General Atomics UAV cooling solution

A fully operational environmental control unit (ECU) in a satellite hub is the difference between reliable connections for millions of customers, or costly downtime for both the users and the company. On a remote desert airstrip, it’s the difference between functioning surveillance reconnaissance systems, or the inability to complete a critical intelligence gathering mission.

And if an ECU isn’t operating at 100% capacity, facility managers can’t afford to be caught flat-footed.

Fortunately, there is a straightforward hierarchy to follow for evaluating mission critical ECUs. By working through these stages, facility managers and on-site technicians can gain important insight into the state of electrical, refrigeration and mechanical components and take the necessary steps towards returning ECUs to full capacity.

These troubleshooting and evaluation practices, along with insights from your product manual, will ensure minimal downtime, improved service life and a swift return to service for the mission critical ECU.

Stage 1: Initial evaluation for on-site technicians

If you’re noticing problems with your ECU, such as the unit running but not cooling or an evaporator that has iced over, a visual inspection is the first stage.

Preliminary evaluation

Check the power source to see if it has been interrupted or a breaker has tripped. It’s also important to check the air filters right away, as dirty or blocked filters are a common problem that can cause obstruction to proper air circulation.

Remediate these items (connect the power, clean or replace filters) and move on to the next step if the problem persists.

Visual inspection of refrigeration and mechanical equipment


On-site technicians should conduct a commonsense evaluation of the equipment and review the physical state of all components.

On the refrigeration side, check for visual damage, corrosion or buildup of debris. These can lead to loss of efficiency, leakage of refrigerant or malfunction. For example, if diagnostics reveals that the expansion valve is stuck in an open position, that can cause the suction pressure to be too high and will require a new valve and sensing bulb.

Damage or build up doesn’t require special tooling or knowledge to recognize and will be easy to identify on these components:

  • Coils
  • Heat exchanger
  • Condenser and evaporator coil
  • Refrigerant lines
  • Evaporator blower
  • Condenser blower
  • Switches
  • Sensors
  • Condensate drain hose

Also review the refrigerant sight glass, which indicates moisture levels in the refrigerant. If there are constant bubbles, this indicates low refrigerant, while a yellow color indicates the presence of moisture.

Complete a similar visual assessment on mechanical components, looking for obvious buildup or damage on:

  • Control and service panels
  • Fans, which should also be checked for smooth rotation
  • Outside covers and panels, which should also be checked for missing hardware like fasteners

For any parts that are dirty, wipe them off with water. Replace any damaged components.

It’s required to complete a leak detection test if a refrigeration system component (i.e. compressor, valve, filter drier, etc.) is replaced. This can be done with three potential methods:

  • A visual inspection, where you look for the presence of oil around valve caps, seals or vibrating parts.
  • A bubble test, where you spray a solution of liquid detergent and water on brazed points suspected of leaking and look for the formation of bubbles.
  • An electronic leak detector, where you pass a probe along the refrigeration lines and all brazed points.

Visual and bubble tests are simple and inexpensive to perform. But an electronic leak detector is generally the preferred method because it’s the quickest way to find an unknown leak and is effective in finding micro leaks.

Visual inspection of electrical components

Only inspect electrical components while the system is powered off. Be sure to unplug the system and disconnect from the power source (i.e. flip the appropriate breaker switches to the “off” position) to guarantee safety for technicians.

Check all wiring and cables for loose or missing connections, chaffed or fraying wires or any exposed bare wires. Also look for visible evidence of equipment damage or wear to relays, which may be due to overheating or even end of life cycle. For any damaged components, replace them.

Additional inspection for ruggedized equipment

Facility managers working with ruggedized, portable and trailer-mounted units should also inspect the connections of mounting hardware. These units face difficult terrain, tough environmental conditions and moderate to significant duress and should be tightened to the correct torque. Otherwise, the unit is at risk of disconnecting during transportation.

If you have completed the above visual inspections and still haven’t discovered the source of the problem, the next step is to bring in an HVAC technician.

Stage 2: Testing criteria for HVAC technicians

An HVAC technician will be able to investigate further into the state of electrical, refrigeration and mechanical components and find the root cause of your ECU’s problem.

The following refrigeration and electrical tests should be conducted by an experienced HVAC professional. We’re outlining these procedures here not to encourage facility managers to conduct the tests themselves, but rather to share guiding information on what your technician should be testing for.

Note: For operations without an in-house HVAC technician, it’s important to bring in technicians with experience in self-contained HVAC systems (i.e. ECUs) as they differ from those in residential and commercial spaces.

Refrigeration test: Superheat and subcooling measurements


Proper refrigerant levels are crucial for any HVAC system to operate effectively and provide cooling in an efficient manner. Too much or too little refrigerant — i.e. overcharged or undercharged — can not only lead to improper cooling, but it can also damage the ECU.

To test refrigerant levels, the technician will conduct superheat measurements (refrigerant gas temperature above boiling point) and subcooling measurements (difference between the discharge saturation temperature and the discharge line temperature) using high- and low-pressure gauges.

Then, by using a pressure-temperature conversion chart specific to your system’s refrigerant, they will determine whether the system is overcharged or undercharged. For example, high subcooling can indicate an overcharged system. Once the reading is determined, they’ll mitigate the problem by adding or removing refrigerant or recommending service where needed.

Electrical tests

Hipot testing

The dielectric test, commonly known as the hipot test, verifies that the HVAC equipment can withstand a high voltage surge and is conducted with a dielectric tester. If the insulation can withstand a much higher voltage, then it will be able to function at normal levels for the life of the product.

A rule of thumb formula for test voltage is:

(Normal operation voltage x 2) + 1000 = Test voltage

This test is helpful in finding damaged insulation, stray wire strands, corrosive contaminants around conductors and tolerance errors in cables. If the unit doesn’t pass the hipot test, consult your HVAC manufacturer.

Insulation resistance test

This test provides a quantifiable value for the resistance of an HVAC system’s insulation. The technician will apply a voltage across the insulation and measure the corresponding leakage current to calculate the resistance.

Stable conditions (temperature, humidity) are important for accuracy with this test. While you want ohm readings to be near the values listed on the spec sheet, it’s more important for the ohm values to be similar across circuit readings. For example, a reading of 30 ohms, 31 ohms and 15 ohms across three circuits would indicate a connection problem or a non-functioning element. If the unit doesn’t pass the resistance test, consult your HVAC manufacturer.

Test of continuity

A continuity test verifies that currents flow easily from one point in the unit to another and helps identify bad wires or connections. Using an ohmmeter, a small current is sent through the circuit to determine if the appropriate amount of current is flowing. If the unit doesn’t pass the continuity test, consult your HVAC manufacturer.

Reliable HVAC systems for critical environments

Troubleshooting problems is inevitably a part of operating any mechanical system. But efficiently solving these refrigeration, electrical or mechanical problems at the source means a shorter window between when you first spot the issue and when you’ve returned your unit to 100% capacity.

As an experienced provider of ECUs for critical environments, Air Rover engineers know how to design and build systems with industry-leading durability, constantly working to minimize downtime for your mission critical operation. Start a conversation about high reliability ECUs today.