The Thermactor emission control system makes use of a belt-driven air pump to inject fresh air into the hot exhaust stream through the engine exhaust ports. The result is the extended burning of those fumes which were not completely ignited in the combustion chamber, and the subsequent reduction of some of the hydrocarbon and carbon monoxide content of the exhaust emissions into harmless carbon dioxide and water.
The Thermactor system is composed of the following components:
- Air supply pump (belt-driven)
- Air bypass valve
- Check valves
- Air manifolds (internal or external)
- Air supply tubes (on external manifolds only)
Air for the Thermactor system is cleaned by means of a centrifugal filter fan mounted on the air pump driveshaft. The air filter does not require a replaceable element.
To prevent excessive pressure, the air pump is equipped with a pressure relief valve which uses a replaceable plastic plug to control the pressure setting.
The Thermactor air pump has sealed bearings, which are lubricated for the life of the unit, and preset rotor vane and bearing clearances, which do not require any periodic adjustments.
The air supply from the pump is controlled by the air bypass valve, sometimes called a dump valve. During deceleration, the air bypass valve opens, momentarily diverting the air supply through a silencer and into the atmosphere, thus preventing backfires within the exhaust system.
A check valve is incorporated in the air inlet side of the air manifolds. Its purpose is to prevent exhaust gases from backing up into the Thermactor system. This valve is especially important in the event of drive belt failure and during deceleration, when the air bypass valve is dumping the air supply.
The air manifolds and air supply tubes channel the air from the Thermactor air pump into the exhaust ports of each cylinder, thus completing the cycle of the Thermactor system.
The Thermactor system used on cars with catalytic converters incorporates several components to prevent excessive converter temperatures from developing. Since the catalyst requires large quantities of oxygen to function, an air bypass valve and a Vacuum Differential Valve (VDV) are used to control temperatures by dumping air from the Thermactor pump to the atmosphere instead of delivering it to the catalyst.
The purpose of these valves is to "dump" air during periods of vacuum failure, the rich exhaust gas condition during deceleration, prevent backfire when the exhaust gases are overly rich and provide pressure relief (due to excessive air pump volume or restriction downstream).
The air bypass valve used with catalytic converters differs from the valve used on cars without converters and can be identified by the vacuum port on top of the valve. The valve functions as follows: during normal operation, engine intake manifold vacuum applied through the VDV holds the valve upward, allowing the Thermactor air to flow to the cylinder head(s) and blocking the vent port. When engine intake manifold vacuum rises or drops sharply (such as during acceleration or deceleration, or system blockage or failure), the VDV operates and momentarily cuts off the vacuum to the bypass valve. The spring pulls the stem down, seating the valve to cut off the pump air to the exhaust manifold, and opening the dump valve at the lower end of the bypass valve to momentarily divert the pump air to the atmosphere. In the case of excess pump volume or a downstream restriction, the excess pressure will unseat the valve in the lower portion of the bypass valve and allow a partial flow of pump air to the atmosphere. At the same time, the valve in the upper part of the bypass is still unseated, allowing a partial flow of pump air to the exhaust manifold to meet system requirements.
The Vacuum Differential Valve (VDV) controls the operation of the new bypass valve used with catalytic converter equipped systems.
The VDV is inserted in the vacuum control line to the bypass valve and serves to cut off the vacuum and de-energize the bypass valve. The differential valve consists of a diaphragm connected to a dump valve that controls the vacuum to the bypass valve. During normal operation, vacuum is equalized on both sides of the diaphragm and the spring holds the dump valve closed. When sudden higher than normal vacuum is encountered, such as under deceleration conditions, vacuum is higher on the dump valve side of the diaphragm and the diaphragm operates the dump valve. As the dump valve operates, the vacuum signal to the bypass valve is diverted through the built-in filter system to the atmosphere. When the vacuum bleeding through the bypass timing orifice in the VDV has equalized on both sides of the diaphragm, the diaphragm return spring once again closes the dump valve and applies vacuum to the bypass valve, which again applies pump air to the exhaust ports.
Before performing an extensive diagnosis of the emission control systems, verify that all specifications on the Certification Label are met, because the following systems or components may cause symptoms that appear to be emission related.
- Improper vacuum connections
- Vacuum leaks
- Ignition timing
- Plugs, wires, cap and rotor
- Carburetor float level
- Carburetor main metering jets
- Choke operation
In order to test the three major components of a Thermactor system (air pump, check valve and bypass valve), a pressure gauge and adapter are required. The adapter can be fabricated as follows:
- Obtain these items:
- 1 / 2 -inch pipe tee
- 1 / 2 -inch pipe, 2 inches long and threaded at one end
- 1 / 2 -inch pipe plug
- 1 / 2 -inch reducer bushing or other suitable gauge adapter
- Apply the sealer to the threaded ends of the pipe, plug and bushing. Assemble the adapter as shown in the illustration.
