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1964 Corvette: Service Bulletin: Lack of Heat with Controls in Full "On" Position

Subject:   Lack of Heat with Controls in Full "On" Position
Model and Year:   1964 Corvette with Air Conditioning
Source:  Chevrolet Technical Service Bulletin
Bulletin No:  TSB #1012
Section:   I
Date:  July 6, 1964


A few early 1964 Corvettes with RPO C60 Air Conditioning may have been built with a faulty vacuum control valve.  The vacuum control valve normally acts as an on-off control for the vacuum operated water shut-off valve.  Proper control operation should allow vacuum flow to the water shut-off in all control positions except "off".

Those heaters equi9pped with a faulty valve will have vacuum flow in the low and mid-heat ranges, but will experience vacuum shut-off in the maximum heat position.

A test procedure for checking the vacuum control is outlined on Page 2 of this bulletin.  If this test indicates a faulty valve rather than plugged or leaking hoses or cable misadjustment, the condition can be corrected by installing a new control valve, Part No. 3839651.

All Corvettes built after serial number S104235 have the proper valve installed at assembly.


If no heat is available through the heater with the temperature control pulled to its maximum heat position, with the engine running, remove the vacuum hose from the water shut-off valve on the firewall.  if the valve is functioning correctly, there will be no vacuum at the hose with the control in the "off" position and full vacuum with the control in the low, medium and maximum heat positions.  If there is no vacuum with the control in the maximum heat position, the control valve is faulty.

Plugged or leaking hoses would be indicated by little or no vacuum in any position.  Improper adjustment would be evidenced by excessive cable motion before start-of-vacuum or if full cable movement is restricted.

If testing indicates that the vacuum control valve is at fault, replace the valve with a new Part No. 3839651 valve.  The glove compartment must be removed to provide access for valve replacement.

Refer to Page 13-44 of the 1964 Corvette shop manual Supplement under the heading HEATER COMPONENTS for a description of system operation.


Part No:  3839651

No. Required:  1

Description:  Switch Assembly - Vacuum Control

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