1 00:00:00,000 --> 00:00:07,360 Welcome to the Windshield Chronicles, a mental sequence of operation. 2 00:00:07,360 --> 00:00:12,900 Always refer to your OEM installation and service manuals, but this is a guide on how 3 00:00:12,900 --> 00:00:19,760 5 volt DC communicating systems function and how to troubleshoot them in Daikin equipment 4 00:00:19,760 --> 00:00:20,760 5 00:00:20,760 --> 00:00:27,240 All right, everyone, thank you for joining us on Did You Know?, the ESCO HVAC podcast. 6 00:00:27,240 --> 00:00:32,720 So as part of our Windshield Chronicles, we're going to do a mental sequence of operation 7 00:00:32,720 --> 00:00:35,000 of a communicating system. 8 00:00:35,000 --> 00:00:40,520 In particularly, we're going to talk about the Daikin communicating system that's used 9 00:00:40,520 --> 00:00:43,440 in the residential unitary products. 10 00:00:43,440 --> 00:00:48,880 So when we're looking at a Daikin, this actually falls into play for some of the earlier Goodman 11 00:00:48,880 --> 00:00:53,640 & Manna communicating systems before they went to Comfort Bridge, but it also applies 12 00:00:53,640 --> 00:00:58,200 to the communicating that is going from the indoor to the outdoor, even on the Comfort 13 00:00:58,200 --> 00:00:59,640 Bridge system. 14 00:00:59,640 --> 00:01:06,040 So when we look at the Daikin, the Daikin is using the 5 volt DC communicating platform 15 00:01:06,040 --> 00:01:08,520 that is very common in the industry. 16 00:01:08,520 --> 00:01:12,720 There's other manufacturers that use this same protocol, but we're going to focus on 17 00:01:12,720 --> 00:01:16,780 this Daikin one in particularly, just so you can understand how it's functioning. 18 00:01:16,780 --> 00:01:23,000 So with that communicating system, so say we're working on like a Daikin Fit or any of 19 00:01:23,000 --> 00:01:30,160 the Daikin communicating systems, you're going to have four wires going between the thermostat 20 00:01:30,160 --> 00:01:34,900 and the indoor unit, whether it's air handler or gas furnace. 21 00:01:34,900 --> 00:01:40,760 We're going to have two wires that are going to be a part of the communication network, 22 00:01:40,760 --> 00:01:43,880 and that is number one and number two. 23 00:01:43,880 --> 00:01:49,600 But we also have R and C. Sound familiar, Ty? 24 00:01:49,600 --> 00:01:50,600 Very familiar. 25 00:01:50,600 --> 00:01:55,840 I mean, what would you assume would be on a R and C connection, even if it wasn't a 26 00:01:55,840 --> 00:01:56,840 communicating system? 27 00:01:56,840 --> 00:02:04,000 That's our 24 volt R and C. It's alternating current, 24 volt low voltage back and forth. 28 00:02:04,000 --> 00:02:05,000 Exactly. 29 00:02:05,000 --> 00:02:12,080 And so on this four wire connection, we actually have AC voltage as well as DC voltage. 30 00:02:12,080 --> 00:02:16,620 So from our thermostat, the Daikin communicating thermostat to the indoor unit and from the 31 00:02:16,620 --> 00:02:22,480 indoor unit to the outdoor unit, we are typically only going to use the two wire going outside, 32 00:02:22,480 --> 00:02:25,120 but I have seen applications that use those four. 33 00:02:25,120 --> 00:02:31,520 So if we think about this, let's say that I have my communicating indoor unit, my communicating 34 00:02:31,520 --> 00:02:36,200 thermostat and a communicating outdoor, and I only have two wires going to the outdoor 35 00:02:36,200 --> 00:02:37,520 unit. 36 00:02:37,520 --> 00:02:41,120 And because it would have been on a communicating system, that would have been at least a two 37 00:02:41,120 --> 00:02:44,500 stage communicating, it's probably going to be an inverter. 38 00:02:44,500 --> 00:02:49,560 Do I need 24 volts AC for the control board outside, Ty? 39 00:02:49,560 --> 00:02:53,000 Well, that would be depending on what the manufacturer wanted. 40 00:02:53,000 --> 00:02:55,400 The manufacturer wants that then absolutely. 