Singlecoil Posted July 7, 2004 Share Posted July 7, 2004 Does anyone know what wattage the resistor block resistors are rated at? Someone mentioned that they were 1 ohm each and that tests correctly for the one I have left. My local electronics store has ceramic covered 5 watt ones for 50 cents each. I broke off the ceramic coating and revealed the coiled resistor that looks similar to the OEM ones. Unfortunately, they only had .8 ohm, and 1.2 ohm. It seems to me that the .8 one would make the fan turn slightly faster than a 1 ohm and the 1.2 would make it turn slightly slower. The .8 might operate cooler as it is resisting less current. I'm not sure what the watts has to do with it. Should I get the lowest watts I can find or the highest? A buck is sure a lot cheaper than $60 for a new resistor block. Quote Link to comment Share on other sites More sharing options...
EmmCeeBee Posted July 7, 2004 Share Posted July 7, 2004 I'm stepping on thin ice here cuz I don't know about these resistors in particular -- never had to replace them. And electronics isn't my day job..... >> they only had .8 ohm, and 1.2 ohm. .... The .8 might operate cooler as it is resisting less current. Actually, that's backwards. The .8 ohms would draw more current. The relative equations are: I = V/R and Power = V*I . What we don't know here is the resistance of the fan motor, which would be in series with the resistor block. (So a 1 ohm resistor + blower motor won't draw a full 12 amps.) But in any application, it's always safer to over-design and use a resistor that's rated for more watts. The tradeoff may be cost and size. I did the same thing in an old Plymouth, years ago, so it's possible. Might consider rigging it up so the resistor is exposed at first, so you can see how hot it gets. Hope this helps. -- Mark Quote Link to comment Share on other sites More sharing options...
SubSandRail Posted July 7, 2004 Share Posted July 7, 2004 The wattage rating tells you how much power it can dissipate (turns it to heat) without damaging the resistor, so the higher the rating the better up to a point. Most engineers specify a wattage rating 1.5x to 2x higher than the peak load. A bullet-proof method of getting the resistance you want and spreading out the heat would be to use two of each as shown on the attachment. When you use the 5 watt resistors, you need to remember that they assume that you will place them where they will get good air flow over them; or you will stick them on a chunk of metal with thermal grease or thermal glue. The heat still has to get out. If you dissipate 1 watt in a 5 watt part in a vacuum, it will burn up because you did not provide a path for the heat to get out (don't laugh, NASA did it to one of my parts). Quote Link to comment Share on other sites More sharing options...
edrach Posted July 7, 2004 Share Posted July 7, 2004 Try doing a search on this; it's a topic that's been covered numerous times. If I remember correctly the resistors are in the neighborhood of 50 watts; seems about right since the originals are open coils sitting directly in the air flow from the blower. The wattage rating tells you how much power it can dissipate (turns it to heat) without damaging the resistor, so the higher the rating the better up to a point. Most engineers specify a wattage rating 1.5x to 2x higher than the peak load. A bullet-proof method of getting the resistance you want and spreading out the heat would be to use two of each as shown on the attachment. When you use the 5 watt resistors, you need to remember that they assume that you will place them where they will get good air flow over them; or you will stick them on a chunk of metal with thermal grease or thermal glue. The heat still has to get out. If you dissipate 1 watt in a 5 watt part in a vacuum, it will burn up because you did not provide a path for the heat to get out (don't laugh, NASA did it to one of my parts). Quote Link to comment Share on other sites More sharing options...
Singlecoil Posted July 8, 2004 Author Share Posted July 8, 2004 Ok, my bad. I did the search before I posted this but got frustrated at all the links that went nowhere. After it was suggested I search again, I found the archived thread with all the good info (perhaps too much). I elected to tap into the mad scientist in myself and tackle this dilemma feet first. I found some 5 watt ceramic coated resistors and decided to wire them in parallel, as SubSandRail suggested, to keep the temps down. One of my OEM resistors, the one for fan position three, was intact. I needed only to fix the ones for position one and two. I was shooting for .9 ohms for position two, and .7 ohm for position one. I purchased two 1.8 ohm resistors, and couldn't find two 1.4 ohm so I ended up with two 1.2 ohm units for fan position one. Wiring them in parallel would halve those ratings, yielding .9 and .6 respectively. The first order of business was to take a hammer, and smash the ceramic coatings off. They were too bulky, and I thought they would not let the resistors cool fast enough in the airflow. Here's one of each of the resistors (I used two of each). Then I soldered them in parallel, and soldered them into the resistor block. I plugged them in, held the block in my hand and turned on the fan. In position three, the OEM resistor got hot enough to glow. When I held it up to the airflow, however, the glowing ceased as it cooled rather quickly. The same for my two in position two. The glowed pretty good, but didn't under the airflow. Position one didn't glow much at all. There is a metal casing they mount into in the air duct, so with that and the airflow of the fan, I'm not too worried about it. Of course, the wife has instructions to immediately select position four if she smells anything burning. How much am I saving on this? Is it worth the headache? I'm not sure at this point. The resistors cost $2.00 total, so that saved about $62.00. The block is easy to get to thanks to the awesome photo I found on this site. I can tell I'm going to be spending a lot of time here. Here is a photo of the finished, soldered project. I had to twist the resistors I fashioned into a more diagonal orientation to get them to fit inside the stock duct opening. Of course, do this at your own peril. Quote Link to comment Share on other sites More sharing options...
