A Low Voltage Short That Has Stumped Me

[@HVACGUY]

I was up front with the customer about what I found, and likelihood of fixing the problem, and was given the okay to move forward. I decided to show this because I’m not perfect, and sometimes finding the exact problem may be difficult.

[@JesseDoesHVAC]

The first step to living a career of integrity is the ability to admit your own fallibility Theres only so much you can do sometimes as long as you let them know beforehand

[@lookgd]

sheeesh other than the Compressor outside of it's Service Life (Megger the Compressor) or Contactor/Xfrmer faulty/back feeding or low-voltage placement (wires put together incorrectly)... Id say, it's Option Z: Hackjob Harry made an appearance, and poof, they are gone. Now, You're here to fix it. Living the Dream, bruh. 🎉

[@kristoforcowden2910]

Only a suggestion if called back again. Check your voltage coming in. I've found if your voltage is above 247 that can be an issue.

[@ozoneair6632]

I had a low voltage problem back I the summer on a carrier heat pump and it was the defrost sensor shorting.

[@timrob0420]

I installed a Rheem heat pump and air handler at a dentist office about three years ago. Every winter. I get a diagnostic call, go there and low voltage fuse in air handler is blown. Replace fuse, spend about two hours hunting for rub outs and testing the low voltage coils of all components only to find nothing. Then, rest of winter the fuse never blows again. Everything is great, runs great, works great, all through rest of the year into spring summer and fall. Then, winter rolls around and same thing. I’ve been stumped on this elusive once in a blue moon short for three years now.

[@melquesedekcastro7480]

In your situation I would measure the low voltage total amps consumption for the cooling and then do the same for the heating cycle and "see" what is the difference in amps consumption between both cycles. Maybe, the total power consumption on the circuit is too close to the fuse limit. In the situation in this video I wish he had measured the low volts from the transformer, because he got 16 ohms resistance for the contactor and he also got 14 Ohms in the reversing valve and whenever both of them are energized at the same time if the lower volts is more than 29V we have a total amps of more than 3.5 Amps. Maybe that's the problem, I am saying maybe.

[@MrAdamd83]

On heat pumps always check the pressure switch wires for rub points

[@twolfe4295]

I've put these stats in and if there is a short they will burn out and do crazy things. The T6 stats are sensitive.

[@ThierryC2373]

That thermostat was for sure an antique!!!

[@astateato]

LOVE your vids!!!

[@HVACGUY]

I appreciate that

[@jimoliver5758]

Feel your pain. Hate calls like that. I struggle on getting paid for my time that spend on them

[@Chainsaw600]

I had one like this not long ago. Drove me nuts chasing the short. I was about to give up until the homeowner said that her son had replaced the thermostat just recently. I asked how long ago and she said at the beginning of summer. It worked fine in cooling but popped with heat strips. The son didn’t set up the thermostat correctly. He thought every thermostat was identical and didn’t bother to program or check the instructions. Lesson learned was to ask if they had done anything to the system recently. I would have been there 15 min vs. 2 hours!

[@kens.3729]

Only one (1) person doesn’t make any Mistakes and I don’t know anyone who has ever met him. We can Talk to him and he’s a Great Listener. 👍🙏

[@catwrangler1613]

I can't believe they are still running an antique t-stat that belongs in a museum. All the money they would save on electricity as well saving runtime on the equipment. Also, I would install a 75va transformer with resetable over amp protection. Then see if u get another call back.

[@tedhicks5431]

Bad wire under house may be bad rats one of those crazy calls . That dog was driving me crazy

[@kevonslims7269]

I so wanted you to go thru the crawl space and check that low voltage for damage or animals biting into it..

[@Eddy63]

My money's on the new T-Stat solving the problem ... Nice van by the way ...Thx ...

