Final answer:
In a system with 200 psi on the high side and 0 psi on the low side, there could be a blockage or a malfunctioning compressor. Like tire gauges that read zero at atmospheric pressure, mechanical gauges for HVAC systems only report positive values above atmospheric pressure.
Step-by-step explanation:
When hooking up gauges to a system and you find that there are 200 psi on the high side and 0 psi on the low side, it can indicate a possible blockage or restriction on the low side, or it could mean that the compressor is not functioning properly. This situation is often seen in refrigeration or air conditioning systems, where improper pressure readings suggest there's an issue to be addressed. Considering the function of a tire gauge as an example where it reads zero at atmospheric pressure, most mechanical gauges, including HVAC gauges, are also designed to read zero at atmospheric pressure and only indicate positive values when the pressure is greater than atmospheric. Therefore, a reading of zero on the low side signifies that there is no pressure above atmospheric pressure in that part of the system, which is not normal during operation.