A few A/C questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

slamd58 · 03-26-2005, 01:46 AM

Here are the situations.
#1: I just replaced the compressor and converted over to R134. Now it appears that the vacumn actuator/rod that opens/closes the fresh air flap doesn't work. From what I can tell I am missing something but don't know what. The air at the outlet (inside the truck) will only get down to 70 degrees. The only thing I can figure is the heated air and cold air is mixing because the flaps aren't working correctly.... Does anyone have pcitures with the cowl off that shows all the parts? Can I buy a complete unit anywhere?

#2: Vacumn leak at the Heater-A/C control assembly. The leak appears to be coming from inside the unit. I took the assembly out and started the truck, the leak is inside the assembly... Any ideas? New unit?

slamd58 · 03-26-2005, 05:38 PM

ttt

**john** · 03-26-2005, 07:02 PM

I don't know where to get parts for valve, but I put a shutoff in both heater hoses to keep that from happening. Your truck should already have one. Maybe it is not working. John

JimKshortstep4x4 · 03-26-2005, 07:53 PM

Here is a pic of the air valve.

I believe the vacuum switches are still available. They are the same as the 65-66 Impalas and maybe other years.

Jim

incoma · 03-26-2005, 08:01 PM

I have some pictures of the flap assembly if that would be helpful. I just re-installed mine today.

There's also a T connector underneath the A/C box (engine compartment side). That "T" connector connects the flap assembly valve and the heater shutoff valve. Let me know if you need pic's.

Looks like Jim's beaten me to the picture...I don't have a spring on mine...I like that idea though, that way it stay's closed all the way????

slamd58 · 03-27-2005, 02:48 AM

Thanks! Incoma, any pictures you can get me of the flap will help.

JimK is there any chance you can take another shot inside the colw area?

chipflyer · 03-27-2005, 09:26 AM

I bought a new vacuum switch from Ricks Pickup parts to replace my leaky one. I believe it was $15 plus shipping.

JimKshortstep4x4 · 03-27-2005, 09:43 AM

Slammed 58,

Here are a couple of shots of inside the cowl area.

Jim

slamd58 · 03-27-2005, 03:32 PM

Jim - Awesome Shots thanks. the problem is now I am really confused! From what my problem is with cold and hot air combining (increasing air temp out of the vents), then this probably is not my problem. I wonder if I am missing a hot water valve(that turns off the hot water from going to the heater exchange unit in the cab). Man I wish I knew more about how heat/A/C systems work together......

Any thoughts on the vacumn leak behind (attaches to) the heater control assembly..... When I move the fresh air/recirc air lever (middle one) to recir the vacumn leak goes away.... It only happens when the lever is in the middle.... Its noisy and loud and the leak may be causing my Hot/cold air problem....

Keep the help coming.... Sorry for the stupid questions!

JimKshortstep4x4 · 03-27-2005, 08:28 PM

I would suggest checking the vacuum hoses and the vacuum switch. The vacuum switch should have two nimples on it, one for vacuum in and one for control vacuum out. They made some switches with three niples so on your truck if there is a third nipple it should be plugged.

The vacuum hose routing is simple. There is a vacuum line from the engine to the vacuum chamber on the outside heater/ac box. From there the vacuum hose goes straight to the vacuum switch on the control panel.
When the control panel lever is moved vacuum is routed to the inside air door, the outside air door, and the hot water shutoff valve. If you loose vacuum then the doors will not close nor will the water valve shut off.

As a test remove the two vacuum hoses from the vacuum switch and connect together with a 1/8" tube. If the AC then works there is a problem in the vacuum switch.

Good luck, let us know what happens.

Jim

slamd58 · 03-28-2005, 12:27 AM

ttt - need someone with more experience than I to help!!!

1-PU70 · 03-28-2005, 03:31 PM

Thats a really big hole to access the flapper. I dont remember mine being that big. It was a pain to change it. I never saw one with a spring like that. Is that a factory thing? Will the vacume switch still close the flapper with the spring?

demi · 03-28-2005, 06:18 PM

I just got done doing this same thing. On mine there are three nipples. One for the source which goes to the vacuum reservoir on the a/c box; the second line goes to the water valve on the heater hose; the third line goes to a tee where it splits between the outside air flap and the recirculated air flap on the passenger side.

I tested everything with a hand pump to confirm the hose routing and functionality of the system. So far it's fine.

Here's a vacuum diagram.

Hope this helps

demi

incoma · 03-28-2005, 10:03 PM

Sorry slamd58, I'm a bit slow responding to threads. Looks like JimK got you setup with the pics. Here's a few of the vaccum diagrams...

Well, I have to resize the others for them to work.. let me know if you need more.

JimKshortstep4x4 · 03-29-2005, 08:51 AM

Since I am working on a 71 this is the vacuum diagram that I am using, which is a little different.

