Acid Burnout & Grounded Compressors — The Real Cleanup Protocol (Plus the Filter-Drier Follow-Up Most Techs Skip)

It's early cooling season. The first 90-degree afternoon hits, the system has been sitting most of the winter, and your phone rings: "AC isn't cooling." You pull up, hit the disconnect, megger the compressor, and the reading shows continuity to ground. Grounded compressor. Game over for that motor — but how you handle the next two hours decides whether the customer's new compressor lasts ten years or ten months.

This guide is the cleanup protocol that protects the replacement compressor (and your warranty). It covers what acid burnout actually is, why a grounded compressor almost always means acid in the lines, the full system cleanup procedure, and the one step most techs skip — the 24-72 hour return visit to swap the suction-line drier.

What "Acid Burnout" Actually Means

A compressor burnout is a motor failure inside the sealed shell. The windings overheat, the insulating varnish breaks down, and the copper either shorts winding-to-winding or shorts winding-to-shell (a ground fault). When that happens, the refrigerant and the oil that's been circulating through the compressor get cooked. Heat plus electric arcing breaks them down into hydrochloric acid (HCl) and hydrofluoric acid (HF), depending on the refrigerant.

Once those acids form, they don't stay in the compressor — they circulate through every inch of copper, every brazed joint, the metering device, the evaporator, and the line set. They will attack copper and brass over time, and they will eat the windings of the new compressor you're about to install. That's how a warranty replacement turns into a callback six months later.

How to Confirm a Grounded Compressor

1. Pull the disconnect. Verify zero volts at the compressor terminals.
2. Discharge the run capacitor. 240V across a cap will ruin your day and your meter.
3. Remove the terminal cover and the three motor leads (C, S, R) so you can read the windings clean, with no parallel path back through the contactor or capacitor.
4. Megohmmeter test (best): 500V or 1000V megger between each terminal and the compressor shell or ground. Readings below 20 megohms are suspect. Below 1 megohm is a hard fault. Healthy motors will read in the hundreds of megohms or open.
5. If you don't have a megger: a regular DMM on the highest ohm range, between each terminal and a clean ground point on the shell. Any reading at all — even tens of millions of ohms — is suspect; a healthy compressor reads OL (overload, open) here.

A 24V megger reading isn't a megger reading. The breakdown that causes a ground fault often only shows up at line voltage. A real 500V or 1000V megger applies enough potential to actually push through marginal insulation, which is exactly the failure mode you're trying to catch.

The Acid Test — Do It Even On "Easy" Burnouts

Acid-test kits are cheap. Roughly $15-30 for a single-shot oil sample kit (Nu-Calgon, Sporlan, Virginia KMP) and around $50-80 for an in-line acid-test core that drops into a Sporlan Catch-All shell during evacuation. Two ways to run it:

• Oil-sample kit (most common): Pull about a tablespoon of oil out of the old compressor or out of a low spot in the line set. Add the indicator solution per the kit instructions and watch the color. Yellow/blue = clean. Pink/red = acid. Most kits also have a pH strip for confirmation.
• In-line acid test core (best for severe burnouts): Install a Sporlan Catch-All shell with a HH-style core in the suction line during cleanup, then pull and replace the core after 24-72 hours of runtime. The spent core itself is acid-tested. If it's still showing acid, the system needs another cleanup pass.

Classifying the Burnout: Mild vs. Severe

Not every burnout needs the same cleanup. Classify before you commit to a procedure:

The Full Cleanup Checklist

This is the procedure for an acid-confirmed burnout. Print it, laminate it, throw it in the truck. Don't freelance the order — the recovery and triple-evac steps are what keep moisture and acid out of the new compressor.

Phase 1 — Recovery & Removal

1. Lockout/tagout at the disconnect. Verify zero volts.
2. Recover the refrigerant into a clearly-labeled contaminated recovery cylinder. Do NOT mix it with clean recovered refrigerant — you'll cross-contaminate every job you touch with that cylinder for the rest of its life.
3. Cut the suction and liquid lines at the compressor stubs. Leave enough copper for clean re-brazes.
4. Pull the old compressor. Bag the discharge and suction stubs immediately to keep the burnt oil smell out of the rest of the system (and your truck).
5. Drain a tablespoon of oil from the old compressor's suction stub into a small container — this is your acid-test sample.

Phase 2 — System Cleanup

1. Run the acid test on the oil sample. Document the result (photo of the kit next to the work order is best). If clean, proceed with a standard liquid-line drier. If acid is present, escalate to the full burnout cleanup below.
2. Flush the line set (severe burnouts only). RX-11 or equivalent flush solvent + dry nitrogen push, repeated until the discharged solvent runs clean. On long line sets or heavy contamination, just replace the line set — it's cheaper than a callback.
3. Replace the metering device. A piston/orifice can sometimes survive a flush. A TXV almost never does — the powerhead and the screen will hold contamination that releases later. Replace it.
4. Replace the liquid-line drier with an HH-style burnout-rated drier (Sporlan Catch-All C-series with HH cores, or equivalent). HH cores have a higher acid-removal capacity than standard cores.
5. Install a suction-line filter drier with a removable core (Sporlan Catch-All shell with HH-BD core, or equivalent). The suction drier is what catches the acid the system mobilizes during runtime — the liquid-line drier alone cannot. This is the step that gets skipped most often and causes 6-month repeat failures.
6. Install a sight glass with moisture indicator on the liquid line downstream of the drier. You want a visual on what's in the line during the 24-72 hour break-in.

