In this instructional video Derek Cole explains the inner workings of a basic furnace‑only air‑conditioning system, which lacks a heat‑pump function and therefore has a minimal component set: a contactor, a run capacitor, and an optional compressor‑saver (start‑assist). He describes how the contactor switches low‑voltage thermostat signals to high‑voltage power for the compressor and fan, and how visual signs such as burn marks indicate impending failure. Cole then details the run capacitor’s dual ratings (compressor side 4‑5 µF, fan side 5 µF), how to measure its actual capacitance, and the tolerance limits (±5‑6 %) that determine if it needs replacement. He introduces the compressor‑saver, explaining its role in reducing startup current and extending compressor life. The core of the maintenance routine involves measuring startup and running amperage of the compressor and fan, comparing these values to the data‑plate specifications (e.g., max startup 68 A, max running 14 A for the compressor; 0.8 A for the fan). He demonstrates a case where the compressor’s startup draw is excessively high (73 A vs 63 A spec) despite a normal running draw, indicating imminent failure. Finally, he notes the importance of checking valve covers for oil, as oil presence signals a refrigerant leak, which should never occur in a properly sealed system. The video concludes with the recommendation to present these findings to the customer after confirming proper indoor temperature split.
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So inside here, components-wise, because this is just a furnace AC setup system, the system does not have the heat pump ability where the condenser can produce heat and cool. So in this case, there's not a control board to do much of switching from, you know, cooling to heating cycles. So this is just straight cooling. So this has very minimal components. So this would be the contactor, this would be the capacitor, and this would be the compressor saver, or it's an add-on. The contactor operates both low and high voltage. The low voltage, when thermostat tells it that I need you to operate,, it closes the coil, which creates a magnetic field and pulls in the contact. And once it closes, it allows the high voltage to pass through, go to the compressor and the fan to operate the compressor. And the capacitor, what this does— this is a run capacitor. It has two purposes. It assists the compressor and the fan in starting and maintaining the speed. Now, part of our routine checkup when we do maintenance on the system, we check to see the condition of the contactor. Like in this case, this contactor has a lot of burn marks on it, so it's considered pitted. So at some point, you'll find that when it tries to energize, it won't make contact. So like at this point, this contactor is at the point of it will fail at some given point. We check the capacitor to find the ratings that are on it. As you can see on this particular one, It is a 4-5+5. That means the 4-5 operates the compressor side of it and the 5 operates the fan side of it. Now it's rated in MFD, so we have meters that we can check to see the ratings on it in comparing to what it's supposed to be, and we determine if the capacitor is failed. Now it only gives you a 6% stress point in this case is a 5%. Some is 6%. So anything below a 5% of the 4 to 5 or the 5, this capacitor is considered fail and needed to be replaced. Because what's going to happen at that point, the compressor or the fan will be doing more than what it's supposed to, because this, this is what assisted in running and maintain the speed. So either the compressor or the fan will be running not as fast as supposed to, but it'll be struggling. And in that case, it's pulling more amp draw, so you're spending more utility. And basically, it's a— most unit, older unit does not come with a start assist, which is called a compressor saver. So we traditionally add these to the capacitor when we find the compressor is drawing a higher amp draw. What this does, it helps the compressor in the startup cycle, um, to make sure it starts and use, you know, it extend the life of the compressor. So at this point, I'm going to check the capacitor to see the condition and the ratings on it right now. So this is rated 4 to 5, and I'm getting 4 to 4. So that's telling me that the capacitor on the compressor side is still good. On the fan side, it's rated 5, and I'm getting 4.5, so it's still within that 5% range. So this capacitor is considered okay. Another part of our check is we check to make sure we have our valve covers on, and we look for any evidence of oil leaks anywhere. Whenever we see oil present, it usually indicates possible leaking. Which should prompt us to go a little further to make sure there's not a leak on the system. System typically should never have a leak. Once system is charged and in operation, it should never lose refrigerant. So if you ever lose refrigerant, you have a problem. That means there is a leak somewhere on the system. Now as far as operation, we typically take the startup amp draw for the compressor and the run amp draw. And as far as the condenser fan, we check the running amp of it. And you usually find on the data plate, it gives you basic information of what we're looking for. In the case of the compressor, the maximum running amp should have been 14, maximum startup amp should have been 68. As far as the motor, it should be— let me see if I can find it here— fan motor is a 1.8 horsepower, maximum amp draw supposed to be 0.8. So we rate whatever we find compared to the data plate, which tells us the condition of the compressor and the fan. So the fan, it was 0.8, so it's telling us our fan is perfectly fine. It's doing what it's supposed to. From the data plate, it was 0.8, and we're getting 0.8. Now check the compressor. So my compressor startup was 73, which on the data plate I think it was 63 maximum. So my compressor startup amp on this is extremely high. So even though it has a compressor saver, that's telling me the compressor at some point will fail because even with a compressor saver, the amp draw is extremely high. Now once it starts, the running is fine. The maximum was 14 and I'm getting 6.9. So, oh no, running amp is perfectly okay. The perfect operation on the inside to verify that we are getting good temperature split on the inside, and then present my finest to the customer.
