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A/C Not working, where do I start?


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On my newly aquired Mach 1 the A/C is not working, A/C is one of the reasons I bought it.  Where do I start?  Do I have a shop check the compressor/charge first?  Also want to find out if it has been changed over from R12.  I see a boatload of wires, vacuum lines, etc. under the dash, perhaps something is not getting switched

 or turned on?  I know there is current going to the compressor by testing the line but that is all I know.  Should I replace the vacuum canister under the dash?

 

thanks

 

https://www.originalair.com/71-73-mustang-ac-vacuum-canister

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See if you can locate the Ford manual on line that you can download. If it has been switched to 134 there should be different fill valves screwed on the originals.

If it has not been done you have to take all the hoses off, put in the green O-rings that are made for the 134. There are like three that get missed on the compressor one for the vent and the two drain plugs. You will have to invest in some tools also but Harbor Freight has them at a reasonable cost that is less than one trip to a garage. Vacuum pump and gauges for charging.

I went through my vert system and converted it to a highly refined propane made by Dura Cool in Canada. It only takes one can to recharge a vacuumed system. 

Once you get everything cleaned. You probably will have to take the box out and take the coil in the box to someone that has a cleaner for them. Change the heater core while out. 

I used gun cleaning brushes to clean inside the hoses, metal parts next to the fittings. You will need to get a new dryer filter up front any mustang supply has them. 

When all back together you pull a vacuum on the system and then let it sit an hour and if it does not loose the vacuum you have a good closed system. If it leaks you have to find the source. That is difficult some times. If it is good you put the new lubricant in the compressor and then vacuum again and put your refrigerant in. Google Dura Cool it does work way better than 134 or R12. 

One other thing you should replace the shrade valves at your gauge hook ups can get o-rings and valves at local auto supply. You can order the Dura Cool on line.

There are several threads on here if you do a search.

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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I would make sure the compressor clutch is engaging and spinning the compressor before anything else. Make sure the blower is blowing air. The flapper doors in the heater/A.C. box are controlled by vacuum motors via a vacuum switch on the back of the heater/A.C. control panel. The vacuum switch is somewhat fragile and embrittled by time and yanking on the vacuum lines will likely break something. The blower and compressor clutch are controlled by electro-mechanical switches. You'll need to have someone with gauges, or buy your own, check the pressures in the system. As David said, if yours has been converted to R-134a it will have different connections for testing and recharging.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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jscottOn my newly aquired Mach 1 the A/C is not working, A/C is one of the reasons I bought it.  Where do I start?  Do I have a shop check the compressor/charge first?  Also want to find out if it has been changed over from R12.  I see a boatload of wires, vacuum lines, etc. under the dash, perhaps something is not getting switched

 or turned on?  I know there is current going to the compressor by testing the line but that is all I know.  Should I replace the vacuum canister under the dash?

 

thanks

 

https://www.originalair.com/71-73-mustang-ac-vacuum-canister

 

 

if you need any compressor parts or clutch Assyrian parts let me know.  I want to get rid of some spares.

 

kcmash

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The vacuum canister should be under the hood. As long as it's not rusted out and holds vacuum there's no reason the replace it. You'll need to make sure the check valve in it is functional, too.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Check valve in the canister? Or on a vacuum line from the caknister?

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Check valve in the canister?  Or on a vacuum line from the caknister?

 

There are two rubber tubes connected to the outlets on top of the black canister.  One has the vacuum signal coming in from the engine source, the other is the outlet to A / C functions via the rubber tube going through the firewall..  Mine was hooked up backwards and I copied the mistake on replacement.  Sorted it by starting the engine, connected the engine side line but no reaction from the other tube.  Swapped them around and, presto, slight noise as the check valve did its job then I could feel the pull of vacuum on the second tube.  These check valves can fail over the years and I doubt you can pull it apart to replace.  Probably have to get another canister but check it first.   

Have fun.

PKJ

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OK, take it back a notch and do this systematically. You can't just throw parts at a problem, if there is no problem.

 

First thing, is I HIGHLY recommend you invest in the Ford shop manual set from Ohio Mustang, NPD or any other vendor. I cannot stress this enough.

 

https://www.npdlink.com/product/shop-manual-1972-ford-mercury-car-5-volume/138045?backurl=search%2Fproducts%3Fsearch_terms%3Dmanual%252Bbook%26top_parent%3D200001%26year%3D1972&year=1972

 

 

1) you state you have 12V at the compressor wire. If that's true, then the compressor switch under the dash is being activated by the control lever. This sometimes comes out of adjustment. I'm also going to assume you have a belt on the compressor and it's turning the flywheel. 

 

2) if you have 12V at the compressor, does it pull in the clutch? If it does, then go to next step. If not, with the car off, use a jumper and apply 12V to the wire coming from the clutch. If it does not pull in with an audible "clack", you need to start there. Could be a burned out clutch coil, or the clutch could be frozen on the shaft. 

 

3) if the clutch does pull in, with the engine running, does it spin? It's pretty easy to see this happen.  If it pulls in, but does not spin, then you need to investigate why. It could be the compressor is locked up (can you turn the center of the clutch by hand?) and,or the friction material is cooked off.

 

 

That should give you something to work with - post back when you do the checks above.