[@DevinHVACInc]

I saw someone comment abt putting fuses on different circuits. I used to work at car dealership before doing ac work. We would put LED lights on circuits that would cause a particular issue that we couldn’t find at the time. When it happens, the customer will look and see which light is out and we would then trouble shoot that part of the circuit. Maybe that’s a suggestion for this sys.

[@hillside7077]

We use tattletails

[@firstnamelastname5330]

Isolate the circuit, use a toner, check any relays or switches to make sure they are working correctly in the normally open or closed position, if you keep blowing fuses and cant gind the short or ground its most likely a bad capacitor!

[@rickharper1497]

I would have probably changed the thermostat after second or third visit. Why it wasn't updated when unit was installed?

[@joseorta9928]

Dammmmm Dogs!!!

[@davidkraft3690]

We feel your frustration ! Look forward to a follow up on this service call.

[@jorgejanicas8289]

I am pretty sure the issue is resolved now that the mercury type tstat has been replaced. I suspect that a surge current that exceeds the rating of the fuse and not a ground fault is the cause. The spark you observed may have been the circuit being made when the mercury tilted over in one direction and then the other direction breaking the circuit. This may be the cause of an inrush current that exceeds the fuse rating and thereby blowing the control fuse. I have observed a mercury type tstat make and break a circuit quickly at the control point and believe this may be the cause of your intermittent issues with blown fuses. Keep them coming, I really enjoy your videos.

[@RoyArmy-WREW918]

I was also thinking that is not always a short, but a surge, being an Electronics Technician myself ...for what it's worth.

[@throttlebottle5906]

the spark when switching would be due to back EMF of the contactor coil and any other relays in the system. back EMF high voltage surge happens when the magnetic field of the coil collapses. the voltage peak could reach a few hundreds volts. it's possible them switching it fast with system running is surging the fuse with a high current and voltage pulse, but there's probably a wire rubbed out somewhere and intermittent shorting or maybe contactor not always pulling in fully(it should be buzzing then), that can cause higher current draw, but usually burns out the coil.

[@mrautoguy8419]

What brand bag you have?

[@JesseDoesHVAC]

Hey Curtis, do you have an analogue megohmeter? Something like the Kyoritsu megs, ive got one and its come in handy especially when the digital meter isnt plating ball

[@bruce8572]

I've had those old Honeywell t-stats get worn, and short out transformers. Good idea to change out the t-stat.

[@sknight0391]

Ol' Sparky ⚡⚡⚡

[@dell982]

heat pump 99% pres. switch wire rubbing metal somewhere in unit

[@davidgilpin5200]

I had an intermittent short in our low voltage traditional POTS phone wiring. Would work fine for months, then the phone in the kitchen would have no dialtone... Finally figured out that the rodents had chomped on the wires near the soffit in the attic and that was causing the intermittent short. If this thing continues to drive you batty, replace the LV run to the condenser.

[@leviramirez7873]

Gotta love the intermittent low voltage short.

[@kens.3729]

I hope you charged the Customer extra for the crumb snatcher(s) that never let up in the barking department. 🤔👎

[@orionwarren4244]

That thermostat was ancient. It need to go anyway.

[@rayking1450]

intermittent shorts are very, very difficult to find. I feel your pain.

[@ParabellumX]

Those lil yappin ankle-biters make you wanna field goal them across the street sometimes. 🤬

[@iamnoone.]

I wanted to do worse

[@alabamahvacprofessional2946]

Curtis, I feel for you, brother. I have been in the industry for 40 years, and have seen some crazy stuff. Question? Does it only blow the fuse in cool mode? All types of solenoid valves when energized pull a lot of current if the spool doesn't immediately shift. I also know that Payne has a design flaw on their package unit high pressure cutout switch wiring. I saw the exact same problem twice last summer.... I would walk up to the unit (not running), and the control board would click every second or two. If you run across that exact situation on a Payne, the wires going to the hpco switch are rubbing against the frame.

[@HVACGUY]

It seems to blow the fuse every few months, normally in the cool mode. But, this ti e of year they coulda been running it in either mode.

