72 A/c Air Conditioning Troubleshooting - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**kna4977** · 10-02-2006, 08:00 PM

I have my factory system installed and charged. The problem is it doesn't blow as cold as I think it should. The compressor runs all the time when the control is set for A/C, not sure if it is supposed to or not. The POA valve and hoses are frosty/icy with the system engaged with a lot of condensation due to engine heat when the system is turned off. The center outlet has colder air than the side vents. The water valve seems to always let water through, except on the rare occasion that I can increase vacuum to it by placing the truck in park and ideling at about 2000 rpm. In drive, under load, it has virtually no vacuum until I let off and coast which allows the air to be somewhat cooler, but not cool enough. The lack of vacuum at the water valve I believe is most likely causing heat to mix with the cool air, but like I said before as vacuum increases, the air does get colder, but still not as cold as it should be. Also, is there a way to increase vacuum on a consistent basis so that there is always enough to close the water valve? I did try to bypass the water valve to see if it the A/C was colder that way, but the truck wants to overheat. Any tips you can give me would be great!

mrein3 · 10-02-2006, 08:29 PM

LOTS of people take the vacuum controlled valve out and put an in-line, manual one in. That works the best but on a day like today here in MN I had my heat on going to work and the air on going home. The vacuum controlled one is better for that.
Do you have the factory vacuum pod that bolts to the ac box on the outside of the firewall? Is it broken? I had a car once that had a leak in that pod. It behaved like you describe. Colder with more vacuum. Almost hot without.

A POA system always has the compressor engaged with the AC on.

I think if you solve the vacuum issues you'll get cold air from all vents.

Did you get your fan speeds all squared away?

*72CSTC5* · 10-02-2006, 08:35 PM

What refrigerant are you using, r12 or 134a? Did you install all new parts or used? Did you put a new expansion valve in when you installed a/c? New drier? Let us know a little about the system so we can help you diagnose.

**kna4977** · 10-02-2006, 10:00 PM

New expansion valve, drier and lines. R-12

**kna4977** · 10-02-2006, 10:04 PM

Quote:

Originally Posted by mrein3

LOTS of people take the vacuum controlled valve out and put an in-line, manual one in. That works the best but on a day like today here in MN I had my heat on going to work and the air on going home. The vacuum controlled one is better for that.
Do you have the factory vacuum pod that bolts to the ac box on the outside of the firewall? Is it broken? I had a car once that had a leak in that pod. It behaved like you describe. Colder with more vacuum. Almost hot without.

A POA system always has the compressor engaged with the AC on.

I think if you solve the vacuum issues you'll get cold air from all vents.

Did you get your fan speeds all squared away?

Fan speeds ok. Where and how do I get a manual valve?

mrein3 · 10-02-2006, 10:33 PM

Quote:

Originally Posted by kna4977

Fan speeds ok. Where and how do I get a manual valve?

Hardware store. ANY in-line valve will work. All you need is one that is sized correctly. It is either 3/4 or 5/8. It looks ghetto but it works. And it is cheap.

Open the valve in the winter. Close it for the summer.

Aarons72s · 10-02-2006, 11:41 PM

As for the valve in the engine room on the heater hoses I think they suck! I am planning on going to the junk yard and finding one off of an astro safari. WE have 94 safari that has a really neat water shut off valve. Instead of just blocking off the water it has a bypass tube that just sends the water around the heater core. The van that it is on the air conditioner doesent work but when that valve is closed you dont get any heat from the heater core but in the winter when it opens be prepared to be roasted. Be forewarned you have to go to either a junk yard or the dealer. Not avaliable at part stores. If you want one Go to the junk yard pop the hood on the van and look at the a/c box. It looks similar to our boxes. If you have found the right year there should be a plastic valve that looks like an H with a vacum actuator on top. Hope this helps.
Aaron

**kna4977** · 10-03-2006, 08:57 AM

Quote:

Originally Posted by mrein3

Hardware store. ANY in-line valve will work. All you need is one that is sized correctly. It is either 3/4 or 5/8. It looks ghetto but it works. And it is cheap.

Open the valve in the winter. Close it for the summer.

Will the truck overheat if water doesn't circulate through the heater core?

