R12 Air Conditioning questions

[ford man]

A friend, who is a commercial AC technician, is helping me get the '85's AC going again. We're using r12 freon. So far all we have done is replace the schrader valves and caps. He partially charged it and checked for leaks with a digital vacuum gauge and he said the micron reading was very good. Over 480 or something like that. We also checked for leaks with a leak detector under the hood and inside the car and there weren't any. So I guess I'm good to go! But I have some questions to relay to him because he dosen't work on cars normally...

1. What should the low side and high side readings be for r12 on the gauges?

2. He thinks he fully charged it but the compressor still cycles every 5-10 seconds. Should we adjust the pressure switch to a certain pressure?

3. When you check your gauge readings is that at a certain rpm or just at idle?

4. He wants to add some oil to the system... Is that 525 mineral oil for r12? And is the total oil charge 13oz?

5. Is there anything that we are forgetting or should look at?

We did vacuum it down with a electric vacuum pump and it held good vacuum.

Thanks for your replies guys!

[Lincolnmania]

google r12 ac pressure chart........it depends on ambient temp

did he use a charge scale or just charge it till the compressor came on?

yes use mineral oil.......theres gotta be some in there, i usually add 2-4 ounces when doing a recharge

there is an adjustment on the pressure switch

[BigT]

R-12? Are they still selling that? How much is a can now-a-days? $1,000 a pint? I remember the EPAput a ban on it and the price rose crazy. So I converted to R-134a about 10 years ago.

[GoodSamaritan]

I've still got a couple of cans of r12 and a smidge in the bottom of a cylinder.
Btw has anyone else noticed how %#@! expensive r134 is getting?

[86VickyLX]

Replace the accumulator drier, and the orifice tube if you haven't already. The A/C system takes 3.25lbs of R12 refrigerant. It shouldn't cycle every 5 seconds, however, it really hasn't been warm out. But looking at a set of manifold gauges should tell you what's going on.
Low side should be around 26psi to low 30s. If it goes lower than that, then it's not charged fully. The switch shuts off at a certain PSI to keep the compressor from cycling with a low freon charge. I should know what PSI that is, because I had a disagreement with one of the other members on here about the switch's operation. The high side, should be into the triple digits, but it shouldn't be ridiculously high. It should be substantially higher than the low side, and with the AC not on, the pressures should equalize if allowed to sit long enough.

[gadget73]

There is indeed a pressure vs temperature chart. There is also an expected amount of compressor cycling based on temperature. Its in the shop manual but the R12 pressure chart can be found online. Just be aware that some of them don't use ambient temp, but use superheat an supercool temps. Superheat is the hot discharge from the compressor, supercool is immediately after the orifice tube at the bottom of the evaporator. Truth be told, if dude is an AC tech, he ought to know this

[ford man]

google r12 ac pressure chart........it depends on ambient temp

did he use a charge scale or just charge it till the compressor came on?

yes use mineral oil.......theres gotta be some in there, i usually add 2-4 ounces when doing a recharge

there is an adjustment on the pressure switch

Ok thanks. I'll check it out.

He had manifold gauges hooked up to the high and low and charged it until it looked right to him I think.

I bought a quart of 525 and he has a oil injector to put it in.

He asked if it was a high or low safety on the switch. I told him I think it shuts off the compressor when the pressure gets too low?

[ford man]

Replace the accumulator drier, and the orifice tube if you haven't already. The A/C system takes 3.25lbs of R12 refrigerant. It shouldn't cycle every 5 seconds, however, it really hasn't been warm out. But looking at a set of manifold gauges should tell you what's going on.
Low side should be around 26psi to low 30s. If it goes lower than that, then it's not charged fully. The switch shuts off at a certain PSI to keep the compressor from cycling with a low freon charge. I should know what PSI that is, because I had a disagreement with one of the other members on here about the switch's operation. The high side, should be into the triple digits, but it shouldn't be ridiculously high. It should be substantially higher than the low side, and with the AC not on, the pressures should equalize if allowed to sit long enough.

Thanks.

What pressure should the compressor switch off? I thought at idle it would be on most of the time?

If I replace the accumulator drier and orifice tube will it help it get colder? He said that was a good idea and has a recovery machine to discharge so I can replace that stuff. Just wondering if those parts are maintenance or a restriction or what?

[ford man]

There is indeed a pressure vs temperature chart. There is also an expected amount of compressor cycling based on temperature. Its in the shop manual but the R12 pressure chart can be found online. Just be aware that some of them don't use ambient temp, but use superheat an supercool temps. Superheat is the hot discharge from the compressor, supercool is immediately after the orifice tube at the bottom of the evaporator. Truth be told, if dude is an AC tech, he ought to know this

He normally works on 100 ton chillers that cool large sound stages or warehouses. He is real knowledgeable about that stuff. He is also helping me out for free including all the r12 so I can't complain.

[86VickyLX]

Thanks.

What pressure should the compressor switch off? I thought at idle it would be on most of the time?

If I replace the accumulator drier and orifice tube will it help it get colder? He said that was a good idea and has a recovery machine to discharge so I can replace that stuff. Just wondering if those parts are maintenance or a restriction or what?

Somewhere around 18psi or so. The cut off switch is a low pressure switch. We do not use a high pressure shut off switch, we only have a high pressure diverter valve. Unless you're in California, then I think they have a high pressure switch as well.
if you replace the drier, it will help remove moisture better. Think of the drier as a diaper, it sucks up all moisture that it finds. If it's already saturated from moist air (exposed when the system was opened), then it can't work like it's supposed to. The orifice tube is what makes the AC so cold. It's also a filter. So do go and replace it. And use the proper tool. Save yourself a headache.

[gadget73]

Its actually about 25 psi for R12. Out at 25, in at 40 or 45, forget which.

[ford man]

I bought an accumulator from Rock Auto. My choices were factory or dealer installed air conditioning. I bought the one that is for factory installed air conditioning. And this thing came^^^. Looks just like the picture. The one on the car looks nothing like this! So.... also autozone and Oreilly's have the same looking accumulator on there websites. What's the deal? Can I make this thing work? Have you guys had experience with this?

[sly]

what does yours look like (got pics)? Maybe we can sort the issue.

[ford man]

I borrowed a picture from 87gtvic's readers rides thread... His accumulator looks exactly like mine. I believe that's the original style. The second picture is the contraption that came from Rock Auto that is supposed to be for factory installed air conditioning. Can I make this thing work?

[sly]

yeah... you need the panther style one. Apparently these computer databases are all wrong on that part for the crown victoria (using the fox body LTD parts).

I tend to think the former since my 82 Mark has the same setup as well.

Autozone part number: 33168 (Four Seasons)
FOUR SEASONS Part # 33201
SPECTRA PREMIUM Part # 0233168

You need the grand marquis one. I'd send it back and have them fix their database.