What the Type 3 exam covers
Type 3 (Type III in older material) certification covers low pressure appliances: equipment whose refrigerant boils above 10 degrees C (50 F) at atmospheric pressure, so the system runs at or below atmospheric pressure. The dominant equipment is the large centrifugal chiller in commercial buildings, hospitals, and universities. The active refrigerant is R-123; R-11 is fully phased out. The section is 25 questions, pass mark 72% (18 of 25).
Most technicians search for it as the EPA Type 3 practice test; the EPA 608 Type 3 study guide explains the reasoning behind each answer.
Why a low pressure chiller runs in a vacuum. R-123 boils at 82 degrees F, so a chilled water evaporator sits well below atmospheric pressure; an idle machine reads 1.2 inches Hg vacuum at 80 degrees F. Because a low pressure system operates below atmospheric pressure, leaks draw air and moisture in rather than pushing refrigerant out, which is why low pressure appliances require a purge unit. Raise the machinery room above 82 degrees F and an R-123 shell goes positive; the leak direction reverses.
Machinery room sensors, alarms, and R-123 exposure
R-123 sits in ASHRAE Standard 34 safety group B1, higher toxicity with no flame propagation, with an exposure limit of 50 ppm, so chiller machinery rooms need refrigerant monitors and self contained breathing apparatus on site. ASHRAE Standard 15 requires room sensors and alarms to detect refrigerant leaks from every safety group, not only B1, because refrigerant vapor is heavier than air and displaces oxygen at floor level. R-1233zd, the HFO alternative, is rated A1 but still runs below atmospheric pressure, so the same vacuum rules apply.
Taking the Type 3 exam: Core first, closed book, proctored
Every candidate sits the 25-question Core section first; the EPA 608 Core practice test covers it. The exam is closed book and proctored, in person or online; the EPA 608 certification online guide compares the online providers, and the EPA 608 certification cost page lists fees by organization. Core plus all three types is Universal (EPA 608 Universal practice test). Appliances with 5 pounds or less belong to the EPA 608 Type 1 practice test; high pressure equipment on R-22 or R-410A to the EPA 608 Type 2 practice test.
Low pressure system safety and equipment
Five numbers recur on the Type 3 exam:
| Parameter | Value | Why it matters on the exam |
|---|---|---|
| Rupture disc burst rating | 15 psig | Disc protects system from over pressure; know the value cold |
| Maximum nitrogen leak test pressure | 10 psig | Exceeding 10 psig blows the rupture disc; tested directly |
| Oil preheat temperature | 130 degrees F minimum | Required before startup to prevent bearing damage from slugging |
| Disposal recovery vacuum | 25 mm Hg absolute | EPA mandate for equipment with low pressure refrigerant; not inches Hg |
| Record retention (50 or more lb systems) | 3 years | Leak inspection, initial verification, follow up verification |
Rupture disc rated at 15 psig, working pressure capped at 10 psig
A low pressure chiller carries a rupture disc on the shell: a one time device that bursts at 15 psig and releases the charge to protect the vessel. Everything that raises pressure inside the machine is therefore held to 10 psig: nitrogen for leak testing, warm water on a charged machine, and the high pressure cut-out on a recovery unit. Relief valves are never installed in series; parallel, or through a three way valve, so one is always active.
Where low pressure chillers leak: open drive shaft seals, gaskets, and water boxes
On a low pressure refrigeration system with an open drive compressor, the motor sits outside the refrigerant shell and the shaft passes through a rotating seal. That shaft seal is the component particularly susceptible to leaks, and a compressor idle for months can harden the rubber in it and leak on startup. Gaskets, flanged joints, and charging connections come next. Water enters most often through a leaking tube or a failed condenser gasket; technicians open the water boxes, the removable end covers on the condenser and evaporator shells, to find and plug leaking tubes.
Chiller recovery, charging, and leak testing
Chiller recovery pulls the machine to 25 mm Hg absolute, charging runs the sequence in reverse, and leak testing a charged machine stays under 10 psig.
Recovery level: 25 mm Hg absolute before a major repair or disposal
Under 40 CFR §82.156, a low pressure appliance opened for a major repair or evacuated for disposal must be pulled to 25 mm Hg absolute. The target is the same whether the recovery equipment was made before or after November 15, 1993; equipment built after that date must have low loss fittings. Older prep material listing 25 in. Hg for pre-1993 machines is outdated. A repair that is not major needs only 0 psig before opening. After reaching the target vacuum, wait: if pressure rises above 2.5 mm Hg during the vacuum test, leak check again before charging.