**kna4977** · 10-03-2006, 08:59 AM

Is frost on the POA valve and associated line normal?

67chevy2wd · 10-03-2006, 09:26 AM

The heater core was never intended to help cool the engine, it is just there to give you heat from the engine. There are a lot of pickup down south that aren't even running a heating system.

**kna4977** · 10-03-2006, 11:12 AM

I increased the idle, and have the vacuum up to where it should be, and the water valve is now functioning properly. The A/C is very cold. However, the problem I have now is that the truck wants to run hot when the water valve is working. Any thoughts on what could be wrong now?

mrein3 · 10-03-2006, 01:02 PM

Quote:

Originally Posted by kna4977

I increased the idle, and have the vacuum up to where it should be, and the water valve is now functioning properly. The A/C is very cold. However, the problem I have now is that the truck wants to run hot when the water valve is working. Any thoughts on what could be wrong now?

1. A plugged or too small of a radiator.
2. Or a 4-blade fan.

If you have #2, that is the cheaper thing to try. Get a 7-blade fan with a fan clutch.

They must be fairly universal. I put the 7-blade and clutch out of my Monte in my truck.

If that doesn't work you need to think about a new and/or bigger radiator. I put a 4-core in mine and have never had a problem.

In an overheat situation, turning your fan on high will aide in cooling your coolant. When I had my old radiator and 4-blade fan I would get in situations in a traffic jam where my temp gauge would climb until I turned on the heat-full blast. It sucks to be sitting there that way but it beats the alternative. When my daily driver (94 Escort) needed a new radiator, the same trick got me home one day. Windows open, heat on full.

You may have been using your heater as extra cooling capacity and not even known it.

**kna4977** · 10-04-2006, 12:33 PM

I've got the 7 blade fan. I replenished the coolant and replaced the radiator cap today. It is still wanting to run hot, but I don't let it get there. How can I tell what part or parts are bad? It ran fine with the current radiator until a couple of days ago, so I don't think that's the problem.

How do you tell if the water pump is bad?

What about the thermostat?

Aarons72s · 10-04-2006, 01:20 PM

Id change the thermostat. Those things are cheap and one year I got a bunch of bad ones. I used to drive a 85 dodge aries and I put about 4 of those thermostats in it before I finally got one that worked. The other 4 just kept sticking and caused it to over heat. This is going to sound like a dumb question but do you have a fan shroud? On my green and white the punk I bought it from threw the fan shroud away and she would overheat. It had the clutch fan on it to with large tank 3 row radiator. Plus he didnt even put a thermostat in it. Well I took the fan shroud and factory? flex fan off my orange and white put them on the green and white and it fixed the problem.
But soon after that the tanks started to leak because the radator was rotting out. Went to local parts store and bought a new 4 row radiator I want to say for about $200 but that was also 3 years back. How old is your water pump? Where did it come from? New or rebuilt? You may want to also just change it. There cheap anyway and not that hard to change. Hope this helps. Aaron

**kna4977** · 10-07-2006, 10:49 PM

I replaced the water pump and the thermostat, but still the temp gauge wants to continue to climb higher and higher.

How do you know if air is in the system, and how do you get rid of it if it's there?

The hoses all look fine, with no kinks, and I have the right amount of coolant in it.

What should I do at this point? Do I need a larger radiator?

How much soes it cost for a head gasket replacement?

Aarons72s · 10-07-2006, 11:28 PM

How old is the clutch for the clutch fan? I know when they get old sometimes they do not engage when they get hot. That was one of the problems on my green and white. That is why I only use flex fans. As for getting the air out of the system there is a tool that ataches where the radiator cap goes and they put a vacum on it. Longhorn Man should probably be able to tell you how and where to get it done. As for the radiator due you have a 3 row or 4 row. If it is the original harrison radiator it could be either or. My green and white had a 3 row in it and now it has a 4row.
Aaron
Aaron

**kna4977** · 10-08-2006, 12:04 AM

I seem to have the worst luck. At this point I'm fairly certain that the problem is the head gasket on the left side (driver's side). I just hope I haven't done any major damage. How much work is involved in fixing it? Should I have it done or try to tackle it myself? Remember I have terrible luck