41 00:02:55,400 --> 00:02:59,360 And if they didn't want that, then I figured those engineers have designed it to where 42 00:02:59,360 --> 00:03:03,440 they are already sealing the high voltage to get that, get that dropped down for their 43 00:03:03,440 --> 00:03:04,920 controls as needed. 44 00:03:04,920 --> 00:03:05,920 Exactly. 45 00:03:05,920 --> 00:03:10,760 So what they typically will do if I only have my two wires going to the outdoor unit, that 46 00:03:10,760 --> 00:03:15,660 is my DC communicating number one and number two. 47 00:03:15,660 --> 00:03:20,120 And so if it was like a two stage unit, they simply have you put the factory transformer 48 00:03:20,120 --> 00:03:24,920 or it's already supplied with a factory transformer on the outdoor unit. 49 00:03:24,920 --> 00:03:30,020 And so we do not want to connect the R and C from the outdoor unit to the indoor unit 50 00:03:30,020 --> 00:03:34,600 if I have a transformer out there, because then our AC voltages would be doing what? 51 00:03:34,600 --> 00:03:35,920 They'll be fighting each other. 52 00:03:35,920 --> 00:03:37,720 They'll be out of phase. 53 00:03:37,720 --> 00:03:38,820 Exactly. 54 00:03:38,820 --> 00:03:44,320 So what we do is if we have a transformer outdoor, that is supplying power to the outdoor 55 00:03:44,320 --> 00:03:45,320 unit. 56 00:03:45,320 --> 00:03:47,880 So we do not need AC voltage outside. 57 00:03:47,880 --> 00:03:51,780 And if it's an inverter, it's doing that in the control board itself. 58 00:03:51,780 --> 00:03:58,000 So the power supply of the board, the inverter board is managing the entire outdoor unit. 59 00:03:58,000 --> 00:04:01,320 So all it needs to do is communicate what are we doing? 60 00:04:01,320 --> 00:04:02,320 Are we running in heating? 61 00:04:02,320 --> 00:04:03,980 Are we running in cooling? 62 00:04:03,980 --> 00:04:05,680 And so how does it do that? 63 00:04:05,680 --> 00:04:12,040 Well, it's actually a very common process, not just in our industry, but in many communicating 64 00:04:12,040 --> 00:04:13,200 networks. 65 00:04:13,200 --> 00:04:18,040 So it's part of the RS-485 communicating system that's been around for decades. 66 00:04:18,040 --> 00:04:19,640 We use it for telephones. 67 00:04:19,640 --> 00:04:21,860 We use it for computer communications. 68 00:04:21,860 --> 00:04:24,040 We use it for a lot of things. 69 00:04:24,040 --> 00:04:33,480 And so what we do is we create a positive and a negative pathway in reference to ground. 70 00:04:33,480 --> 00:04:36,920 And this is where a lot of technicians, this is where a lot of people get caught up when 71 00:04:36,920 --> 00:04:41,120 we're thinking about the sequence of operation of a communicating system. 72 00:04:41,120 --> 00:04:49,920 If I have a positive and I have a negative, but it's in reference to ground, well, what 73 00:04:49,920 --> 00:04:54,160 do I normally do with the common side of an AC transformer tie? 74 00:04:54,160 --> 00:04:58,480 Well, half of the industry grounds that and the other half does not. 75 00:04:58,480 --> 00:04:59,440 Exactly. 76 00:04:59,440 --> 00:05:03,720 So with this particular system, you're going to find all of these transformers are going 77 00:05:03,720 --> 00:05:09,020 to be grounded so that common is a reference to ground. 78 00:05:09,020 --> 00:05:16,960 And so with that DC voltage, what we actually do is we separate out the signals in reference 79 00:05:16,960 --> 00:05:18,540 to ground. 80 00:05:18,540 --> 00:05:25,140 So we reduce the voltage down to five volts and then we put it in reference to ground. 81 00:05:25,140 --> 00:05:35,000 And so by using diodes and by using resistors, we can actually create a five volt DC pathway. 82 00:05:35,000 --> 00:05:37,200 So that's the bandwidth. 83 00:05:37,200 --> 00:05:44,280 And because we are now putting it into reference to ground, we can shift that ground from center 84 00:05:44,280 --> 00:05:46,360 just a little bit. 85 00:05:46,360 --> 00:05:51,120 And so that we have more voltage going to the positive side than what we have going 86 00:05:51,120 --> 00:05:54,400 to the negative side of our bandwidth. 