How to Use AUTOOL LM150 Digital Manifold Gauge

Use the AUTOOL LM150 by verifying the refrigerant and vehicle procedure, closing both V-shaped manifold valves, checking every hose and adapter, installing four AA batteries, selecting the correct refrigerant and units, and zeroing both disconnected pressure channels at atmosphere. Map the two wired temperature clamps to the specified low- and high-side pipe locations, then capture both pressures, saturation temperatures, pipe temperatures, superheat and subcooling under one stable operating condition.

The LM150 is a dual-pressure, dual-temperature digital manifold with 93 refrigerant datasets, relative-vacuum mode and a timed pressure-change test. It supports controlled A/C measurement and service, but it cannot identify an unknown refrigerant, choose a vehicle charge mass, prove deep evacuation or locate a leak by itself.

Updated August 27, 2026.

What the LM150 displays

The AUTOOL LM150 measures low- and high-side gauge pressure simultaneously. Once the correct refrigerant is selected, it converts those pressures into evaporation (EV) and condensation (CO) saturation temperatures. With T1 and T2 clamped to the correct pipes, it also displays pipe temperatures and calculates superheat (SH) and subcooling (SC).

The manual lists a -101 kPa to 6 MPa overall measurement span and a 10 MPa overload limit, but neither overrides a lower hose or adapter working rating. The lowest-rated component controls. Its 93-dataset list is reference information, not automatic refrigerant identification.

Before you start

Open the AUTOOL manual download center and match the LM150 manual to the physical controls. Obtain verified refrigerant identity, service-port layout, charge specification, operating test condition, recovery method, evacuation target and pressure-test rule from the vehicle or equipment procedure.

Inventory the actual kit: main unit, red/blue/yellow hoses, two wired temperature clamps, adapters and case. Check connector compatibility and hose working pressure instead of relying on color or a package illustration.

Use ventilation, eye and hand protection, rated low-loss couplers and compliant recovery/service equipment. Route hoses and clamp leads away from fans, belts, exhaust heat and electrical terminals.

Stop: Do not connect an unknown or contaminated system, pressure-test with oxygen or unregulated shop air, vent refrigerant to clear a hose, exceed the lowest component rating, or open either valve until the center path is traced.

LM150 manual diagram labeling screen keys valves probe socket and service ports — Map the exact keys, valves, probe socket and low, center and high ports before building the flow path.

Understand the LM150 controls

The blue V-shaped valve controls the low-side path and the red valve controls the high-side path. The lower fittings are low side, center refrigerant/vacuum connection and high side. The screen keys control Unit, Mode, Run/Stop, backlight, °C/°F, Zero, R+/R- refrigerant selection and power. Confirm the visible mode before interpreting any number.

LM150 step-by-step operating procedure

Step 1: Define the exact task

Choose running pressure-temperature diagnosis, procedure-controlled evacuation observation or an approved isolated pressure-change test. Record refrigerant, connection diagram, system state, target data, stabilization time and finish method.

Completion check: Every connection and acceptance value comes from exact vehicle or equipment information.

AUTOOL LM150 digital manifold front view — Identify the screen, blue and red V-shaped valves, sight window and three lower service ports before connection.

Step 2: Inspect the LM150 and complete pressure path

Close both V-shaped valves. Inspect the screen, sight window, pressure-release hardware, clamp sockets, brass threads, hoses, couplers, gaskets and valve stems. Replace damaged, hardened or contaminated parts and confirm working ratings.

Completion check: The full pressure path is clean, closed, compatible and rated for the expected state.

AUTOOL LM150 kit with hoses adapters case and two wired temperature clamps — Inventory both clamps, every hose and each adapter before assigning T1 and T2.

Step 3: Inventory and label both clamps

Check the two clamp connectors, leads, jaw springs and sensor surfaces. Label them T1 and T2 if needed, then record which exact pipe each channel will measure. Do not assign a function from clamp color alone.

Completion check: Both clamps and all three hose paths are unambiguous before connection.

Step 4: Install four AA batteries

Install four matched 1.5 V AA/LR6 batteries with correct polarity. Power on and verify the battery icon, complete screen segments, backlight and keys.

Completion check: The display is stable and battery condition can support the complete job.

LM150 manual page showing pressure mode refrigerant selection zeroing and connection direction — Select the verified refrigerant and units and zero both open-air channels before following the exact connection map.

Step 5: Select refrigerant and units

With both valves closed and pressure inlets disconnected, use R+/R- to select the verified refrigerant. Select the pressure and temperature units used by the service information.

Completion check: Refrigerant and units match the written job sheet exactly.

Step 6: Zero both channels at atmosphere

Leave both pressure inlets open to clean atmospheric pressure. Hold Zero until the residual high- and low-side digits return to zero. Never zero a channel with pressure or vacuum trapped in a hose.

Completion check: Both disconnected pressure channels read zero.

Step 7: Connect and map T1 and T2

Seat both probe connectors. Clamp each sensor to clean metal at the exact pipe location required by the procedure, not over insulation or a fitting. Ensure full jaw contact and route both leads safely.