Aarons72s · 10-08-2006, 12:15 AM

From the picks that you had on the blazer board I think I would do it myself. Considering from the pictures that I have seen she looks brand new I would pull the motor. If one gasket is leaking there is a good posiability the other is not far behind. If your not comfortable replacing the gaskets your self once you have the motor out you could take it to a shop to due it. Plus you can repaint the motor once you reassemble it to make it look new again. If it was a beater, just fix it in place but since she is pretty much a time capsal I would go all out to do it right. What makes you think it is the head gasket? It is not real hard to do but is just alot of work.
Aaron

10-02-2006, 08:00 PM	#1
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	72 A/c Air Conditioning Troubleshooting I have my factory system installed and charged. The problem is it doesn't blow as cold as I think it should. The compressor runs all the time when the control is set for A/C, not sure if it is supposed to or not. The POA valve and hoses are frosty/icy with the system engaged with a lot of condensation due to engine heat when the system is turned off. The center outlet has colder air than the side vents. The water valve seems to always let water through, except on the rare occasion that I can increase vacuum to it by placing the truck in park and ideling at about 2000 rpm. In drive, under load, it has virtually no vacuum until I let off and coast which allows the air to be somewhat cooler, but not cool enough. The lack of vacuum at the water valve I believe is most likely causing heat to mix with the cool air, but like I said before as vacuum increases, the air does get colder, but still not as cold as it should be. Also, is there a way to increase vacuum on a consistent basis so that there is always enough to close the water valve? I did try to bypass the water valve to see if it the A/C was colder that way, but the truck wants to overheat. Any tips you can give me would be great!

10-02-2006, 08:35 PM	#3
72CSTC5 Account Suspended Join Date: Nov 2004 Location: Deer Park, Tx. Posts: 2,522	Re: 72 A/c Air Conditioning Troubleshooting What refrigerant are you using, r12 or 134a? Did you install all new parts or used? Did you put a new expansion valve in when you installed a/c? New drier? Let us know a little about the system so we can help you diagnose.

10-02-2006, 10:00 PM	#4
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting New expansion valve, drier and lines. R-12 Last edited by kna4977; 10-02-2006 at 10:02 PM.

10-02-2006, 11:41 PM	#7
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,669	Re: 72 A/c Air Conditioning Troubleshooting As for the valve in the engine room on the heater hoses I think they suck! I am planning on going to the junk yard and finding one off of an astro safari. WE have 94 safari that has a really neat water shut off valve. Instead of just blocking off the water it has a bypass tube that just sends the water around the heater core. The van that it is on the air conditioner doesent work but when that valve is closed you dont get any heat from the heater core but in the winter when it opens be prepared to be roasted. Be forewarned you have to go to either a junk yard or the dealer. Not avaliable at part stores. If you want one Go to the junk yard pop the hood on the van and look at the a/c box. It looks similar to our boxes. If you have found the right year there should be a plastic valve that looks like an H with a vacum actuator on top. Hope this helps. Aaron

10-03-2006, 08:59 AM	#9
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting Is frost on the POA valve and associated line normal?

10-02-2006, 08:29 PM	#2
mrein3 Registered User Join Date: Feb 2000 Location: Center City, MN, USA Posts: 3,254	Re: 72 A/c Air Conditioning Troubleshooting LOTS of people take the vacuum controlled valve out and put an in-line, manual one in. That works the best but on a day like today here in MN I had my heat on going to work and the air on going home. The vacuum controlled one is better for that. Do you have the factory vacuum pod that bolts to the ac box on the outside of the firewall? Is it broken? I had a car once that had a leak in that pod. It behaved like you describe. Colder with more vacuum. Almost hot without. A POA system always has the compressor engaged with the AC on. I think if you solve the vacuum issues you'll get cold air from all vents. Did you get your fan speeds all squared away? __________________ '70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN

