Reply. Things can get ugly fast! The fuse is downstream from a transformer. Which wire on my transformer to do install the 5 amp fuse for low voltage . I noticed it blew when I switch from heat to AC, but now, it just blows within minutes when I put the fuse in. Hi, I am trying to build a 5VDC from my 220VAC (Switched-mode power supply). HVAC … The first step is to convert AC-DC. Thermistor is MF72-5D9 Surge Current Limiting. Click to expand... this is a straight ac . Much like having a dirty air filter, this could cause your air conditioner to blow a fuse simply from overworking. There are many possible reasons for AC fuses to blow, and sometimes they are connected. When I turn on the power, F1 blows immediately. Replacing the fuse or resetting the breaker can temporarily fix the problem, but if the underlying issue is not fixed, the fuse will just blow again. You may also cut off the REV valve low-voltage wire. Here is a list of some of the most common reasons: Old or Blocked Motor; An old or blocked motor causes the capacitor to work over-time. I ran through a checklist that came with my furnace and found that the low voltage fuse had burned up. Open a low voltage DC circuit (like when you blow a fuse) and there will be a small arc. most the low voltage shorts are in the side door access on Tranes, either against the grill, or a tube. Fuse keeps blowing on AC/DC Adapter. Ask Your Own HVAC Question. Hello. Any ideas. Last. What causes a blown fuse at the low voltage transformer in ac unit? Exact same problem. wmodavis. I have an outside A/C compressor and indoor furnace fan combo in the attic. These fuses are suitable for low-voltage automotive and other electronic applications. The current rating of a fuse is the current that it can carry for indefinite time periods without opening. Without the proper amount of refrigerant, your AC has to work harder to maintain its performance. Active 11 months ago. 1; 2; Next. I replaced the fuse and used the thermostat to turn the fan on followed by the heater then the A/C. a) the fuse blows: The fault is in PSU b) fuse doesn’t blow = the short causing the fuse blowing is DEFINITELY between the power socket on the back of the Mac, and the PSU. He told me that he has seen when low voltage had caused a fuse to blow or breaker to trip (in high voltage machines). By the way, would you be so kind as to post a really good close up image of this area of the PSU. V1 is 220VAC, the peak is about 300V. I even installed a new t-stat. The Military standard for Fuses; MIL-PRF-23419 does not seem to differentiate between AC or DC voltages for low voltage fuses.-- From Military sources Voltage rating. What could be the problem? Have a specialty? Answer: I have encountered this problem several times.Most of the time the problem ends up blowing the fuse on the control board, (if your control board has a fuse) instead of the transformer. An over-sized fuse will allow too much current to flow. Low voltage fuse blowing in furnace. Above is my schematic. Show More. It burned up immediately. The voltage rating relates to the ability of the fuse to function and extinguish internal arcs when it opens. Now it will run for about 60 secs, shut off, start again and keep repeating that cycle. Graphics in this document are for representation only. hvac1000 Posts: 14,540, Reputation: 435. Join Date: Dec 2004. C1 and C2 are the same, each has 200V voltage max rating. Users who viewed this problem also viewed: prinaudo. Max. Fast-acting fuses open circuits quickly when surges are detected. Viewed 33k times 1. If not, you need to replace the IC, and I wouldn't bother trying to repair it. Is this a heat pump, or straight A/C. I ran through a checklist that came with my furnace and found that the low voltage fuse had burned up. This small part helps to regulate the electrical current as it flows … I'm out of fuses - LOL and before I call the tech back out, I'm trying to get some answers.. My AC stopped working during the night last night. Blowing low voltage fuse breaker trip control wiring troubleshooting ive got a 5 amp fuse that keeps popping on a circuit board. Show Less. I installed a new fuse, and it burned up immediately. 1; 2; Next. Low voltage: Check that nameplate voltage is maintained. This is where the problem lies. Jump to Latest Follow 1 - 20 of 22 Posts. 4 years ago. Check overload relay, stator and push buttons: Motor runs and then dies down: Power failure: Check for loose connections to line, to fuses and to control: Motor does not come up to speed: Motor is applied for the wrong application To protect your family and ensure your furnace keeps working as it should, you need to find the source of the problem. If the fuse is blown or the low-voltage breaker is tripped, as will generally be the case in a short, first replace the fuse, or, better yet, use a test breaker, like the Supco Pro Fuse (in place of the fuse while testing) to eliminate wasting fuses. Apply to be an Expert. Fuses are essentially classified into several types which are based on the application namely AC type fuse and DC type fuse. Member. ac keeps blowing the 5 amp fuse. Rheem ac troubleshooting keep blowing the 3a fuses now starts and shuts off. 5-Amp fuse keeps blowing on AC. Answered in 2 minutes by: 2/25/2011. It burned up immediately. This defeats the purpose of using a fuse as a safety device. Ran orange from thermo to heat pump then the red yellow from thermo to air handler to heat pump. Post to Facebook . Go. Problem: My 24 volt low voltage transformer continues to burn up.This is the second transformer. The capacitor is important because it helps run the cooling system, known as the condenser . This is one reason that re-wireable fuses are no longer allowed under NEC. I assumed it was the low voltage wiring from the wall t-stat to the control board so I got new wire and ran up to the attic. Open circuit: Fuses blown. And again these are further classified into various kinds based on the voltage levels. Disconnect the compressor contactor; Once you disconnect the compressor contactor, set thermostats to cooling mode and tape off the