87 00:05:54,400 --> 00:06:01,440 And so as technicians, it's a little bit different to think about this DC voltage. 88 00:06:01,440 --> 00:06:05,400 But when we think about it in reference to ground, it starts simplifying it. 89 00:06:05,400 --> 00:06:11,260 So with that DC, remember, most of our power supply is starting at that indoor unit. 90 00:06:11,260 --> 00:06:15,800 If I disconnect the wires at the indoor unit, whether it's a gas furnace or an air handler, 91 00:06:15,800 --> 00:06:24,800 when I put my meter on volts DC, I can now look for my five volts, but because it is 92 00:06:24,800 --> 00:06:30,560 in reference to ground and we have a negative voltage and we have a positive voltage, it's 93 00:06:30,560 --> 00:06:35,580 a little bit different of a thought process. 94 00:06:35,580 --> 00:06:42,600 So Ty, if I was thinking five volts DC, what would my brain immediately think of to look 95 00:06:42,600 --> 00:06:47,200 for between the positive terminal and the negative terminal? 96 00:06:47,200 --> 00:06:49,920 Oh, you would think five volts. 97 00:06:49,920 --> 00:06:52,680 Yeah, you would. 98 00:06:52,680 --> 00:06:54,200 That doesn't actually happen. 99 00:06:54,200 --> 00:06:56,700 And here's why. 100 00:06:56,700 --> 00:07:01,760 When we add the reference to ground into that DC circuit, we put that reference to ground, 101 00:07:01,760 --> 00:07:04,980 remember, I said just below its neutral point. 102 00:07:04,980 --> 00:07:11,500 And so we actually have to find ground to be able to check these DC voltages. 103 00:07:11,500 --> 00:07:14,000 And so what did we do with our transformer? 104 00:07:14,000 --> 00:07:15,320 We grounded one side. 105 00:07:15,320 --> 00:07:17,640 Yes, to common. 106 00:07:17,640 --> 00:07:26,920 So on the DC communicating Daikin platform, we simply put our meter on the volts DC. 107 00:07:26,920 --> 00:07:37,880 We use ground or common as our reference point, and we can go from ground to number one, and 108 00:07:37,880 --> 00:07:41,480 we're going to see our DC voltage. 109 00:07:41,480 --> 00:07:45,440 And it's actually going to typically will be around 2.8 volts DC on the gas furnace. 110 00:07:45,440 --> 00:07:48,800 Air handler is a little bit different, but on the gas furnace, we're going to see about 111 00:07:48,800 --> 00:07:56,360 a 2.8 volts DC from common or ground to that positive terminal. 112 00:07:56,360 --> 00:08:02,820 And then if we keep our one terminal on ground and we go to that number two, we actually 113 00:08:02,820 --> 00:08:10,800 read a negative DC voltage because it is below ground. 114 00:08:10,800 --> 00:08:11,800 Kind of makes sense? 115 00:08:11,800 --> 00:08:13,600 It does make sense. 116 00:08:13,600 --> 00:08:18,180 And between the two, we actually have five volts DC. 117 00:08:18,180 --> 00:08:23,240 But because one of them is going above ground 2.8 volts and one of them is going below ground 118 00:08:23,240 --> 00:08:30,360 2.2 volts, it actually calculates out to five volt DC. 119 00:08:30,360 --> 00:08:38,800 So if I was to take my meter, Ty, and I went between number one and number two, and I was 120 00:08:38,800 --> 00:08:45,320 expecting to read five volts DC, but I didn't read five volts DC, what do you think we might 121 00:08:45,320 --> 00:08:47,680 see between number one and number two? 122 00:08:47,680 --> 00:08:50,200 Oh, you got me, Cliff. 123 00:08:50,200 --> 00:08:51,200 I don't know. 124 00:08:51,200 --> 00:08:52,200 I know. 125 00:08:52,200 --> 00:08:53,680 This got me stuck from the beginning. 126 00:08:53,680 --> 00:08:54,880 So think about that. 127 00:08:54,880 --> 00:08:57,680 As we're driving down the road, we're doing a sequence of operation, we're preparing to 128 00:08:57,680 --> 00:09:03,840 go to this Daikin communicating system, and we want to check our communicating voltages. 