10-03-2006, 09:26 AM	#10
67chevy2wd Registered User Join Date: Sep 2003 Location: New Salem, ND Posts: 1,558	Re: 72 A/c Air Conditioning Troubleshooting The heater core was never intended to help cool the engine, it is just there to give you heat from the engine. There are a lot of pickup down south that aren't even running a heating system. __________________ 07 Chevy classic LBZ Duramax (a few mods) '67 Chevy 1/2 ton 2wd (in pieces) '69 Chevy 1/2 ton 2wd (on hold) '71 GMC 3/4 ton 4x4 ‘71 GMC 1/2 ton 2wd suburban

10-03-2006, 11:12 AM	#11
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting I increased the idle, and have the vacuum up to where it should be, and the water valve is now functioning properly. The A/C is very cold. However, the problem I have now is that the truck wants to run hot when the water valve is working. Any thoughts on what could be wrong now? Last edited by kna4977; 10-03-2006 at 11:13 AM.

10-04-2006, 12:33 PM	#13
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting I've got the 7 blade fan. I replenished the coolant and replaced the radiator cap today. It is still wanting to run hot, but I don't let it get there. How can I tell what part or parts are bad? It ran fine with the current radiator until a couple of days ago, so I don't think that's the problem. How do you tell if the water pump is bad? What about the thermostat?

10-04-2006, 01:20 PM	#14
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,669	Re: 72 A/c Air Conditioning Troubleshooting Id change the thermostat. Those things are cheap and one year I got a bunch of bad ones. I used to drive a 85 dodge aries and I put about 4 of those thermostats in it before I finally got one that worked. The other 4 just kept sticking and caused it to over heat. This is going to sound like a dumb question but do you have a fan shroud? On my green and white the punk I bought it from threw the fan shroud away and she would overheat. It had the clutch fan on it to with large tank 3 row radiator. Plus he didnt even put a thermostat in it. Well I took the fan shroud and factory? flex fan off my orange and white put them on the green and white and it fixed the problem. But soon after that the tanks started to leak because the radator was rotting out. Went to local parts store and bought a new 4 row radiator I want to say for about $200 but that was also 3 years back. How old is your water pump? Where did it come from? New or rebuilt? You may want to also just change it. There cheap anyway and not that hard to change. Hope this helps. Aaron

10-07-2006, 10:49 PM	#15
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting I replaced the water pump and the thermostat, but still the temp gauge wants to continue to climb higher and higher. How do you know if air is in the system, and how do you get rid of it if it's there? The hoses all look fine, with no kinks, and I have the right amount of coolant in it. What should I do at this point? Do I need a larger radiator? How much soes it cost for a head gasket replacement? Last edited by kna4977; 10-07-2006 at 11:22 PM.

10-07-2006, 11:28 PM	#16
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,669	Re: 72 A/c Air Conditioning Troubleshooting How old is the clutch for the clutch fan? I know when they get old sometimes they do not engage when they get hot. That was one of the problems on my green and white. That is why I only use flex fans. As for getting the air out of the system there is a tool that ataches where the radiator cap goes and they put a vacum on it. Longhorn Man should probably be able to tell you how and where to get it done. As for the radiator due you have a 3 row or 4 row. If it is the original harrison radiator it could be either or. My green and white had a 3 row in it and now it has a 4row. Aaron Aaron

10-08-2006, 12:04 AM	#17
kna4977 Senior Member Join Date: Jul 2006 Location: Midlothian TX Posts: 481	Re: 72 A/c Air Conditioning Troubleshooting I seem to have the worst luck. At this point I'm fairly certain that the problem is the head gasket on the left side (driver's side). I just hope I haven't done any major damage. How much work is involved in fixing it? Should I have it done or try to tackle it myself? Remember I have terrible luck

10-08-2006, 12:15 AM	#18
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,669	Re: 72 A/c Air Conditioning Troubleshooting From the picks that you had on the blazer board I think I would do it myself. Considering from the pictures that I have seen she looks brand new I would pull the motor. If one gasket is leaking there is a good posiability the other is not far behind. If your not comfortable replacing the gaskets your self once you have the motor out you could take it to a shop to due it. Plus you can repaint the motor once you reassemble it to make it look new again. If it was a beater, just fix it in place but since she is pretty much a time capsal I would go all out to do it right. What makes you think it is the head gasket? It is not real hard to do but is just alot of work. Aaron Last edited by Aarons72s; 10-08-2006 at 12:17 AM.



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