Phase 3 — Install & Evacuation

1. Braze the new compressor in under flowing nitrogen (3-5 psig, just enough to keep oxygen out of the joint). Black scale inside the copper IS contamination and you'll be back next year.
2. Pressure-test with dry nitrogen to the high-side test pressure on the data plate (typically 400-450 psig for R-410A). Hold for 15-30 minutes.
3. Triple evacuation:
   • Pull to 500 microns. Hold. Break vacuum with dry nitrogen to ~5 psig.
   • Pull to 500 microns again. Hold. Break with nitrogen again.
   • Pull a final time to under 300 microns and verify the decay rate — under 100 microns of rise in 5 minutes after isolation is the spec most manufacturers want. Slow rise means residual moisture or a leak — keep pulling.
4. Weigh in the charge per the data plate. On TXV systems, set subcooling to the data-plate value (typically 8-14°F). On fixed-orifice systems, set superheat to the target from the manufacturer chart or the field formula.
5. Verify amperage at startup and at steady state. Both should be at or below RLA. A high startup amp on a brand-new compressor is a sign of restriction (often a partially-clogged liquid-line drier from acid already loading up — note for the follow-up).

The Follow-Up Visit Most Techs Skip

Here's the part that separates a journeyman from a tech who actually understands burnout cleanup: schedule a follow-up visit 24-72 hours after the install to replace the suction-line drier core.

Why: during the first day or two of runtime, the new compressor and the moving refrigerant flush the residual acid out of every cold spot in the system — the metering device body, the line-set elbows, the evaporator distributor — and dump it into the suction-line drier. By 24-72 hours, that drier is loaded. If you leave it in there long-term, two things happen:

1. It restricts the suction line as it loads up, dropping capacity and raising the new compressor's operating temperature.
2. It eventually saturates and lets acid flow downstream into the new compressor — which is exactly what you spent the original cleanup preventing.

The follow-up visit takes about 30 minutes:

1. Recover just enough refrigerant to drop the suction-line drier pressure to atmospheric (front-seat the suction service valve if you can; otherwise vapor-recover into the contaminated cylinder).
2. Swap the suction-drier core. On a Sporlan Catch-All shell, this is just an O-ring and a fresh HH-BD core — no brazing needed.
3. Run a second acid test on the spent core. If it still shows acid, the system needs the suction drier left in for another cycle, with another follow-up. If it's clean, you're done.
4. Evacuate the drier section to 500 microns. Open the suction valve. Recharge any vapor lost during the swap.
5. Verify amps, superheat/subcooling, and document on the invoice.

Refrigerant-Specific Acid Byproducts (Reference)

Different refrigerants produce different acids when they cook. The cleanup procedure is the same, but knowing what you're dealing with helps when you're explaining it to the customer:

Pricing the Job Honestly

A burnout cleanup is not the same job as a "compressor swap." If you're quoting it as the same labor line you're losing money and you're training the customer to expect cheap. The honest line items:

• New compressor + recharge
• Liquid-line burnout drier (HH cores)
• Suction-line drier shell + initial core
• Replacement metering device (TXV systems)
• Line-set flush or replacement (severe burnouts)
• Acid-test materials
• Triple evacuation
• Return visit: replacement suction-drier core + second acid test + post-flush charge verification
• Contaminated-refrigerant disposal surcharge

Quick-Reference Field Checklist

Tear this section off the printout and put it in the truck binder:

• ☐ Verify compressor is grounded (megger or DMM, all 3 leads to shell)
• ☐ Recover into contaminated cylinder (not your clean recovery tank)
• ☐ Pull oil sample, run acid test, photograph result
• ☐ Classify: mild vs. severe (see table above)
• ☐ Flush or replace line set (severe only)
• ☐ Replace metering device (mandatory on TXV systems)
• ☐ Install HH liquid-line drier
• ☐ Install suction-line drier with removable core
• ☐ Sight glass with moisture indicator
• ☐ Braze new compressor under flowing nitrogen
• ☐ Pressure test, then triple-evacuate to under 300 microns
• ☐ Weigh in charge per data plate
• ☐ Verify startup and steady-state amperage
• ☐ Schedule follow-up at 24-72 hours
• ☐ At follow-up: swap suction-drier core, run second acid test, document on invoice

Related Tools on HVAC IQ Pro

• Wet-Bulb & Target Superheat — Field Guide for Techs
• Superheat & Subcooling — The Complete Calculation Guide
• HVAC Age Decoder — verify the unit you're working on