See Figures 1 and 2
The thermactor air injection system reduces carbon monoxide and hydrocarbon content of exhaust gases by injecting fresh air into the exhaust gas stream as it leaves the combustion chambers. A belt driven air pump supplies air to the exhaust port near the exhaust valve, by either an external manifold or internal drilled passages. The oxygen in the fresh air plus the heat of the exhaust gases causes burning which converts exhaust gases to carbon dioxide and water vapor.
The air supply pump is a positive displacement, vane type that is available in 11 cu. in. and 19 cu. in. sizes, either of which may be driven with different pulley ratios for different applications. The 11 cu. in. pump receives its air through a remote filter attached to the air inlet nipple or through an impeller type centrifugal air filter fan. The 19 cu. in. pump uses an impeller type centrifugal air filter fan which separates dirt, dust and other contaminants from the intake air by centrifugal force. The air supply pump does not have a pressure relief valve, a function performed by the bypass valve. There are two general groups of air bypass valves, normally closed and normally open. Each group is available in remote (inline) versions or pump mounted versions. The bypass valves are part of the thermactor system.
Normally closed valves supply air to the exhaust system with medium and high applied vacuum signals during normal operating modes, short idles and some accelerations. With low or no vacuum applied, the pump air is dumped through the silencer ports of the valve. Normally open air bypass valves are available with or without vacuum vents and testing procedures are different for each type. Normally open valve with a vacuum vent provide a timed air dump during decelerations and also dump when a vacuum pressure difference is maintained between the signal port and the vent port. The signal port must have 3 in. Hg more vacuum than the vent port to hold the dump. This mode is used to protect the catalyst from overheating. Normally open valves without a vacuum vent provide a timed dump of air for 1-3 seconds when a sudden high vacuum of about 20 in. Hg is applied to the signal port to prevent backfire during deceleration.
In addition the bypass valves, an air supply control valve is used to direct air pump output to the exhaust manifold or downstream to the catalyst system depending upon the engine control strategy. A combination air bypass/air control valve combines the functions of the air bypass valve and the air control valve into a single unit. There are two normally closed valves, the non-bleed type and the bleed type, all of which look alike. One distinguishing feature will be that the bleed type will have the percent of bleed molded into the plastic case.
Finally, the air check valve is a one-way valve that allows thermactor air to pass into the exhaust system while preventing exhaust gases from passing in the opposite direction. The pulse air valve replaces the air pump application in some thermactor systems. It permits air to be drawn into the exhaust system on vacuum exhaust pulses and blocks the backflow of high pressure exhaust pulses. The fresh air completes the oxidation of exhaust gas components. Although the two valves share the same basic part number and have the same appearance, they are not interchangeable.
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 3
- 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.
See Figure 4
- 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 5
- 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 6
- 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 Figure 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 8-10 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 Figures 8 and 9
- 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
Thermactor Air Pump
- Disconnect the negative battery cable.
- Tag or mark the hoses attached to the air pump.
- Loosen the hose clamps and remove the hoses attached to the pump assembly. Inspect the hoses for cracks tears or any sign of wear and replace the hose(s) if needed.
- Remove the air pump drive belt. Inspect for excessive wear and replace if needed.
- Loosen and remove the air pump adjuster bracket bolt. Rotate the adjuster bracket out of the way.
- Loosen and remove the air pump retainer nut and bolt. With the bolt removed, carefully remove the air pump from the engine compartment. Depending on the age of the engine, a small prytool may be needed to aid in removing the pump assembly from the engine.
- Position the air pump into the engine compartment and secure in place with the retainer nut and bolt. Tighten the nut only hand-tight at this time.
- Rotate the air pump bracket into position on the pump body and secure in place with the retainer bolt. Install the drive belt on the pump pulley, Tension the belt, and tighten the bracket bolt to 22-32 ft. lbs (29-42 Nm).
- Connect the hoses to the air pump and secure with the hose clamps.
- Connect the negative battery cable.
- Tag or mark each hose attached to the air valve to be removed.
- If the hose is secured to the valve with a hose clamp, loosen the clamp before removing. Remove the hoses from the air valve and inspect for wear. Replace the hose if needed.
- Remove the air valve from the engine.
- If installing a new air valve, compare the replacement valve with the original valve to make sure they are similar.
- Position the air valve in the engine compartment and attach the hoses to the valve in the correct order. If equipped, secure the hose in place using the hose clamp removed earlier.
- Start the engine and check for any vacuum leaks.