Recovery sequence: liquid first, vapor second, water pumps running. Keep the system water pumps, recovery compressor, and recovery condenser water running, or water in the tubes freezes and ice splits them; if tube leaks are suspected, drain the water sides first. Remove liquid first, then vapor. Replacing a compressor, condenser, or evaporator is a major repair under 40 CFR §82.152; a burnout calls for an oil sample. Charging runs in reverse: refrigerant is added to a centrifugal machine through the evaporator charging valve, vapor first until saturation temperature passes 32 degrees F, then liquid; oil is preheated to 130 degrees F before startup.
Leak testing a charged low pressure chiller: warm water or heating blankets, never above 10 psig
A charged low pressure machine sits in a vacuum, so leak testing starts by raising its pressure. The most efficient method of leak checking a charged low pressure refrigeration unit is adding heat with circulated hot water or heating blankets; nitrogen is the pressurizing gas on an empty machine. Either way the pressure must not exceed 10 psig, because the rupture disc lets go at 15 psig. Then an electronic detector finds the leak, probing first at the drain valve opening, the lowest port. Suspected tube leaks are checked with a hydrostatic tube test kit: colored water under pressure, and dye seeping from a tube marks the leak.
Leak rate thresholds: 10% for a comfort cooling chiller, 30 days to repair
Most low pressure appliances are comfort cooling, so a chiller holding 50 or more pounds of refrigerant falls under the 10% annual leak rate threshold in 40 CFR §82.157; commercial refrigeration is 20% and industrial process refrigeration 30%. R-123 is an HCFC, so the rules apply. Past the threshold: 30 days to repair, an initial verification test before refrigerant goes back in, a follow up verification test within 30 days of normal operation. A failed test means redoing the repair or a retrofit or retirement plan within one year (18 months with a refrigerant exempt from the venting prohibition). Records are kept three years.
Purge units, air, and moisture in low pressure systems
What the purge unit does with non-condensables. Purge units are found only on low pressure chillers. Air and moisture infiltrate through shaft seals, gaskets, and fittings; air and other non-condensables collect at the top of the condenser, where the purge unit takes its suction, separates them from refrigerant vapor, vents the air, and returns the refrigerant to the evaporator. Left in the machine, air raises head pressure and cuts capacity, so high head pressure on a low pressure chiller points to air in the system.
Excessive purge running means a leaking system
Excessive running of a purge system on a low pressure chiller generally indicates a leaking system: the more air comes in, the more the purge runs, so logged purge runtime is the first leak alarm an operator sees. High head pressure combined with heavy purge activity is a classic Type 3 exam scenario. The reverse case: continuous excessive moisture collecting in the purge unit points to water entering through leaking tubes, not air.
Moisture, rust, and acid in R-123 systems
Moisture is the primary cause of acid formation in centrifugal chiller systems; before acid, it shows up as rust on the steel shell and tube sheets and as sludge in the oil. Water vapor combined with R-123 at operating temperature forms hydrochloric and hydrofluoric acid, damaging bearings, motor windings, and expansion devices. Technicians monitor the oil acid number and refrigerant moisture content; above specification, the fix is filter drier replacement and refrigerant processing, or off site reclamation when contamination is severe.
Frequently asked questions about the EPA 608 Type 3 exam
Is this EPA 608 Type 3 practice test free?
Yes. All 50 Type 3 questions on this page are free with instant scoring and explanations, no signup. A free account unlocks all 604 verified questions and the weak spot chart; Pro ($14.99 lifetime) adds AI Tutor and timed simulation.
What is Type 3 on the EPA 608 exam?
Type 3 covers low pressure appliances, mainly large centrifugal chillers running R-123 at or below atmospheric pressure, where a leak draws air in rather than releasing refrigerant. The EPA 608 practice test hub links every section.
What refrigerants do low pressure systems use?
R-123 is the primary active refrigerant; R-11 is fully phased out; R-1233zd is an HFO alternative with an A1 ASHRAE rating. All three operate below atmospheric pressure, which is what makes a system low pressure under Section 608.
Do you need Type 3 to repair an R-22 chiller?
No. An R-22 or R-410A chiller is a high pressure appliance, so the technician needs Type 2 or Universal certification. Type 3 applies only to low pressure equipment such as R-123 centrifugal chillers.