129 00:09:03,840 --> 00:09:07,780 If we were thinking about it as a five volt DC system, and I was expecting to see five 130 00:09:07,780 --> 00:09:11,460 volts DC and I didn't, I might think that there was a problem. 131 00:09:11,460 --> 00:09:21,700 But because we went above the ground reference 2.8 volts for one point, and we went below 132 00:09:21,700 --> 00:09:28,500 the ground 2.2, a negative 2.2 volts DC, on the other point, when we measure from those 133 00:09:28,500 --> 00:09:32,820 two points, we actually add them together. 134 00:09:32,820 --> 00:09:40,360 A positive 2.8 minus the 2.2, that negative 2.2. 135 00:09:40,360 --> 00:09:47,580 So what we end up with on the number one to number two terminal should be approximately 136 00:09:47,580 --> 00:09:50,120 0.6 volts DC. 137 00:09:50,120 --> 00:09:52,840 Right, that makes sense. 138 00:09:52,840 --> 00:09:53,840 Yeah. 139 00:09:53,840 --> 00:09:56,200 So we have to change our thought process. 140 00:09:56,200 --> 00:10:00,040 AC, we always think about AC as being positive. 141 00:10:00,040 --> 00:10:06,640 Even though it's really, when we look at the sine wave, it's got a positive and negative 142 00:10:06,640 --> 00:10:07,640 reference. 143 00:10:07,640 --> 00:10:09,960 We're typically looking for an RMS voltages in that. 144 00:10:09,960 --> 00:10:16,160 But in DC, we truly can have voltages above the ground reference and voltages below the 145 00:10:16,160 --> 00:10:17,800 ground reference. 146 00:10:17,800 --> 00:10:24,120 So on that DICAN communicating system, when I go between number one and number two, I'm 147 00:10:24,120 --> 00:10:29,600 actually looking for 0.6 volts DC or greater. 148 00:10:29,600 --> 00:10:36,720 And the reason being is that 0.6 volts DC is our bandwidth for our signals to communicate 149 00:10:36,720 --> 00:10:38,120 on. 150 00:10:38,120 --> 00:10:44,840 And if I have less than 0.6 volts DC, that means that my positive and my negative signals 151 00:10:44,840 --> 00:10:48,160 have been affected by something. 152 00:10:48,160 --> 00:10:50,440 I've got a break in the wire. 153 00:10:50,440 --> 00:10:52,800 I've got a bad connection. 154 00:10:52,800 --> 00:10:58,760 I've got a control wire that I reuse that was chewed up by a mouse and got corroded 155 00:10:58,760 --> 00:11:04,040 and worked fine on 24 volts AC but doesn't like 5 volts DC. 156 00:11:04,040 --> 00:11:08,440 It's actually some of the most common things that we see for the communication. 157 00:11:08,440 --> 00:11:13,240 So what we do when we're troubleshooting a DC communicating system on these, particularly 158 00:11:13,240 --> 00:11:16,840 the DICAN, is we disconnect everything. 159 00:11:16,840 --> 00:11:18,480 We start at our indoor unit. 160 00:11:18,480 --> 00:11:23,920 And if it is the gas furnace, we're going to see a 2.8 and a minus 2.2 from ground to 161 00:11:23,920 --> 00:11:25,660 number one, ground to number two. 162 00:11:25,660 --> 00:11:33,040 If it's an air handler, it'll sometimes be less and be like 1.9 and 1.3. 163 00:11:33,040 --> 00:11:36,320 They use more of a 3 volt DC versus that 5 volt. 164 00:11:36,320 --> 00:11:44,880 But the most important part is that we have a 0.6 volt bias or greater between number 165 00:11:44,880 --> 00:11:47,480 one and number two. 166 00:11:47,480 --> 00:11:51,520 If I don't, I've got a problem. 167 00:11:51,520 --> 00:11:54,800 Now Ty, let's think about this. 168 00:11:54,800 --> 00:12:07,320 If I don't have my proper voltages in reference to common, is there any place that I could 169 00:12:07,320 --> 00:12:16,040 possibly look to find a problem with why I don't have a good common reference? 170 00:12:16,040 --> 00:12:19,880 I would start looking at the connections first. 171 00:12:19,880 --> 00:12:22,480 In particularly the connections to ground. 