 

 

 

72AC.jpg

 

72accircuit.jpg

 

 

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I do have a shop manual and I just came in from looking at it. I did pull the wire apart (there is a male/female connection on the wire near the compressor, while the car was running and I did hear that "clack" you mentioned but did not notice any change to idle or other indication that there is a bigger load on the engine, not sure if I should perhaps my past experiences are confused in that respect. There is vacuum going into the canister suction on the out port that goes to the dash. Belt attached and seems to run fine. I do have a appointment at an A/C shop on Monday for them to do their thing as I an not that mechanically inclined. there is one bolt missing from the top of the compressor but I cannot imagine that having any impact on anything. I do have heat, defrost, etc. so switch in that respect is working. Want to get this done so I can start to tear into the interior along with other items on the car. Wife said to by a project to keep me busy........

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I do have a shop manual and I just came in from looking at it.  I did pull the wire apart (there is a male/female connection on the wire near the compressor, while the car was running and I did hear that "clack" you mentioned but did not notice any change to idle or other indication that there is a bigger load on the engine, not sure if I should perhaps my past experiences are confused in that respect. There is vacuum going into the canister suction on the out port that goes to the dash.  Belt attached and seems to run fine.  I do have a appointment at an A/C shop on Monday for them to do their thing as I an not that mechanically inclined.  there is one bolt missing from the top of the compressor but I cannot imagine that having any impact on anything.  I do have heat, defrost, etc. so switch in that respect is working.  Want to get this done so I can start to tear into the interior along with other items on the car.  Wife said to by a project to keep me busy........

 

OK, that's great. You have a functioning clutch, vacuum to the A/C system and from your description, the vacuum motors are functioning properly and changing the outlet air from defrost, dash ducts and floor. If you had no vacuum in the system, the default setting is defrost. 

 

One other thing you can check is the function of the water shut off valve. It's spliced into one of the heater hoses and can fail due to rust, or the vacuum diaphragm goes bad.To avoid paying someone to do this, I would pull the valve from the heater hose and make sure the flap inside is present and not rusted off. Check the condition of the vacuum motor on the valve by rotating the valve arm to the limit of it's travel and cap the vacuum port with your finger. When you release the arm, it should stay in place, which indicates a healthy diaphragm. If it slowly or immediately returns, then you need a new valve. Once you've established it moves and holds vacuum, reinstall and move the control to AC and the temperature lever to the cool range, it should be supplied vacuum and close, restricting hot water flow to the heater core. If it doesn't close, it could be the water valve vacuum switch is out of adjustment, or the temp control cable (which moves the blend door arm, which activates the switch) needs adjustment. There's a really good diagram in the shop manual of the A/C box and components.

 

That's really about it as far as checks you can do without a set of gauges. Hopefully it just needs a vacuum and recharge.

 

 

You'll thank yourself a million times for investing in those manuals, they really are a lifesaver with these cars.

 

 

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OK, that's great. You have a functioning clutch, vacuum to the A/C system and from your description, the vacuum motors are functioning properly and changing the outlet air from defrost, dash ducts and floor. If you had no vacuum in the system, the default setting is defrost. 

 

One other thing you can check is the function of the water shut off valve. It's spliced into one of the heater hoses and can fail due to rust, or the vacuum diaphragm goes bad.To avoid paying someone to do this, I would pull the valve from the heater hose and make sure the flap inside is present and not rusted off. Check the condition of the vacuum motor on the valve by rotating the valve arm to the limit of it's travel and cap the vacuum port with your finger. When you release the arm, it should stay in place, which indicates a healthy diaphragm. If it slowly or immediately returns, then you need a new valve. Once you've established it moves and holds vacuum, reinstall and move the control to AC and the temperature lever to the cool range, it should be supplied vacuum and close, restricting hot water flow to the heater core. If it doesn't close, it could be the water valve vacuum switch is out of adjustment, or the temp control cable (which moves the blend door arm, which activates the switch) needs adjustment. There's a really good diagram in the shop manual of the A/C box and components. That's really about it as far as checks you can do without a set of gauges. Hopefully it just needs a vacuum and recharge.

 

 

You'll thank yourself a million times for investing in those manuals, they really are a lifesaver with these cars.

 

 

I did all of the above and the valve seems to be working as it should. However the temp control lever, when pushed all the way to the left (cool) does not stay there but pulls back about 1/2".

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I take it you have no recourse as far as getting the AC working. You said AC was one of the reasons you bought the car, but was it represented to you as functioning or did they tell you it wasn't working and only needed a recharge? (the usual reason) Was this a private sale or classic car dealer type of place? It sounds like you are on the right track regardless. As long as no major components are missing you should be able to get it working with a bit of troubleshooting and cash.

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Yep, just needed a re-charge, private seller. And when buying in the early am in 3 degree weather it was not the best time to try it out lol. Just need to figure out where to get the new hoses now that one has a pin hole leak and I am good to go.

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  • 1 month later...

In the shop manual, in the section regarding the A/C system, is a trouble shooting "flow chart" for the controls. It starts by warming up the engine and checking for proper manifold vacuum, if within limits, you go next to the vacuum reservoir cannister and check for proper operation, and so on, and so on. Inside the car, under the dash, are various color-coded vacuum hoses. The manual continues, walking you through select this mode, check here, switch to this position, check there. When you do it this way, you will eliminate any control issues, leaving any issues to be in the system components somewhere. Done this way FIRST, any doubts as to the control of the system is answered. I think I would have the shop pull a vacuum on the R-12/ R-134 system next to find any possible leaks BEFORE I would try to charge it up . Personally, I still run R-12 , despite what Greenpeace says it does to the ionosphere, R-12 is , and has always been, used in aviation for it's boiling point, and it is a superior refridgerant to R-134. It has been hard to find for automotive enthusiasts, and expensive when you do, but I know when I worked doing aircraft maintenance, we used it, and had lots of it. Secondly, I like to keep my car as a restored driver, so I keep the R-12 system and original style compressor/condenser/evaporator/and hoses.

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