See Figure 1
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 by pass 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 pre-set rotor vane and bearing clearances, which do not require any periodic adjustments.
The air supply from the pump is controlled by the air by-pass valve, sometimes called a dump valve. During deceleration, the air by-pass 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 by-pass 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.
Air Pump Functional Check
Check the air pump belt tension and adjust it, if necessary. Disconnect the air supply hose from the bypass control valve. The pump is operating properly if air flow is felt at the pump outlet and the flow increases as the engine speed is increased. Do not pry on the pump to adjust the belt as the aluminum housing is likely to collapse.Normally Closed Bypass Valve Check
See Figure 2
- Disconnect the air supply hose at the valve outlet.
- Remove the vacuum line to check to see that a vacuum signal is present at the vacuum nipple. Remove or bypass any restrictors or delay valves in the vacuum line. There must be a vacuum present at the nipple before proceeding.
- With the engine at 1,500 rpm and the vacuum line connected to the vacuum nipple, air pump supply air should be heard and felt at the air bypass valve outlet.
- With the engine at 1,500 rpm, disconnect the vacuum line. Air at the outlet should be significantly decreased or shut off. Air pump supply air should be heard or felt at the silencer ports.
- If the normally closed air bypass valve does not successfully complete the above tests, check the air pump. If the pump is operating properly, replace the air bypass valve.
WITH VACUUM VENT
See Figure 3
- Disconnect the air pump supply line at the outlet.
- Disconnect all vacuum lines from the vacuum nipple and the vacuum vent.
- Start the engine and raise the engine speed to 1,500 rpm. The air pump supply air should be heard and felt at the outlet.
- Using a length of vacuum hose with no restrictors or devices, connect the vacuum nipple to one of the manifold vacuum fittings on the intake manifold. With the vacuum vent open to the atmosphere and the engine at 1,500 rpm, virtually no air should be felt at the valve outlet and virtually all air should be bypassed through the silencer ports.
- Using the same direct vacuum line to an intake manifold vacuum source, cap the vacuum vent. Accelerate the engine speed to 2,000 rpm and suddenly release the throttle. A momentary interruption of air pump supply air should be felt at the valve outlet.
- Reconnect all vacuum and Thermactor lines. If any of the above tests are not satisfactorily completed, check the air pump. If the air pump is operating properly, replace the bypass valve.
See Figure 4
- Disconnect the air supply line at the valve outlet.
- Disconnect the vacuum line at the vacuum nipple.
- With the engine at 1,500 rpm, air should be heard and felt at the valve outlet.
- Connect a direct vacuum line that is free from restrictions from any manifold vacuum source to the vacuum nipple on the air bypass valve. Air at the outlet should be momentarily decreased or shut off.
- Air pump supply air should be heard or felt at the silencer ports during the momentary dump. Restore all original connections. If any of the above tests are not as described, check the air pump. If the air pump is operating properly, replace the bypass valve.
See Figure 5
- Verify that air flow is being supplied to the valve inlet by disconnecting the air supply hose at the inlet and verifying the presence of air flow with the engine at 1,500 rpm. Reconnect the air supply hose to the valve inlet.
- Disconnect the air supply hoses at outlets A and B .
- Remove the vacuum line at the vacuum nipple.
- Accelerate the engine speed to 1,500 rpm. Air flow should be heard and felt at outlet B with little or no air flow at outlet A .
- With the engine at 1,500 rpm, connect a direct vacuum line from any manifold vacuum fitting to the air control valve vacuum nipple. Air flow should be heard and felt at outlet A with little or no air flow at outlet B .
- If the valve is the bleed type, less air will flow from outlet A or B and the main discharge will change when vacuum is applied to the vacuum nipple.
- Restore all connections. If the test results are not as described, replace the air control valve.
See Figures 6 and 7
The combination air bypass/air control valve combines the functions of the air bypass and air control valve into a single unit. There are two normally closed valves; the non-bleed and bleed type, both of which look alike. One distinguishing feature will be that the bleed type will have the percent of bleed molded into the plastic case.
- Disconnect the hoses from outlets A and B .
- Disconnect and plug the vacuum line to port D .
- With the engine operating at 1,500 rpm, air flow should be noted coming out of the bypass vents.
- Reconnect the vacuum line to port D and disconnect and plug the vacuum line to port S . Make sure vacuum is present in the line to vacuum port D .
- With the engine operating at 1,500 rpm, air flow should be noted coming out of outlet B and no air flow should be coming from outlet A .
- With the engine at 1,500 rpm, apply 810 in.Hg of vacuum to port S . Air should now flow from outlet A .
- If the valve is the bleed type, some lesser amount of air will flow from outlet A or B and the main discharge will change when vacuum is applied to port S .
If there is a small air tap attached to the inlet tube from the air pump, air flow should be present during engine operation.Air Check Valve/Pulse Air Valve Test
See Figure 8
- Inspect all hoses, tubes and the air valve for leaks.
- Disconnect the hose on the inlet side if the air valve and attempt to blow through the valve. Air should pass freely.
- Repeat the test, only this time attempt to suck air through the valve. No air should pass.
- If any other results are obtained, replace the check valve.
REMOVAL & INSTALLATION
Air By-Pass Valve
To remove the air by-pass valve, label and disconnect the air and vacuum hoses at the air by-pass valve body, then remove the valve from the vehicle.
To install it, position the valve and connect the respective hoses.Check Valve
See Figure 9
- Disconnect the air supply hose at the valve. Use 1 1 / 4 in. crowfoot wrench. The valve has a standard, right-hand pipe thread.
- Clean the threads on the air supply tube with a wire brush. Do not blow compressed air through the check valve in either direction.
- Install the check valve and tighten.
- Connect the air supply hose.
- Loosen the air pump attaching bolts.
- Remove the drive pulley attaching bolts and pull the pulley off the air pump shaft.
- Pry the outer disc loose, then remove the centrifugal filter fan. Care must be used to prevent foreign matter from entering the air intake hole, especially if the fan breaks during removal. Do not attempt to remove the metal drive hub.
- Install the new filter fan by drawing it into position with the pulley bolts.
- 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 pulley and attach the adjusting arm to the air pump.
- Adjust the drive belt tension and tighten the adjusting arm and mounting bolts.
- Connect the air outlet hose to the air pump.
Do not disassemble the air pump on the truck to replace the relief valve, but remove the pump from the engine.
- Remove the relief valve on the pump housing and hold it in position with a block of wood.
- Use a hammer to lightly tap the wood block until the relief valve is seated.
- Compress the locking tabs inward (together) and remove the plastic pressure-setting plug.
- Before installing the new plug, be sure that the plug is the correct one. The plugs are color-coded.
- Insert the plug in the relief vale hose and push in until it snaps into place.