[@MariosACandRefrigeration]

MAYBE checking sequenser resistance.and behind def board for lizard.disconnect 24v wires at AHU and condenser and check to common for resistance.very interesting.thanks for sharing.

[@TrashPanda2088]

what is the light that you use that sicks, I need that it would help big time?

[@HVACGUY]

Milwaukee battery light. Bought at Home Depot

[@lancelawrence3259]

Nice work

[@jme36053]

If not the carefully inspected wiring causing the issue then where the wiring terminates must be the cause. Replacing the t-stat is one of the least costly pro-active steps to take.

[@Bikofree2]

Sorry I had to turn it off I can't take the dogs barking. Other than that I love your videos

[@kennethharris2445]

Definitely would have started upstairs near air handler and used resettable fuse and used process of elimination by unhooking one low voltage wire at a time when resettable circuit breaker pops I know precisely where to look

[@HVACGUY]

That’s what I’ve done in the past. And nothing would make it blow, nothing. Whatever was happening was intermittent

[@iamnoone.]

I lost half my brain cells from that dog yapping. It's like chalk on a chalkboard

[@Knight805]

1960 called, they want their T-stat back. 😂

[@bobboscarato1313]

That old reliable Honeywell Stat without time delay. Had to install one by outdoor unit!

[@stephenbierlein2517]

Mercury and biemetal stat all spark under load when bounced . You don't see electronic stats but happens too. Same when heat to cool if there's a load on . The switches will spark . Just don't see because of cover .

[@hinspect]

Of all things electrical, intermittent is what I have always hated the most! That new thermostat will sure cure people from switching back and forth between heat and cool! I was doing an unrelated service on a rental house and there were two teenage girl sisters that had separate bedrooms. One girl would emerge from her room and adjust the thermostat to cool, then slam the door. Then the other would do the same except switch it to heat. Even the Dad had his ass locked in his room! Drove me nuts! I yelled instructions about ruining the system and thank goodness they didn't screw up the heat pump! Thanks for the video and looking forward to see what you find out. 👍🇺🇸 (Heat gun on the circuit boards?)

[@nsacrooks]

I'm in pain watching you search for a short that does not exist when you are looking for it. Here is the solution. Insert more 3a or 4a fuses all about the system. When you come back the 5a main should be good but a 3 or 4a will be blown. At that point you can replace coils, etc in that area.

[@HVACGUY]

If I go back, that sounds like a plan.

[@jamesfitzsimmons381]

nsacrooks. Are you saying that if I put 3-4amp fuse on wire from contactor and another fuse on the rev valve coil wire that if the contactor hangs up and draws more amps that fuse will blow but the fuse on rev valve won’t blow. ??? Had never tried that

[@nsacrooks]

@@jamesfitzsimmons381 You are trying to find where the problem is. Maybe putting 4a fuses on the white, green, orange if energized, and yellow leads at the thermostat. Maybe to power in on the defrost board as well. When a fuse blows, shotgun all the parts the fuse supplied.

[@jamesfitzsimmons381]

@@nsacrooks thanks

[@jamesfitzsimmons381]

Hate to say it don’t think anything was wrong with thermostat. I know why you changed it but I think you need to look more at the defrost senser/ wiring. I have seen the sensor metal areas that mount on tubing have shorting spots. We’re you checking ohms to ground with the 24v hot on the wires you were checking??

[@jamesfitzsimmons381]

Curtis was the wires you were checking to ground with the ohm setting on your meter hot/24 volts you were checking the field 24v. When you had pull the molecule plug off the board

[@HVACGUY]

@@jamesfitzsimmons381 yes

[@jamesfitzsimmons381]

@@HVACGUY sorry to keep bothering you. So I can learn from this 1) what were expecting to see on your meter 2). I thought putting volts on the ohm-resistance setting was not good to do. I thought. you only checked the circuits with the power off when checking for grounds/ shorts with meter on ohms

[@bobboscarato1313]

I like dogs barking in the background..!

