Need help with charging A/C system

[kevken1959]

Hi all. I have limited knowledge of the A/C system. I'm working on a 72 system. I replaced the expansion valve, compressor, dryer, and condenser. I blew through the evaporator with compressed air but did not flush it. I did this about three months ago but I can't remember if the air came through totally freely. I also blew through the hoses. The system has a quick disconnect valve that is original. I did not take it apart but I did replace the o ring. I took the car to Express Oil and they evacuated the system but they were unable to get R131A Freon into the system. They said only about 1/3 of the Freon went in. There was no cooling. The High side pressure was 200 and Low side was 165. What are the possible causes of this problem, and what should be my next step? I'm afraid the evaporator may have a partial blockage or that the quick disconnect valve may be stuck. I'm fixing to remove the expansion valve (which is a major pain in the ass), and trying to flush the evaporator. I'm also considering taking the quick disconnect valve apart and cleaning it. Also, I think I have hoses from a 73 that don't have the disconnect valve that I can swap out to eliminate that problem. Thanks. Kevin.

 

[Sheriff41]

What was the ambient temperature? Was the compressor clutch engaged when you took this reading? Did the low side pressure drop when the clutch would cycle?

 

[kevken1959]

Hi Chuck. I'd say it was about 78 to 80 degrees inside the shop with the doors open and the fans running. Again, I was at an Express Oil change. The guy working on the car was young, maybe in his 30s, and marginally familiar with old cars. He ran the machine for about 15 minutes after the system held a vacuum then he started the car and revved the engine to 2000 rpm while the A/C ran with the clutch on. I took the picture of the gauges after the engine was shut off, so I can't say what the gauges showed with the car running, however I think those were the same readings. I do not think the low side pressure dropped the way it was supposed to. Sorry, but I just don't know how to read the gauges as I have always gotten someone else to charge my A/C systems. A mechanic friend of mine had told me that he had occasions where it was very hard to get a system to take a charge and that he sometimes had to do it when it was very hot outside. Another friend told me that there must be a blockage in the system somewhere but I haven't a clue as to where to look . Thanks. Kevin.

 

[Sheriff41]

Yes, there are a lot of things in the AC system that can cause problems and an experienced tech is invaluable. However, there is a lot we can learn by checking some online references on reading the AC gauges. Here's one that may offer some insights: https://ricksfreeautorepairadvice.com/abnormal-ac-pressure-gauge-readings-and-the-causes/

 

[Steve McMahan]

I think if it was me, I would find an ASE Certified mechanic who specialize in AC systems. I’m sure you’ll get lots of ideas here, but without the correct tools/instruments, you’ll not be able to act on them. Just my 2 cents

 

[kevken1959]

I think if it was me, I would find an ASE Certified mechanic who specialize in AC systems. I’m sure you’ll get lots of ideas here, but without the correct tools/instruments, you’ll not be able to act on them. Just my 2 cents

Thanks Steve!

 

[kevken1959]

Does anyone know the purpose of the plastic cap on top of the expansion valve, and is it important?

 

[Steve McMahan]

It’s not needed to function. I suspect it was installed to prevent damage during shipping.

Edit: protection while in the box.

 

[kevken1959]

It’s not needed to function. I suspect it was installed to prevent damage during shipping.

Edit: protection while in the box.

Thanks!

 

[Hemikiller]

Was he aware how to open the service valves on the compressor? Seeing that the protective caps are still in place, I'll assume he did not. If he didn't open the valves to the service position, he only put a vacuum on the lines for the machine and nothing else.

 

[kevken1959]

Boy, that's a good point. That's why I posted the pictures. He was from a different store so I will try to track him down next week and ask. Thanks!

 

[cv_72mustang]

I'd find somebody else! I'm no expert but I've done few in my days, didn't he look at the gauges to see what the hell was happening.

 

[Bill Kanode]

Was he aware how to open the service valves on the compressor? Seeing that the protective caps are still in place, I'll assume he did not. If he didn't open the valves to the service position, he only put a vacuum on the lines for the machine and nothing else.


View attachment 89533




View attachment 89532

Since the technician didn't open the service valves he must be a real family genius. Go back to that shop and have your money returned.