172 00:12:22,480 --> 00:12:23,660 Yes. 173 00:12:23,660 --> 00:12:27,080 So here's one of the things that we see out in the field, especially here in the Midwest, 174 00:12:27,080 --> 00:12:32,400 where we have old wiring and a lot of furnaces were only wired with a hot and a neutral and 175 00:12:32,400 --> 00:12:33,760 didn't have a proper ground. 176 00:12:33,760 --> 00:12:36,840 I mean, we'd see that and go, oh my gosh, does that really happen? 177 00:12:36,840 --> 00:12:38,620 Yes, it absolutely happens. 178 00:12:38,620 --> 00:12:45,740 And so what we have is we have the potential for a bad ground to that indoor unit to throw 179 00:12:45,740 --> 00:12:47,760 off those DC voltages. 180 00:12:47,760 --> 00:12:52,840 And so unfortunately, a lot of technicians, if they were learning how to check the voltages 181 00:12:52,840 --> 00:12:58,360 and they measured and they found that they had no voltage or very, very low voltage, 182 00:12:58,360 --> 00:13:02,120 they would immediately go to the indoor board to replace it. 183 00:13:02,120 --> 00:13:07,680 In actuality, we need to verify the ground to the indoor unit. 184 00:13:07,680 --> 00:13:12,960 And Ty, what are some good ways we can check ground coming into the power supply of our 185 00:13:12,960 --> 00:13:14,760 indoor unit? 186 00:13:14,760 --> 00:13:17,120 The ground lug, the ground terminal? 187 00:13:17,120 --> 00:13:18,240 Absolutely. 188 00:13:18,240 --> 00:13:25,180 So what we end up finding a lot of times on that ground is if it has a bad connection, 189 00:13:25,180 --> 00:13:27,200 we can lose that potential. 190 00:13:27,200 --> 00:13:33,200 So what I always like to do is to be able to check the voltages from ground to our hot, 191 00:13:33,200 --> 00:13:37,200 make sure that we have, if it's a 120 volt system, we've got 120 volt from ground to 192 00:13:37,200 --> 00:13:41,140 hot and we have the exact same voltage from neutral to hot. 193 00:13:41,140 --> 00:13:45,820 And if there's any difference in those voltages, we know that we've had some kind of a bad 194 00:13:45,820 --> 00:13:51,600 connection on that ground lug or a poor connection of ground somewhere or no ground. 195 00:13:51,600 --> 00:13:56,640 And so if there's a difference in those voltages from ground to hot and neutral to hot, we 196 00:13:56,640 --> 00:14:01,200 know that we have either on that neutral or that ground, we have some kind of a failure, 197 00:14:01,200 --> 00:14:03,280 some kind of an interruption. 198 00:14:03,280 --> 00:14:09,060 So if we verify that we have good ground, we've started our indoor board and we have 199 00:14:09,060 --> 00:14:15,800 0.6 volts or greater, we know that we have started with a good DC voltage. 200 00:14:15,800 --> 00:14:19,520 And now we would connect the indoor communicating thermostat. 201 00:14:19,520 --> 00:14:21,280 So we connect those four wires. 202 00:14:21,280 --> 00:14:29,840 And so from common to R, I got to put my meter on, how about volts AC? 203 00:14:29,840 --> 00:14:32,240 Make sure that I got my 24 volts AC. 204 00:14:32,240 --> 00:14:40,160 But then from common to one and common to two, that's where I would have my DC voltages. 205 00:14:40,160 --> 00:14:45,040 And so I connect the indoor thermostat and I check my voltages between number one and 206 00:14:45,040 --> 00:14:47,800 number two at the thermostat. 207 00:14:47,800 --> 00:14:51,960 And it should be the same as what I had started with my indoor unit because that thermostat 208 00:14:51,960 --> 00:14:53,480 doesn't have much of a load on it. 209 00:14:53,480 --> 00:14:55,880 It's just communicating. 210 00:14:55,880 --> 00:15:06,960 Now if I connect my outdoor unit and my voltages, my DC voltages get janky, now I've actually 211 00:15:06,960 --> 00:15:10,680 determined a place to look for my problems. 