edrach Posted July 8, 2004 Share Posted July 8, 2004 Nice piece of work! This one should go into the archives! Also, the exact resistance isn't critical since the fan goes slow, medium, and fast; it doesn't care about more slow or more medium, etc. You did save a bundle; I believe the assembly is around $70 from the dealer, maybe more. I usually pull them in the wrecking yards but only 1 in 10 is okay enough to pay the $5 for the good one. Plus sometimes they are a pain to pull since moisture gets into some of the small screws and they rust in place. I'm not surprised at the resistors glowing; I do think the 50 watts is pretty accurate; if the voltage isn't going to the blower, the voltage has to be disappated somehow. Quote Link to comment Share on other sites More sharing options...
Singlecoil Posted July 13, 2004 Author Share Posted July 13, 2004 Update. The resistors in position two failed in about 2 hours. I replaced them with a different brand, but still 1.8 ohm 5 watt resistors. The NTE resistors are of a larger diameter once the ceramic is removed, and will (I hope) dissipate the heat better. They look like this: (Pictured is a 1.2 ohm but the 1.8's look the same) Quote Link to comment Share on other sites More sharing options...
edrach Posted July 13, 2004 Share Posted July 13, 2004 If you have access to nichrome wire, you could wind your own resistors and have plenty of power dissapation. I just haven't spent the time or effort to follow up on that option. Quote Link to comment Share on other sites More sharing options...
Singlecoil Posted June 15, 2007 Author Share Posted June 15, 2007 UPDATE! Three years later (almost) this rebuilt resistor block is going strong with the NTE resistors shown above. I broke off the ceramic coating, though I'm not sure if that was required, and soldered them in as shown in the other picture. One bit of advice: After I soldered the second batch, I did not turn the fan on until they were reinstalled in the housing so they would have immediate cooling. They will glow rather quickly without airflow. I don't know if that is what made the first batch fail quickly or if the different brand of resistors didn't work as well. I suspect they were just not the same quality as the NTE ones. Quote Link to comment Share on other sites More sharing options...
edrach Posted June 15, 2007 Share Posted June 15, 2007 UPDATE! Three years later (almost) this rebuilt resistor block is going strong with the NTE resistors shown above. I broke off the ceramic coating, though I'm not sure if that was required, and soldered them in as shown in the other picture. One bit of advice: After I soldered the second batch, I did not turn the fan on until they were reinstalled in the housing so they would have immediate cooling. They will glow rather quickly without airflow. I don't know if that is what made the first batch fail quickly or if the different brand of resistors didn't work as well. I suspect they were just not the same quality as the NTE ones. You discovered the secret of the resistor block; even with the original resistors which are pretty high wattage, the airflow from the blower is needed to cool them. And the higher the speed, the more air flow to keep them from burning up. Good work. Quote Link to comment Share on other sites More sharing options...
Pineridge Posted November 12, 2007 Share Posted November 12, 2007 I just tried this fix and it passed (so far) with flying colors. I used one resistor @ .50 OHMS. If it fails I will update but until then thanks for the help!!! Quote Link to comment Share on other sites More sharing options...
edrach Posted November 13, 2007 Share Posted November 13, 2007 I just tried this fix and it passed (so far) with flying colors. I used one resistor @ .50 OHMS. If it fails I will update but until then thanks for the help!!!Congratulations to someone who must have used the search function to find a 3 year old thread and solve a problem. Quote Link to comment Share on other sites More sharing options...
msteel Posted November 13, 2007 Share Posted November 13, 2007 For the next guy searching, there are aftermarket resistors available for considerably less than the dealer. Standard Motor Products makes one that is currently available at rockauto.com for around $25. A bit more expensive, but a bit easier. Quote Link to comment Share on other sites More sharing options...
YnotDIY Posted November 5, 2019 Share Posted November 5, 2019 Did this repair today. Worked like a charm. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.