse on them because again for the life of me I cannot see a fuse anywhere.

 

[bubinga]

I am just trying to avoid a month of frustration arguing with this darn guy.
And furthermore he thinks he's talking to a dummy he tried to tell me that the AC service guy could not keep Freon very long, I said, why what happens to it? "well it goes bad I guess" LOL he said you don't know about this freon on these home air conditioners I told him I know a lot ******** more than you think!

 

[bubinga]

Good luck, HVAC is one area I leave to the pro's. It's either me wasting 4 hours and frustration or calling them and having a $150 bill or so (but at least the HVAC is working).

I can do simple repairs, but if it starts eating into my R and R time, I call the HVAC guy.

l understand. Also I've already fixed about 4 different furnaces.
Some jagoff already "fixed" this A/C about 2 months or 1 month ago.