To diagnose an absorption refrigerator, cut the heat first, then read what each part is doing: which are hot, which are cold, what the gauge shows, and whether there is any smell. A smell means a leak and the machine is shut down and ventilated before anything else; weak cooling usually traces to air in the circuit, a hot absorber, too little ammonia, or a blocked restriction.
Part of Refrigeration
Faults of a heat-driven ammonia-water refrigerator, how to tell them apart by pressure, temperature and smell, and which are safe to work on.
The Order Of Checks Matters More Than The List Of Faults
The corpus carrier gives a six-row table: no cooling, weak cooling, generator overheats, absorber too hot, ammonia smell, and gurgling or hammering. This page keeps those and adds the order to check them in and what each reading means. Always begin by taking the heat away, because the fire is the one input you can remove, and a charged machine in a fault state is a pressure vessel under a fire.
Symptom, Probable Cause And First Check
| Symptom | Probable cause | First check | Action |
|---|---|---|---|
| Smell of ammonia | Leak | Gauge falling, soap bubbles at joints | Cut the heat, ventilate, shut down; locate the leak from upwind |
| No cooling at all | No circulation, a blockage or too little heat | Is the generator hot? Does the condenser warm? | Increase heat if the generator is cold; look for a blocked line if it is hot and the condenser stays cool |
| Weak cooling | Low charge, hot condenser, air in the system | High-side pressure higher than the condenser temperature suggests means air | Add solution, improve condenser airflow, purge air |
| Generator overheats | Too much heat, or the outlet is blocked | Compare heat input with the pressure reading | Reduce heat; check the outlet pipe |
| Absorber too hot | Poor cooling, or weak-solution return blocked | Is the absorber cooler than the generator by a wide margin? | Add fan or water drip; clear the return line |
| Gurgling or hammering | Liquid in gas lines, wrong charge | Listen for a pattern tied to the heating cycle | Check level and lines |
The carrier’s table gives the causes and fixes. The “first check” column is the diagnostic order. A rise in high-side pressure out of proportion to the condenser temperature is the standard sign of a gas that does not condense, such as air (recalled behaviour, flagged).
What You Need
- A pressure gauge on the high side, rated for ammonia (see Pressure Gauge).
- Soapy water and a brush for leaks, as the carrier says.
- Thermometers or your hand on the pipes, with a hot-skin warning: parts that look cool can be hot.
- An indicator for vapour: a strip of red cabbage paper or other pH indicator, wetted, shifts toward its alkaline colours in ammonia vapour (see pH Testing for the colour sequence). It shows the vapour is present, not how much.
- The machine’s log, with last week’s readings.
Method: Read The Machine
Step 1: Cut the heat. Remove the fire or the bath. Leave the cooling running.
Step 2: Smell upwind, from a distance. If you smell ammonia, ventilate and treat it as a leak first.
Step 3: Compare the parts. When it is going right: generator hot, condenser warm, evaporator cold, absorber warm but clearly cooler than the generator. Any part that breaks that pattern is the lead.
Step 4: Compare the gauge with the logged normal. High pressure with a warm condenser points to air or a hot sink; low pressure with a cold generator points to too little heat or a leak.
Step 5: Change one thing at a time and wait a full cycle. Two changes together tell you nothing.
Worked Example: Reading A Pressure That Disagrees With The Temperature
Qualitative. If the condenser is cool to the hand, the ammonia vapour in it should be at a pressure matching that low temperature. If the gauge shows a pressure well above what the same fluid would give at the condenser’s temperature (read from the ammonia property table, not guessed), something in the high side is not condensing, which is the sign of air. The cure is a purge at the highest point of the high side, done outdoors, upwind, with the operator not breathing the discharge, and followed by checking the joints that let the air in. No figure is given here because the reading depends on the fluid’s own pressure-temperature data.
Common Mistakes
- Hunting a leak with a flame. Never use a flame near ammonia; it is flammable in a band of air, and the older practice of burning a sulfur stick to see white fumes does exactly that. Use soap and a wet indicator strip.
- Opening a warm, charged joint to look inside. It releases the contents at you.
- Adding more heat to cure weak cooling. If the cause is air or a hot absorber, more heat raises the pressure and fixes nothing.
- Topping up with plain water. It dilutes the solution and the gap between strong and weak shrinks; see Ammonia-Water System.
Safety
A fault is the most dangerous moment for a heated ammonia vessel
A blocked line plus a fire raises the pressure; a leak plus a closed room fills it with irritant and flammable vapour. Cut the heat first, approach from upwind, and do not enter a space that smells strongly of ammonia without help and a way out. The carrier gives 2,500 ppm as potentially fatal within 30 minutes. Never open or repair a charged circuit. See Ammonia Toxicity.
What’s Next
- Learn next: Ammonia Toxicity — what to do about the leak itself
- Combine with: Pressure Vessels — why the relief device is the last line of defence