hvac1000 Posts: 14,540, Reputation: 435. Join Date: Dec 2004. In the event of a short circuit the fuse blows cutting power and stopping wires melting. They are generally larger than screw-type fuses, and have ferrule cap or blade contacts. Is this a heat pump, or straight A/C. 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. Open circuit: Fuses blown. Open a low voltage DC circuit (like when you blow a fuse) and there will be a small arc. So, I disconnected all thermostat wires from inside the furnace and installed a new fuse. AC works fine but as soon a I switch to heat the fuse blows. Show Less. Go. I replaced the fuse and used the thermostat to turn the fan on followed by the heater then the A/C. The current rating of a fuse is the current that it can carry for indefinite time periods without opening. It burned up immediately. Last. wmodavis. Ask Question Asked 5 years, 1 month ago. Low voltage fuses are very common in electrical systems and they come in diverse styles, shapes and sizes. Low voltage fuses are very common in electrical systems and they come in different shapes and designs. 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. It burned up immediately. 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. Answered in 2 minutes by: 2/25/2011. Once of my customers had a similar problem last week. 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. Click to expand... this is a straight ac . Viewed 33k times 1. Fuses are available in AC and DC circuits from extra low voltages to high voltages. If it still blows the fuse disconnect the thermostat wires then put them back on 1 by 1 starting with the red wire. Fuses are rated by current, voltage, breaking capacity (interrupt capability) and whether they are designed to operate on AC or DC circuits. My AC stopped working during the night last night. This is where the problem lies. 1 of 2 Go to page. This small part helps to regulate the electrical current as it flows … I ran through a checklist that came with my furnace and found that the low voltage fuse had burned up. this video shows what a low voltage fuse looks like in an air handler. A circuit breaker also does similar type of function as a fuse. Thermistor is MF72-5D9 Surge Current Limiting. Graphics in this document are for representation only. Using the correct fuse is important because a undersized fuse can stop circuits operating by cutting power at low currents. 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. Share this conversation. Now it will run for about 60 secs, shut off, start again and keep repeating that cycle. Problem: My 24 volt low voltage transformer continues to burn up.This is the second transformer. It was a bad cooling contactor coil. ac keeps blowing the 5 amp fuse. This defeats the purpose of using a fuse as a safety device. These fuses are suitable for low-voltage automotive and other electronic applications. When I turn on the power, F1 blows immediately. Is there any situation at all that this would be true? Subscribe me. HVAC … The following diagram clearly depicts the electrical fuse types chart depending on the AC fuse and DC fuse. And again these are further classified into various kinds based on the voltage levels. I have an outside A/C compressor and indoor furnace fan combo in the attic. Rheem ac troubleshooting keep blowing the 3a fuses now starts and shuts off. Low refrigerant. A fuse is an inexpensive device that can carry only a certain amount of current. Ask Question Asked 3 months ago. Without the proper amount of refrigerant, your AC has to work harder to maintain its performance. Answers and Replies Related Electrical Engineering News on Phys.org. Fuse keeps blowing on AC/DC Adapter. This is one reason that re-wireable fuses are no longer allowed under NEC. Level 1 (Contributor) 1 Answer: 1. Low voltage fuses have a voltage rating of less than or equal to 1,500V. Post to Twitter . Just had one yesterday- sov wire rubbing the louvered door on side of unit. I even installed a new t-stat. 1 - 20 of 22 Posts. Hi, I am trying to build a 5VDC from my 220VAC (Switched-mode power supply). Types of Fuses. The fuse is downstream from a transformer. High rupture capacity fuses may be rated to interrupt current of 120 kA. Thanks for any insight you can help provide. The first step is to convert AC-DC. What causes a blown fuse at the low voltage transformer in ac unit? Above is my schematic. I installed a new fuse, and it burned up immediately. Hello. Member. Low voltage: Check that nameplate voltage is maintained. My AC stopped working during the night last night. Jump to Latest Follow 1 - 20 of 22 Posts. Joined Oct 23, 2010 739. 0 Why is my trans blowing on the primary? Last. Open a high voltage DC circuit (like when you blow a fuse) and there will be a huge (long) and super hot arc (spark). 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). Low voltage fuse blowing in furnace. By the way, would you be so kind as to post a really good close up image of this area of the PSU. Disconnect the compressor contactor; Once you disconnect the compressor contactor, set thermostats to cooling mode and tape off the low voltage wire to restart. Any help would be appreciated. The unit was off and the 3 amp fuse was blown. 1; 2; Next. The capacitor is important because it helps run the cooling system, known as the condenser . 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. 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 If not, you need to replace the IC, and I wouldn't bother trying to repair it. 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. Fuses are essentially classified into several types which are based on the application namely AC type fuse and DC type fuse. 1 of 2 Go to page. Blowing low voltage fuse breaker trip control wiring troubleshooting ive got a 5 amp fuse that keeps popping on a circuit board. Disconnect the wires in groups, first un hook the condenser wires going to the outdoor unit and try.. The 5 amp fuse is on the low voltage side, so its not the blower motor causing it to blow. Go. Users who viewed this problem also viewed: prinaudo. Active 11 months ago. 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. Max. Apply to be an Expert. Have a specialty? C1 and C2 are the same, each has 200V voltage max rating. Like Reply. To protect your family and ensure your furnace keeps working as it should, you need to find the source of the problem. Much like having a dirty air filter, this could cause your air conditioner to blow a fuse simply from overworking. Low voltage fuses are defined as fuses with a voltage rating less than or equal to 1,500V. 1; 2; Next. 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. I noticed it blew when I switch from heat to AC, but now, it just blows within minutes when I put the fuse in. It is really making me curious. 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 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. Which wire on my transformer to do install the 5 amp fuse for low voltage . Exact same problem. I'm out of fuses - LOL and before I call the tech back out, I'm trying to get some answers.. small nick in wire, but enough to blow fuse. I ran through a checklist that came with my furnace and found that the low voltage fuse had burned up. I installed a new fuse, and it burned up immediately. 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. Show More. Post to Facebook . And in article electrical wiring diagrams for air conditioning systems part one i explained the following points. 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. Ask Your Own HVAC Question. Another cause of blown AC fuses could be a low refrigerant level. Some CBs also perform switching function with or without current flowing in the circuit. most the low voltage shorts are in the side door access on Tranes, either against the grill, or a tube. Check connection. You may also cut off the REV valve low-voltage wire. There are many possible reasons for AC fuses to blow, and sometimes they are connected. Things can get ugly fast! An over-sized fuse will allow too much current to flow. 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. Save Share. 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. Reply. Fast-acting fuses open circuits quickly when surges are detected. Unlike a circuit breaker, fuse is self-destructive which requires replacement after it disconnects a circuit. 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. HELP!!! So, I disconnected all thermostat wires from inside the furnace and installed a new fuse. I let the unit run the A/C. 4 years ago. Select a fuse In three simple steps. Use with Fuse Blocks for Automotive Fuses. Any ideas. Location: San Jose,Ca. Yes, if you have a few extra fuses. The fuse is downstream from a transformer. Sponsored Links #2 10-28-09, 05:15 PM M. mbk3. What could be the problem? V1 is 220VAC, the peak is about 300V. I have a rheem classic 90 plus heating and air unit. The voltage rating relates to the ability of the fuse to function and extinguish internal arcs when it opens. Ran orange from thermo to heat pump then the red yellow from thermo to air handler to heat pump. Col 3:23 questions asked, answers received, ignorance abated. It kept blowing the 3a fuse immediately when attempting to start; so I replaced it with a 5a fuse. 5-Amp fuse keeps blowing on AC. 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