| [GMCnet] A/C, and heater vacuum controls. [message #332541] |
Fri, 25 May 2018 00:22  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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This vacuum control system isn't my strong suit. It's a 78 system. Used my hand held vacuum pump in checking the system. Line from engine intake manifold, to the vacuum tank checked OK. The vacuum tank had no external leaks. But seemed to have internal valve issues of some kind. Took the tank off the 73. Tested fine. Put it in tomorrow. Or I need to find that tank that was on the burned 78 GMC. Seem to have a small leak at the dash control. That's not going to be simple to find. Thinking of applying extremely low air pressure ( Under 1 lbs. ) to the system. Then spray soppy water on the controls to find the leak.. The vacuum line from the engine to the tank is about 4 ft long. It's extremely small, and fragile due to age. Any down side of replacing that small plastic line with a larger rubber hose? HELP. Bob Dunahugh
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| Re: [GMCnet] A/C, and heater vacuum controls. [message #332548 is a reply to message #332541] |
Fri, 25 May 2018 10:21  |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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BTDT about a hundred times, Bob. Be sure and use VACUUM hose, as the small windshield washer tubing (that best fits that plastic tubing) will collapse under vacuum after it gets hot.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] A/C, and heater vacuum controls. [message #332550 is a reply to message #332548] |
Fri, 25 May 2018 10:31 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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And the best way to find those leaks is to smoke the system. The smokers were expensive when the shop I worked in bought one, but well worth the investment for a commercial shop. Today's cars use less vacuum controls, so the price has probably gone up on them. A shop that does emission control work should have one you can bribe them to use or borrow. It utilizes baby oil and very low pressure so it doesn't overpressurize the vacuum system. Very useful for finding intake system leaks also, but don't let it coat a MAF sensor unless you clean the sensor BEFORE you energize it.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] A/C, and heater vacuum controls. [message #332590 is a reply to message #332541] |
Fri, 25 May 2018 22:40 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Senior Member |
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I can pump up a vacuum a little. But the system can't hold it. Bob Dunahugh
________________________________
From: Bob Dunahugh
Sent: Friday, May 25, 2018 12:22 AM
To: gmclist@list.gmcnet.org
Subject: A/C, and heater vacuum controls.
This vacuum control system isn't my strong suit. It's a 78 system. Used my hand held vacuum pump in checking the system. Line from engine intake manifold, to the vacuum tank checked OK. The vacuum tank had no external leaks. But seemed to have internal valve issues of some kind. Took the tank off the 73. Tested fine. Put it in tomorrow. Or I need to find that tank that was on the burned 78 GMC. Seem to have a small leak at the dash control. That's not going to be simple to find. Thinking of applying extremely low air pressure ( Under 1 lbs. ) to the system. Then spray soppy water on the controls to find the leak.. The vacuum line from the engine to the tank is about 4 ft long. It's extremely small, and fragile due to age. Any down side of replacing that small plastic line with a larger rubber hose? HELP. Bob Dunahugh
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