- Drill a 11 / 32 inch (0.3437) diameter hole through the center of the pipe plug. Clean out the chips after drilling.
- Attach the pressure gauge with 1 / 4 -psi increments to the bushing or adapter.
BELT TENSION AND AIR LEAKS
- Before proceeding with the tests, check the pump drive belt tension to see if it is within specifications.
- Turn the pump by hand. If it has seized, the belt will slip, producing noise. Disregard any chirping, squealing, or rolling sounds from inside the pump; these are normal when it is turned by hand.
- Check the hoses and connections for leaks. Hissing or a blast of air is indicative of a leak. Soapy water, applied lightly around the area in question, is a good method for detecting leaks.
- Disconnect the air supply hose at the anti-backfire valve.
- Connect a vacuum gauge, using a suitable adapter, to the air supply hose.
If there are two hoses plug the second one.
- With the engine at normal operating temperature, increase the idle speed and watch the vacuum gauge.
- The air flow from the pump should be steady and fall between 2-6 psi. If it is unsteady, or falls below this, the pump is defective and must be replaced.
The air pump is normally noisy; as engine speed increases, the noise of the pump will rise in pitch. The rolling sound the pump bearings make is normal; however, if this sound becomes objectionable at certain speeds, the pump is defective, and will have to be replaced.
A continual hissing sound from the air pump pressure relief valve at idle indicates a defective valve. Replace the relief valve.
If the pump rear bearing fails, a continual knocking sound will be heard. Since the rear bearing is not separately replaceable, the pump will have to be replaced as an assembly.Check Valve Test
- Before starting the test, check all of the hoses and connections for leaks.
- Detach the air supply hose(s) from the check valve(s).
- Insert a suitable probe into the check valve and depress the plate. Release it; the plate should return to its original position against the valve seat. If binding is evident, replace the valve.
- Repeat Step 3 if two valves are used.
- With the engine running at normal operating temperature, gradually increase its speed to 1,500 rpm. Check for exhaust gas leakage. If any is present, replace the valve assembly.
Vibration and flutter of the check valve at idle speed is a normal condition and does not mean that the valve should be replaced.Air Bypass Valve Test
- Detach the hose, which runs from the bypass valve to the check valve, at the bypass valve hose connection.
- Connect a tachometer to the engine. With the engine running at normal idle speed, check to see that air is flowing from the bypass valve hose connection.
- Speed the engine up, so that it is running at 1,500-2,000 rpm. Allow the throttle to snap shut. The flow of air from the bypass valve at the check valve hose connection should stop momentarily and air should then flow from the exhaust port on the valve body or the silencer assembly.
- Repeat Step 3 several times. If the flow of air is not diverted into the atmosphere from the valve exhaust port, or if it fails to stop flowing from the hose connection, check the vacuum lines and connections. If these are tight, the valve is defective and requires replacement.
REMOVAL & INSTALLATION
- Loosen the air pump adjusting bolt. Loosen the air pump-to-mounting bracket bolt and push the air pump toward the cylinder block. Remove the belt.
Thermactor Air Pump
- Disconnect the air outlet hose at the air pump.
- Loosen the pump belt tension adjuster.
- Disengage the drive belt.
- Remove the mounting bolt and air pump.
- Position the air pump on the mounting bracket and install the mounting bolt.
- Place the drive belt in the pulleys and attach the adjusting arm to the air pump.
- Adjust the drive belt tension to specifications and tighten the adjusting arm and mounting bolts.
- Connect the air outlet hose to the air pump.
- Loosen the air pump adjusting arm bolt and mounting bracket bolt to relieve drive belt tension.
- Remove the drive pulley attaching bolts and pull the drive pulley off the air pump shaft.
- Pry the outer disc loose, then pull off the centrifugal filter fan with slip-joint pliers.
- Install a new filter fan by drawing it into position, using the pulley and bolts as an installer. Draw the fan evenly by alternately tightening the bolts, making certain that the outer edge of the fan slips into the housing.
A slight interference with the housing bore is normal. After a new fan is installed, it may squeal upon initial operation, until its outer diameter sealing lip has worn in, which may require 20 to 30 miles of operation.Thermactor Check Valve
- Disconnect the air supply hose at the valve. (Use a 1 1 / 4 inch crowfoot wrench; the valve has standard, right-hand pipe thread.)
- Clean the threads on the air manifold adapter (air supply tube on V8 engine) with a wire brush. Do not blow compressed air through the check valve in either direction.
- Install the check valve and tighten it.
- Connect the air supply hose.
- Disconnect the air and vacuum hoses at the air bypass valve body.
- Position the air bypass valve and connect the respective hoses.