low voltage wire to restart. It kept blowing the 3a fuse immediately when attempting to start; so I replaced it with a 5a fuse. Fuses aren't rated for voltage carrying purposes, the rating come into effect when and if the fuse blows, you do not want a low voltage rated fuse on a high supply, the construction of which may allow conduction after blowing. Level 1 (Contributor) 1 Answer: 1. Use with Fuse Blocks for Automotive Fuses. Low voltage fuses have a voltage rating of less than or equal to 1,500V. Location: San Jose,Ca. Open a high voltage DC circuit (like when you blow a fuse) and there will be a huge (long) and super hot arc (spark). I have a rheem classic 90 plus heating and air unit. Low voltage fuses are defined as fuses with a voltage rating less than or equal to 1,500V. Some CBs also perform switching function with or without current flowing in the circuit. Post to Twitter . Low refrigerant. Once of my customers had a similar problem last week. Another cause of blown AC fuses could be a low refrigerant level. this video shows what a low voltage fuse looks like in an air handler. Joined Oct 23, 2010 739. Breakthrough current, labeled on the fuse as IR, is the maximum current that a fuse can safely stop in the event of a short circuit. AC works fine but as soon a I switch to heat the fuse blows. So, I disconnected all thermostat wires from inside the furnace and installed a new fuse. So at low voltage say 12 volts there is not much tendency to arc across the gap when the fuse blows but at 240 volts or higher the arcing becomes quite significant. Thanks for any insight you can help provide. Rated Voltage AC 500V* / DC 440V upto 630A (DC 250V for size 00) AC 690V/DC 440V (DC 250V for size 00) Rated Current Range 2A-800A, AC 500V 40A-500A, AC 690V Rated Breaking Capacity AC 120kA / DC 25kA Mounting position as desired but preferably vertical Resistance to climate -30°C to +50°C at 95% relative humidity HRC fuse is the fuse element of high-grade copper. Ask Question Asked 5 years, 1 month ago. Select a fuse In three simple steps. Last. The unit was off and the 3 amp fuse was blown. Like Reply. Subscribe me. Go. A circuit breaker also does similar type of function as a fuse. Sponsored Links #2 10-28-09, 05:15 PM M. mbk3. Answers and Replies Related Electrical Engineering News on Phys.org. Low-voltage high rupture capacity (HRC) fuses are used in the area of main distribution boards in low-voltage networks where there is a high prospective short circuit current. Check connection. Is there any situation at all that this would be true? 1 - 20 of 22 Posts. Ask Question Asked 3 months ago. The following diagram clearly depicts the electrical fuse types chart depending on the AC fuse and DC fuse. Fuses are available in AC and DC circuits from extra low voltages to high voltages. Just had one yesterday- sov wire rubbing the louvered door on side of unit. Low voltage fuses are very common in electrical systems and they come in diverse styles, shapes and sizes. Save Share. Fuses are rated by current, voltage, breaking capacity (interrupt capability) and whether they are designed to operate on AC or DC circuits. 1 of 2 Go to page. Out the door I ended up paying $51 for the contactor relay and DCB another $36 for the solenoid coil (all replaced by me) then $49 for the service call and $100 for the Low Voltage Wiring Repair. The 5 amp fuse is on the low voltage side, so its not the blower motor causing it to blow. Ended up getting a "free" transformer out of the deal but all together spent a grand total of $236 and my heat is working again with no famous blown 3 amp fuse. HELP!!! My AC stopped working during the night last night. Any help would be appreciated. Col 3:23 questions asked, answers received, ignorance abated. I let the unit run the A/C. High rupture capacity fuses may be rated to interrupt current of 120 kA. If there's no AC voltage on the transformer, check the gate of the MOSFET: if there's a PWM signal there, the SMPS IC is still alive, and replacing the FET can bring the PSU back to life. 1 of 2 Go to page. They are generally larger than screw-type fuses, and have ferrule cap or blade contacts. Share this conversation. The fuse is downstream from a transformer. small nick in wire, but enough to blow fuse. It was a bad cooling contactor coil. In the event of a short circuit the fuse blows cutting power and stopping wires melting. 0 Why is my trans blowing on the primary? I installed a new fuse, and it burned up immediately. A fuse is an inexpensive device that can carry only a certain amount of current. Low voltage fuses are very common in electrical systems and they come in different shapes and designs. It is really making me curious. And in article electrical wiring diagrams for air conditioning systems part one i explained the following points. Types of Fuses. So, I disconnected all thermostat wires from inside the furnace and installed a new fuse. If the arcing melts more of the wire no problem because the gap gets bigger, but if the wire melts to the ends and the arcing continues until there is an arc between the caps then you have a fire in the fuse box. When a fuse is in an electronic circuit and the current exceeds the rated level, the fuse melts (blows), thus breaking the circuit and preventing the excessive current from flowing. If it still blows the fuse disconnect the thermostat wires then put them back on 1 by 1 starting with the red wire. 3 amp fuse keeps blowing on my ac unit i checked the wiring… 3 amp fuse keeps blowing... 3 amp fuse keeps blowing on my ac unit i checked the wiring form the in door unit to the outside unit and no shorts any sugestions. Unlike a circuit breaker, fuse is self-destructive which requires replacement after it disconnects a circuit. The use of fuses in a circuit provides cheap insurance should there be an accidental or unintentional fault in the system wiring or components. Yes, if you have a few extra fuses. Using the correct fuse is important because a undersized fuse can stop circuits operating by cutting power at low currents. 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