Short #85 - Low Voltage, Low Voltage
HVAC School - For Techs, By Techs
Bryan Orr
4.9 • 1K Ratings
🗓️ 7 January 2020
⏱️ 13 minutes
🧾️ Download transcript
Summary
In this short podcast episode, Bryan explains what happens when your low-voltage circuit puts out a lower voltage than it should.
Bryan recently received an email asking about the low voltage on a 20-ton split system with a long control wire; the voltage coming back to the condenser is only 19 volts, so there was some contactor chattering. First, in a case like that, you'll want to figure out why the voltage isn't as high as it should be. The control wire and line sets could be longer than the design specs, which may contribute to the problem. If the distance between components is the main issue, then you can use a relay to mitigate voltage drop and amp draw.
You'll also want to check that you've tapped the transformer correctly. Since most transformers are single-phase, they'll probably start off tapped to 240v; when you're dealing with three-phase equipment, you must ensure that the transformer is tapped to 208v.
One of the obvious issues to check is the voltage drop. If 26 volts are coming out of the transformer but you're only measuring 19, then you're clearly losing volts and have some resistance. Think about ALL of the conductors; is the drop the same across all of them? If so, then you've likely got a length and wire sizing problem. You can correct that issue with proper wire sizing; you can't always control the length, but if you can, then it's a good issue to address. If there's an issue with only one conductor, then the switch could have a problem, or there might be some wire splices.
If the load is drawing higher current than it should, then something could be impeding the motion on the solenoid, contactor, or another electrical component.
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Transcript
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| 0:00.0 | All right, so this is the HVAC school podcast. This is a short episode, and this is a ride-along episode I am driving, but my eyes are on the road. Fear not. Fear not. This short |
| 0:16.1 | episode is going to be about low voltage, low voltage, based on an email |
| 0:20.4 | question that I got. Thank you for those of you who send in questions. I do confess |
| 0:24.8 | that nowadays I get a lot of questions that are manufacturer specific questions and I generally |
| 0:29.8 | don't even answer those because the reality is is that unless you're talking about |
| 0:34.3 | carrier equipment from 10 years ago I'm probably not the best person to ask |
| 0:38.7 | manufacturer specific questions truthfully I'm just gonna read the manual so that's what I would suggest that you do if you haven't already or go into one of the groups and share there which by the way if you're not part of the |
| 0:49.1 | HVAC school Facebook group that's a good place to go and ask questions it's generally a pretty |
| 0:53.0 | helpful place sometimes there's some snark but if you're anything like me |
| 0:57.4 | sarcasm is my love language so first I want to thank our sponsors for a sponsor to thank is carrier and carrier. |
| 1:04.5 | carrier.com carrier has been a long time partner with us and like any long-term business |
| 1:10.0 | relationship I think it's important to note that there are ups and downs. |
| 1:13.4 | There are things that ebb and flow, things that are problems that need fixing and what I've liked |
| 1:18.7 | about working with Carrier and specifically Carrier Enterprise Florida is that they have always worked with me. |
| 1:23.3 | They've always respected the relationship and worked hard to make things better, and that's all that you can hope for. |
| 1:29.4 | So if you want to find out more about becoming a carrier dealer, go to carrier.com. Also I want to thank |
| 1:34.3 | speed clean. Speed clean has been a really great partner in training. They are |
| 1:38.5 | one of those companies that is excited about education for education sake, which to me makes a huge difference in a |
| 1:45.4 | partnership like this because there are some cases people just want you to advertise |
| 1:48.8 | their product. They just want you to run ads and I've never been into that. I've |
| 1:52.4 | always been into talking about my experiences |
| 1:54.4 | and sharing solutions for the field and speed clean has been a great partner in that. |
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