 

[Horsin' Around]

Hi all. I have limited knowledge of the A/C system. I'm working on a 72 system. I replaced the expansion valve, compressor, dryer, and condenser. I blew through the evaporator with compressed air but did not flush it. I did this about three months ago but I can't remember if the air came through totally freely. I also blew through the hoses. The system has a quick disconnect valve that is original. I did not take it apart but I did replace the o ring. I took the car to Express Oil and they evacuated the system but they were unable to get R131A Freon into the system. They said only about 1/3 of the Freon went in. There was no cooling. The High side pressure was 200 and Low side was 165. What are the possible causes of this problem, and what should be my next step? I'm afraid the evaporator may have a partial blockage or that the quick disconnect valve may be stuck. I'm fixing to remove the expansion valve (which is a major pain in the ass), and trying to flush the evaporator. I'm also considering taking the quick disconnect valve apart and cleaning it. Also, I think I have hoses from a 73 that don't have the disconnect valve that I can swap out to eliminate that problem. Thanks. Kevin.

Is R131A some sort of replacement to use in R12 systems?

 

[kevken1959]

Is R131A some sort of replacement to use in R12 systems?

Sorry. R134a, lol.

 

[cjstaci]

134a is the current replacement but you have to change the hose connections. You can still use r12 but it’s harder to find and more expensive. The oils are different too and are not compatible with each other. Also, converting to 134a, the amount of refrigerant charge is different. There’s a conversion chart for that.

 

[kevken1959]

So I took the system apart again and cleaned the quick disconnect valve and flushed the evaporator and replaced the expansion valve again. I opened the service valves 1/2 way so all the shop has to do is evacuate the system and charge it. The problem is that the system just will not take up the Freon and fill. That is assuming that the mechanic did open the service valves correctly and just put the caps back on to prevent losing them when he was charging the system. He said it took about 1/2 the Freon so I find it hard to believe he had the valves completely closed during the charging. I spoke with a good mechanic who told me he often has this problem when trying to charge an old system like this when the ambient temperature outside is cool. I would suspect this would have something to do with the expansion valve not opening during the charging process. If that is the case, has anyone tried hitting the expansion valve with a heat gun during the charging process? Does anyone think this might be a good idea? Thanks. Kevin.

 

[cjstaci]

When he was charging the system, did the compressor kick in? If not, he may have to jump the pressure switch. Make sure the proper amount of oil is in the system and that the system is evacuated and no leaks.
I’m not an expert at anything, just enough knowledge to be dangerous, lol. There’s a new member in the forum who mentioned he did a lot of AC work at Ford. Maybe he can give you some expert advice.

 

[kevken1959]

When he was charging the system, did the compressor kick in? If not, he may have to jump the pressure switch. Make sure the proper amount of oil is in the system and that the system is evacuated and no leaks.
I’m not an expert at anything, just enough knowledge to be dangerous, lol. There’s a new member in the forum who mentioned he did a lot of AC work at Ford. Maybe he can give you some expert advice.

Thanks. Yes. I saw the compressor running as he was trying to charge it. On the oil, that is a guess. I installed the compressor. Strangely, the instructions said to drain all the oil out of it before installation, which I did. I think he said he installed about 6 oz of PAG oil. When I got the car home, I put a home made dip stick through the fill hole at the top of the compressor and it has about an inch of oil in the bottom of it. I have seen this done as a way of checking the oil level, but I'm not sure what it should be. Does anyone here know? Also, I can tell the oil has flouroscene dye in it. Thanks. Kevin.

 

[cjstaci]

The shop manual shows 1-1/8”. It says to run the engine and ac for 10 minutes so the oil returns to the compressor. Then isolate the compressor, make sure the compressor shaft keyway is facing towards the compressor head and when inserting the dip stick make sure it bottoms against the lower side of the crankcase and not the boss. Afterwards, you need to evacuate the compressor and recharge it.
The 1971 shop manual says the york compressor takes 10 oz of oil and a full charge of r12 is 1.75 lbs. you will need to refer to a conversion chart for 134a. It will take less.
Also, as previously mentioned, if the ambient temp is cool it may not take the full charge but you can heat the refrigerant. The shop should have a tank heater if it’s needed.