Jim

slamd58 · 03-29-2005, 07:43 PM

thank you for all your help! I just got off the phone with Old Air Products and they have the vacumn pod that goes on the back of the controller. Mine has 3 places for vacumn lines. I am glad you guys posted the schematics, I wasn't aware of a t for the two fresh air doors. I also ordered a new fresh air door (in the cowl) from them and a new water vavle for grins. Once I get this all done I will let you know how it works.

After talking with old air products they also convinced me to get a new POA valve specifically for R134A freon. Their explanation is the head pressure is higher in R134A systems vs R12 systems. Therefore the POA valve for an R12 system shuts off to early and doesn't allow the system to get cold enough. This valve also changes the system so that it cycles the compressor on/off when head pressure gets to high.... similar to what new systems are like today... I guess GM started doing this in 1973 as well.

I will update once I get all this put on!

slamd58 · 04-10-2005, 02:50 PM

I had a chance to tear apart the heater / AC system yesterday and here is what I found. The 72 blazer has a vacumn pod on the back that has three lines. 1 supply line, and 2 lines that go out. 1 out line goes to the vacumn motors on the door in the cowl and the door on the right side fresh air vent in the kick panel. Got that worked out. Now my problem is the water valve. It is a normally open valve and from what I can tell I need a normally closed valve. Vacumn is supplied when the heater lever is in the hot position and the middle lever is in the "heater position.

Has anyone else ran into this on '72's? All the valves I can find are for 69-72.... They don't specify a specific one just for '72's......

slamd58 · 04-12-2005, 02:03 AM

Anyone have some more experience on heater control valves than I?

JimKshortstep4x4 · 04-13-2005, 08:12 AM

slamd58,

My suggestion would be to hook up your vacuum routing as shown with the two outlet vacuum control.

If you look at the three outlet control as mounted it will have the outlets numbered (1,2,3). Remove the hose from #3 and tee into the hose from outlet #2. Plug #3, (a small line cap will do or use a plugged short hose).
Your AC and heater will work fine with the hoses routed as suggested.

The water flow valve will be off with the AC on with this configuration.

Jim

03-26-2005, 07:53 PM	#4
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Here is a pic of the air valve. I believe the vacuum switches are still available. They are the same as the 65-66 Impalas and maybe other years. Jim Attached Images Last edited by JimKshortstep4x4; 03-26-2005 at 07:58 PM.

03-27-2005, 02:48 AM	#6
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	Thanks! Incoma, any pictures you can get me of the flap will help. JimK is there any chance you can take another shot inside the colw area? __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

03-27-2005, 09:26 AM	#7
chipflyer Registered User Join Date: May 2004 Location: Topeka, Ks Posts: 2,293	I bought a new vacuum switch from Ricks Pickup parts to replace my leaky one. I believe it was $15 plus shipping. __________________ I'm not a pessimist, I'm just optimistic that bad things are going to happen. 1971 Cheyenne Super K10 - tilt, cruise, air, am/fm, tow hooks, factory buckets! 1986 Jeep J10 pickup, - 5.3L Vortec with 4L60e and NP241.

03-27-2005, 09:43 AM	#8
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Slammed 58, Here are a couple of shots of inside the cowl area. Jim Attached Images

03-27-2005, 03:32 PM	#9
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	Jim - Awesome Shots thanks. the problem is now I am really confused! From what my problem is with cold and hot air combining (increasing air temp out of the vents), then this probably is not my problem. I wonder if I am missing a hot water valve(that turns off the hot water from going to the heater exchange unit in the cab). Man I wish I knew more about how heat/A/C systems work together...... Any thoughts on the vacumn leak behind (attaches to) the heater control assembly..... When I move the fresh air/recirc air lever (middle one) to recir the vacumn leak goes away.... It only happens when the lever is in the middle.... Its noisy and loud and the leak may be causing my Hot/cold air problem.... Keep the help coming.... Sorry for the stupid questions! __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

03-26-2005, 01:46 AM	#1
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	A few A/C questions Here are the situations. #1: I just replaced the compressor and converted over to R134. Now it appears that the vacumn actuator/rod that opens/closes the fresh air flap doesn't work. From what I can tell I am missing something but don't know what. The air at the outlet (inside the truck) will only get down to 70 degrees. The only thing I can figure is the heated air and cold air is mixing because the flaps aren't working correctly.... Does anyone have pcitures with the cowl off that shows all the parts? Can I buy a complete unit anywhere? #2: Vacumn leak at the Heater-A/C control assembly. The leak appears to be coming from inside the unit. I took the assembly out and started the truck, the leak is inside the assembly... Any ideas? New unit? __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

03-26-2005, 05:38 PM	#2
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	ttt __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

03-26-2005, 07:02 PM	#3
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	I don't know where to get parts for valve, but I put a shutoff in both heater hoses to keep that from happening. Your truck should already have one. Maybe it is not working. John __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

03-26-2005, 08:01 PM	#5
incoma Registered User Join Date: Mar 2004 Location: Lexington, KY Posts: 865	I have some pictures of the flap assembly if that would be helpful. I just re-installed mine today. There's also a T connector underneath the A/C box (engine compartment side). That "T" connector connects the flap assembly valve and the heater shutoff valve. Let me know if you need pic's. Looks like Jim's beaten me to the picture...I don't have a spring on mine...I like that idea though, that way it stay's closed all the way????