Completion check: Each stable temperature reading belongs to a named pipe location.

Step 8: Hang the manifold and trace every hose

Hang the LM150 upright. Trace blue to the verified low-side port, red to high side and yellow to the required recovery, vacuum or charging equipment. Follow the vehicle and low-loss coupler instructions for connection order while both manifold valves remain closed.

Stop: If a coupler resists, a fitting leaks, a hose identity is uncertain or any hose shows damage, isolate and correct the setup.

Completion check: Every hose is traced end to end and neither valve opened unintentionally.

Step 9: Establish one repeatable operating condition

For diagnosis, set engine speed, blower/load, doors, airflow, fan command and ambient measurement exactly as required. Observe from a safe position and wait for compressor operation, pressures and temperatures to stabilize.

Completion check: The complete operating state is recorded before capturing data.

LM150 manual page showing SH SC display and relative vacuum mode — SH and SC require correct probes and refrigerant; relative vacuum remains a gross trend rather than micron acceptance.

Step 10: Capture the synchronized data set

Record low pressure, high pressure, EV, CO, T1, T2, SH and SC together. Confirm that probe mapping and screen fields agree with the required suction and liquid line locations. A believable calculated value can still be wrong when a clamp is swapped or loose.

Completion check: All eight values represent one stable condition and are compared with the exact vehicle window.

Step 11: Diagnose before moving refrigerant

Assess airflow, fan operation, compressor command, sensor data, restrictions and refrigerant condition using the vehicle sequence. Do not add or remove refrigerant simply to make one pressure familiar. When charge service is justified, recover and charge by the specified process and mass.

Completion check: Setup and control faults are separated from a refrigerant-quantity decision.

Step 12: Treat relative vacuum as a trend

Recover refrigerant first. Enter Vacuum mode and connect the center path to compliant evacuation equipment. Follow the required isolation sequence. The LM150 relative display shows gross progress; use a dedicated absolute gauge and specified decay test for micron-level acceptance.

Completion check: Evacuation is accepted by the required absolute target, stabilization and hold.

LM150 manual page showing initial pressure current pressure difference and elapsed time — Interpret pressure difference only with the approved medium, stable temperature, duration and external connection checks.

Step 13: Run the timed pressure-change test carefully

Use only the approved medium and regulated pressure. With the system stabilized and both valves positioned by the exact procedure, enter Pressure Leak Test and press Run/Stop. Record initial pressure, current pressure, delta, elapsed time and temperature.

Completion check: Medium, pressure, temperature, duration and acceptance rule are all documented.

Step 14: Isolate, disconnect and store

Stop the test, close both valves and return service equipment and vehicle to the prescribed shutdown state. Manage trapped refrigerant through compliant recovery or low-loss equipment, disconnect in the required order and restore port caps. Clean clamp surfaces and fittings, protect the ports and remove batteries for extended storage.

Completion check: No refrigerant was intentionally vented, ports are restored and the complete result is saved.

Reliable LM150 data gates

Gate	Pass condition	Stop or repeat when
Identity	Exact refrigerant and units are verified	Selection is guessed from pressure
Zero	Both channels are disconnected at atmosphere	A hose held pressure during zeroing
Clamps	T1/T2 have full contact at named pipes	A probe is loose, insulated or swapped
Condition	Load, airflow and compressor state are stable	Readings come from changing conditions
Decision	Pressure, saturation, pipe temperature, SH and SC agree with vehicle data	One value drives a charge decision

Common LM150 problems

A pressure channel will not zero

Disconnect every pressure and vacuum source, manage trapped pressure through approved equipment and let the gauge stabilize. Persistent offset requires evaluation rather than mental correction.

T1 or T2 is blank or unstable

Reseat the connector, inspect the lead and ensure the jaws contact clean metal fully. Swap channels only as a controlled check and preserve pipe identity.

SH or SC is implausible

Recheck refrigerant selection, clamp mapping, pipe location, contact, airflow and system stability before changing refrigerant quantity.

Pressure changes during the timed test

Record temperature and inspect external hoses, couplers, pads and valves. A trend does not locate a leak or prove that the vehicle circuit is responsible.

AUTOOL LM150 FAQ

How many refrigerants does LM150 support?

The exact manual lists 93 refrigerant pressure-temperature datasets.

Are two temperature clamps included?

The current package information shows two wired clamps. Verify the exact delivered kit and connector condition before the job.

Can relative vacuum replace a micron gauge?

No. Use the absolute gauge and decay criterion specified by the procedure.

What batteries does LM150 use?

Four 1.5 V AA/LR6 batteries.

The reliable LM150 workflow

Verify the job data, inspect and close both V-shaped valve paths, inventory the two-clamp kit, install four AA batteries, select the exact refrigerant and units, zero both open-air channels, map T1 and T2, trace all hoses, stabilize the system and capture pressure, saturation, pipe temperature, SH and SC together. Keep vacuum and timed modes within their limits, then isolate and disconnect without venting.