Air Conditioning troubleshooting - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Lerch1145 · 04-25-2015, 01:14 PM

Good morning, with summer fast approaching I have been working to get the A/C stystem up and running. Working through everything I noticed the heater return line from the heater core was getting as hot as the feed line. Replaced the water valve thinking this was the issue. Currently still does the same thing? Has good vacume with the A/C system is on? Is this correct? With the A/C system off the vacume stops. First roadblock of many to come.

Lurayfarmer · 04-25-2015, 08:10 PM

The valve is the most likely suspect. Vacuum should close the valve with the AC on. If just a little hot water leaks past, it will cause the heater core to fight the AC. Swapping the valve out is an easy fix.

Lerch1145 · 04-25-2015, 10:06 PM

That's the thing, I swapped out the valve with a new one with same results. Tomorrow heading after the vacuum system to check for a small leak or possible restriction.

**landy** · 04-25-2015, 10:52 PM

Mine did the same thing, even with a new hot water valve. I ended up splicing a gate valve into the hose to completely stop the flow of hot water. With the valve closed, the hose stays cool.

Lerch1145 · 04-26-2015, 04:53 PM

Replaced all A/C vacuum lines, found come crud inside lines, but still have the same issue. Also found out inside passenger kick pad valve won't open alone. If I assist it will hold open until shutdown or change to outside air. Plenum valve works great?

Andy4639 · 04-26-2015, 08:04 PM

Check the vacum head on back of the controller. There are several diferant ones. You may have the wrong one on it. Best thing is do as stated above. Put you a manual cut off valve in line with the vacum valve. This way you have no heat coming into the truck cab. Mine works great.

Lerch1145 · 04-26-2015, 08:28 PM

I wanted to replace the vacuum control switch but this seems to be a needle in the hay stack? Anyone have an idea who has this part? Got this pic from an older post.

mechanicalman · 04-26-2015, 09:36 PM

Quote:

Originally Posted by Lerch1145

Good morning, with summer fast approaching I have been working to get the A/C stystem up and running. Working through everything I noticed the heater return line from the heater core was getting as hot as the feed line. Replaced the water valve thinking this was the issue. Currently still does the same thing? Has good vacume with the A/C system is on? Is this correct? With the A/C system off the vacume stops. First roadblock of many to come.

Try removing the vacuum hose, and if that works then you probably have the wrong water valve. WAG.

04-25-2015, 01:14 PM	#1
Lerch1145 Registered User Join Date: Oct 2014 Location: Savannah, GA Posts: 82	Air Conditioning troubleshooting Good morning, with summer fast approaching I have been working to get the A/C stystem up and running. Working through everything I noticed the heater return line from the heater core was getting as hot as the feed line. Replaced the water valve thinking this was the issue. Currently still does the same thing? Has good vacume with the A/C system is on? Is this correct? With the A/C system off the vacume stops. First roadblock of many to come. __________________ 1972 GMC 2500 2007 Chevrolet Silverado 1500

04-25-2015, 08:10 PM	#2
Lurayfarmer Registered User Join Date: Mar 2014 Location: Luray, VA Posts: 73	Re: Air Conditioning troubleshooting The valve is the most likely suspect. Vacuum should close the valve with the AC on. If just a little hot water leaks past, it will cause the heater core to fight the AC. Swapping the valve out is an easy fix. __________________ Bill Shenandoah Valley of Va 1972 GMC 2500 Sierra Grande 402, Custom Camper Package

04-25-2015, 10:06 PM	#3
Lerch1145 Registered User Join Date: Oct 2014 Location: Savannah, GA Posts: 82	Re: Air Conditioning troubleshooting That's the thing, I swapped out the valve with a new one with same results. Tomorrow heading after the vacuum system to check for a small leak or possible restriction. __________________ 1972 GMC 2500 2007 Chevrolet Silverado 1500

04-25-2015, 10:52 PM	#4
landy Senior Member Join Date: Jun 2000 Location: alb, nm Posts: 413	Re: Air Conditioning troubleshooting Mine did the same thing, even with a new hot water valve. I ended up splicing a gate valve into the hose to completely stop the flow of hot water. With the valve closed, the hose stays cool.

04-26-2015, 04:53 PM	#5
Lerch1145 Registered User Join Date: Oct 2014 Location: Savannah, GA Posts: 82	Re: Air Conditioning troubleshooting Replaced all A/C vacuum lines, found come crud inside lines, but still have the same issue. Also found out inside passenger kick pad valve won't open alone. If I assist it will hold open until shutdown or change to outside air. Plenum valve works great? __________________ 1972 GMC 2500 2007 Chevrolet Silverado 1500

04-26-2015, 08:04 PM	#6
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Air Conditioning troubleshooting Check the vacum head on back of the controller. There are several diferant ones. You may have the wrong one on it. Best thing is do as stated above. Put you a manual cut off valve in line with the vacum valve. This way you have no heat coming into the truck cab. Mine works great. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

04-26-2015, 08:28 PM	#7
Lerch1145 Registered User Join Date: Oct 2014 Location: Savannah, GA Posts: 82	Re: Air Conditioning troubleshooting I wanted to replace the vacuum control switch but this seems to be a needle in the hay stack? Anyone have an idea who has this part? Got this pic from an older post. Attached Images __________________ 1972 GMC 2500 2007 Chevrolet Silverado 1500

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