212 00:15:10,680 --> 00:15:17,600 And here's where the most common failure on a communicating system on the outdoor unit 213 00:15:17,600 --> 00:15:19,020 comes from. 214 00:15:19,020 --> 00:15:24,880 So Ty, as a technician, and we were working on a AC powered outdoor unit. 215 00:15:24,880 --> 00:15:30,480 So whether a single stage, two stage, whatever it was, if it was just a plain Jane, I got 216 00:15:30,480 --> 00:15:36,680 a compressor, a contactor, and a motor and a capacitor. 217 00:15:36,680 --> 00:15:39,080 Did it really care about ground? 218 00:15:39,080 --> 00:15:41,320 Nope, not at all. 219 00:15:41,320 --> 00:15:45,720 Because it would still run on common and hot. 220 00:15:45,720 --> 00:15:53,760 It only used ground as a reference point if it had a failure and it had current being 221 00:15:53,760 --> 00:15:57,120 able to make its way back to the panel through the ground circuit. 222 00:15:57,120 --> 00:16:02,560 So with our traditional legacy systems, ground was not really important for the outdoor unit 223 00:16:02,560 --> 00:16:04,280 except for safety. 224 00:16:04,280 --> 00:16:05,800 Okay? 225 00:16:05,800 --> 00:16:08,760 So let's think about this. 226 00:16:08,760 --> 00:16:14,680 Because my communicating system relies on the reference to ground and because my new 227 00:16:14,680 --> 00:16:25,360 unit has power from its own power supply outside, where does it get common or the ground reference 228 00:16:25,360 --> 00:16:28,920 for number one and number two? 229 00:16:28,920 --> 00:16:35,640 This is where I sit in class and go, do, do, do, do, do, do, do. 230 00:16:35,640 --> 00:16:43,560 Where my mind is running is if the grounding rod outside is corroded, which often happens, 231 00:16:43,560 --> 00:16:47,080 then that could also lead to an issue with your communication system because it's not 232 00:16:47,080 --> 00:16:49,240 having a reference to ground. 233 00:16:49,240 --> 00:16:50,720 Bingo. 234 00:16:50,720 --> 00:16:56,800 The most common misdiagnosed portion of a failed communicating system when it's referenced 235 00:16:56,800 --> 00:17:02,360 to the outdoor unit is the ground connection back to the electrical panel or through the 236 00:17:02,360 --> 00:17:05,120 grounded of the circuit. 237 00:17:05,120 --> 00:17:12,440 Because when it was engineered, they assumed that all electrical systems were properly 238 00:17:12,440 --> 00:17:15,760 grounded, including the outdoor unit. 239 00:17:15,760 --> 00:17:21,520 And so when that 24 volt common and 24 volt hot was removed from the circuit going to 240 00:17:21,520 --> 00:17:27,960 the outdoor unit and it only had number one and number two, those DC voltages that were 241 00:17:27,960 --> 00:17:36,400 referencing or signaling to ground, the assumption was that they would get that path from ground 242 00:17:36,400 --> 00:17:38,440 of the outdoor unit. 243 00:17:38,440 --> 00:17:45,360 And so what often gets overlooked is the ground from the outdoor unit to the disconnect, to 244 00:17:45,360 --> 00:17:50,780 the ground rod, or to the back to the ground of the indoor panel, the electrical panel. 245 00:17:50,780 --> 00:17:55,400 And so how we find that is we do that same DC voltage check. 246 00:17:55,400 --> 00:18:01,400 So we check from common to number one and then common to number two to look for that 247 00:18:01,400 --> 00:18:05,000 0.6 volt DC difference at the indoor unit and at the thermostat. 248 00:18:05,000 --> 00:18:13,160 When we go to the outdoor unit, since we don't have common, we now use ground because it 249 00:18:13,160 --> 00:18:14,160 is our common. 250 00:18:14,160 --> 00:18:19,440 And if we don't have those same signals and it's an immediate indicator that we have a 251 00:18:19,440 --> 00:18:27,040 poor ground between the outdoor unit and the disconnect and the electrical panel. 252 00:18:27,040 --> 00:18:31,200 And a lot of technicians don't realize what that is. 253 00:18:31,200 --> 00:18:36,160 They assume that those two wires that are going to the outdoor unit, all of the communication 254 00:18:36,160 --> 00:18:38,800 is happening on those two wires alone. 