03-27-2005, 08:28 PM	#10
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I would suggest checking the vacuum hoses and the vacuum switch. The vacuum switch should have two nimples on it, one for vacuum in and one for control vacuum out. They made some switches with three niples so on your truck if there is a third nipple it should be plugged. The vacuum hose routing is simple. There is a vacuum line from the engine to the vacuum chamber on the outside heater/ac box. From there the vacuum hose goes straight to the vacuum switch on the control panel. When the control panel lever is moved vacuum is routed to the inside air door, the outside air door, and the hot water shutoff valve. If you loose vacuum then the doors will not close nor will the water valve shut off. As a test remove the two vacuum hoses from the vacuum switch and connect together with a 1/8" tube. If the AC then works there is a problem in the vacuum switch. Good luck, let us know what happens. Jim

03-28-2005, 12:27 AM	#11
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	ttt - need someone with more experience than I to help!!! __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

03-28-2005, 03:31 PM	#12
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	Thats a really big hole to access the flapper. I dont remember mine being that big. It was a pain to change it. I never saw one with a spring like that. Is that a factory thing? Will the vacume switch still close the flapper with the spring? __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

03-28-2005, 06:18 PM	#13
demi Registered User Join Date: Sep 2003 Location: Arizona Posts: 305	I just got done doing this same thing. On mine there are three nipples. One for the source which goes to the vacuum reservoir on the a/c box; the second line goes to the water valve on the heater hose; the third line goes to a tee where it splits between the outside air flap and the recirculated air flap on the passenger side. I tested everything with a hand pump to confirm the hose routing and functionality of the system. So far it's fine. Here's a vacuum diagram. Hope this helps demi

03-28-2005, 10:03 PM	#14
incoma Registered User Join Date: Mar 2004 Location: Lexington, KY Posts: 865	Sorry slamd58, I'm a bit slow responding to threads. Looks like JimK got you setup with the pics. Here's a few of the vaccum diagrams... Well, I have to resize the others for them to work.. let me know if you need more. Attached Images Last edited by incoma; 03-28-2005 at 10:08 PM.

03-29-2005, 08:51 AM	#15
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Since I am working on a 71 this is the vacuum diagram that I am using, which is a little different. Jim Attached Images



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03-29-2005, 07:43 PM	#16
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	thank you for all your help! I just got off the phone with Old Air Products and they have the vacumn pod that goes on the back of the controller. Mine has 3 places for vacumn lines. I am glad you guys posted the schematics, I wasn't aware of a t for the two fresh air doors. I also ordered a new fresh air door (in the cowl) from them and a new water vavle for grins. Once I get this all done I will let you know how it works. After talking with old air products they also convinced me to get a new POA valve specifically for R134A freon. Their explanation is the head pressure is higher in R134A systems vs R12 systems. Therefore the POA valve for an R12 system shuts off to early and doesn't allow the system to get cold enough. This valve also changes the system so that it cycles the compressor on/off when head pressure gets to high.... similar to what new systems are like today... I guess GM started doing this in 1973 as well. I will update once I get all this put on! __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

04-10-2005, 02:50 PM	#17
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	I had a chance to tear apart the heater / AC system yesterday and here is what I found. The 72 blazer has a vacumn pod on the back that has three lines. 1 supply line, and 2 lines that go out. 1 out line goes to the vacumn motors on the door in the cowl and the door on the right side fresh air vent in the kick panel. Got that worked out. Now my problem is the water valve. It is a normally open valve and from what I can tell I need a normally closed valve. Vacumn is supplied when the heater lever is in the hot position and the middle lever is in the "heater position. Has anyone else ran into this on '72's? All the valves I can find are for 69-72.... They don't specify a specific one just for '72's...... __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

04-12-2005, 02:03 AM	#18
slamd58 <- Determination Pays Off Join Date: Dec 2004 Location: Klamath Falls, OR Posts: 77	Anyone have some more experience on heater control valves than I? __________________ 1958 Chevy Pickup 350/350, PS, PB, Tilt, A/C, 4 wheels Discs, 17" Wheels. Full Leather Interior - SOLD 1972 CST Blazer 454/400, A/C, 4" lift, 35's, Double wall top

04-13-2005, 08:12 AM	#19
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	slamd58, My suggestion would be to hook up your vacuum routing as shown with the two outlet vacuum control. If you look at the three outlet control as mounted it will have the outlets numbered (1,2,3). Remove the hose from #3 and tee into the hose from outlet #2. Plug #3, (a small line cap will do or use a plugged short hose). Your AC and heater will work fine with the hoses routed as suggested. The water flow valve will be off with the AC on with this configuration. Jim

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