[@stevencossaboon3237]

Nice work Curtis. Gotta love intermittent problems. They will drive you nuts.

[@gar351]

Good Stuff! I was on one almost exactly like this today. The fuse lasts for about 2 months and then blows for seemingly no reason. The only thing I could find "possibly wrong" was that it was a zone system and the installer used the primary transformer for power to the zone panel. I added a separate 40va transformer for the zone system. Fingers crossed, lol!

[@robalexander7348]

Hi Curtis, i have my fingers crossed for you, lets hope the new T/stat fixes the fault issue.. I have a " Brivis MPs Climate Control " Gas central heating system here in Australia which has been faultless over the last 23 years, i do have it serviced each 3 years to Brivis recommended service intervals.. 👍 Unfortunatly Gas is becomming expensive now in Australia 👎

[@ericschwarz9718]

That dog will drive me nuts

[@JesseDoesHVAC]

I know! I think theres two! I recently fit off internal ceiling linear slot grills in a house that had over 30 of them specced out for the whole place. The owners left their chihuahua in the “dog room” and the entire two days spent fitting off the grills and commissioning that dog would not stop! Old head phones in with ear muffs did the trick

[@williamserver4332]

This is a pain in the butt.

[@TPINSC]

I don't know if that's going to fix the problem but I would have probably done the same thing. A sparking stat is not unusual in fact I would expect it but You've got to start somewhere. Please let us know IF that fixes it.

[@jthonn]

Wow what a brain scratcher. I hope that does the trick, but those type thermostats are notorious for making sparks like that. Instead of Payne, that one is a pain. Anyhow, I hope you got it, it needed a new thermostat regardless, nice work. The customer needs to vacuum that air return cover.

[@BrettWae]

Low voltage shorts can be a btch to find sometimes.

[@JohnCline]

Umm, looks like a title typo, it's spelled "stumped." Fortunately, that's easy enough to change.

[@mwdub02]

I usually isolate my board from other circuits with contactors and a transformer. It worked well for me. This way I would rule out the board if my other fuse is blown. I hate these calls when the problem isn’t obvious but we know it’s there. Best of luck 🤞

[@jamesfitzsimmons381]

My old shitty boss would send out a different technician if you didn’t find a intermittent problem. Which would make feel bad it’s one thing you send a another tech if the problem was present and you can’t fix it vs a intermittent problem that’s not present when you arrive

[@HVACGUY]

It’s hard for you to learn that way.

[@jamesfitzsimmons381]

@@HVACGUY he didn’t mine making you feel bad The original tech would know what was already checked. I agree about the learning lesson missed. He only cared about how much can you make today

[@ronroberts7566]

That appeared to be an older style mercoid (mercury bulb) thermostat. The spark is just the breaking of an electrical circuit under load, you saw it because you pulled the cover off. Same as pulling you alligator clips off a load. Sorry but insufficient justification to replace a stat, it may create other calls because customer may have a steep learning curve to understand use, you added now a variable to the situation,

[@woodystokes1543]

Shorts 😅can be frustrating 😊😊

[@JohnSmith-ug5ci]

Those mercury switches ALL spark under load. You are throwing unnecessary parts at the customer. You should not charge him for that part since there was not anything wrong with it.

[@HVACGUY]

I made customer fully aware of the fact that it may not work. And they know if I’m wrong, I’ll make it right. I’m not perfect, and don’t pretend to be. With that said you may be right.

[@JohnSmith-ug5ci]

@@HVACGUY thank you for the reply

[@mikehouser5430]

Place could use a good cleaning

[@felixvara8467]

It’s not the thermostat all mercury based thermostats spark when it closes a circuit 🤭

[@karellodewijks4971]

👍👍😊😊

[@sergioblanco4504]

First

[@jaycrypto-ns7vs]

Quit trying to teach our trade to illegals.