255 00:18:38,800 --> 00:18:45,120 And that is somewhat true, but the circuit relies on ground for the reference point for 256 00:18:45,120 --> 00:18:46,720 those DC voltages. 257 00:18:46,720 --> 00:18:52,280 And if we have a bad ground, if we have a corroded lug, if we have a ground wire that 258 00:18:52,280 --> 00:18:58,720 is rotten, is not making good connection, if we have what I've also seen in some of 259 00:18:58,720 --> 00:19:04,240 the older disconnects, they used aluminum lug screws for the ground wire. 260 00:19:04,240 --> 00:19:09,280 And those aluminum lug screws when connected to copper oxidize and corrode really bad and 261 00:19:09,280 --> 00:19:12,080 they actually lose their conductivity. 262 00:19:12,080 --> 00:19:18,280 So I've had troubleshooting calls that were non-communicating outdoor units that the fix 263 00:19:18,280 --> 00:19:24,440 was as simple as loosening the screws, cleaning off the corrosion, putting some dielectric 264 00:19:24,440 --> 00:19:30,880 grease and cranking them back down to restore our communication to ground and our communicating 265 00:19:30,880 --> 00:19:32,960 systems start talking. 266 00:19:32,960 --> 00:19:33,960 That's interesting. 267 00:19:33,960 --> 00:19:35,420 Isn't that crazy? 268 00:19:35,420 --> 00:19:41,640 So when we start thinking about DC communicating systems, our sequence of operation is we begin 269 00:19:41,640 --> 00:19:43,500 at the indoor unit. 270 00:19:43,500 --> 00:19:50,680 We verify our voltages from ground or common to number one and to number two. 271 00:19:50,680 --> 00:19:55,240 We check the DC voltages between number one and number two to make sure we have 0.6 volts 272 00:19:55,240 --> 00:19:58,360 DC bias or greater. 273 00:19:58,360 --> 00:20:03,320 We check our indoor unit, we add the thermostat to the indoor unit, we check our thermostat. 274 00:20:03,320 --> 00:20:08,880 And then when those are the same, we add the outdoor unit and make sure that nothing changed. 275 00:20:08,880 --> 00:20:14,920 In the instance that we have an extremely long control wire from the indoor unit to 276 00:20:14,920 --> 00:20:19,760 the outdoor unit or we have poor conductors, it's actually going to show itself. 277 00:20:19,760 --> 00:20:24,320 And in some cases, we have to increase that bias voltage. 278 00:20:24,320 --> 00:20:30,140 And on those DICON units, they actually have a switch on the outdoor unit that boost that 279 00:20:30,140 --> 00:20:31,520 bias voltage. 280 00:20:31,520 --> 00:20:34,420 It opens up that bandwidth a little bit. 281 00:20:34,420 --> 00:20:40,760 And so on some systems, when our bias is lower than 0.6 volts DC, we have to engage that 282 00:20:40,760 --> 00:20:45,760 to be able to make sure that we have above 0.6 volts DC. 283 00:20:45,760 --> 00:20:51,720 Because that 0.6 volts DC might be good right now, but because it's in reference to ground, 284 00:20:51,720 --> 00:20:56,840 it could change the next time that it rains or the next time that it gets really dry and 285 00:20:56,840 --> 00:20:59,360 arid outside and affects ground. 286 00:20:59,360 --> 00:21:02,760 And that 0.6 volt DC bias can drop. 287 00:21:02,760 --> 00:21:12,200 So moral of the story, on a DICON in particularly, 5 volt DC communicating system, we must check 288 00:21:12,200 --> 00:21:18,160 from common to one, common to two, and the difference between one and two shall be 0.6 289 00:21:18,160 --> 00:21:21,840 volts DC or greater, or you're coming back. 290 00:21:21,840 --> 00:21:22,840 That's interesting. 291 00:21:22,840 --> 00:21:24,800 I did not know that. 292 00:21:24,800 --> 00:21:26,760 I love that. 293 00:21:26,760 --> 00:21:30,760 All right, Ty, thanks for joining us and we appreciate having a conversation on DC voltages 294 00:21:30,760 --> 00:21:33,520 and we'll catch you next time on Did You Know? 295 00:21:33,520 --> 00:21:42,540 The Esco HVAC Podcast.