I finally got my A/C system put together, new adj, orfice, new acumulator, and new o-rings everywhere. Ester Oil added.

My compressor is the one that came with the car('87 GT) and it is the HR-6.

I put 3 12 Ounce cans in using the cheapie Autozone gauge. The compressor kept going on and off. Does it work like that? It would drop to around 25 PSI and kick on and run it to the red in the gauge which is maybe 60 PSI. Then shut off. The pressure would drop back down after maybe 10 seconds and repeat the before sequence. I put 1 can of UV dye refrigerant in so I shut the car off and went around double checking. I just left the gauge on the closed position and when I looked back at it some time later it was at 80 PSI. I didnt try starting my car and running fearing a disaster, and I dont think the compressor would kick on anyways at that pressure.
Any thoughts?

I also read through the search feature here about adjusting the switch on the accumulator to have a lower pressure cutout. Any insight to that?

The air blowing inside was very cold so it was working there.

The pressure at the low side will only be correct while the compressor is running. When it's off, it will read high.
Edit: And yes, it does go on and off. Pressure switches control it. If it stayed on all the time, the evaporator would freeze over.

[This message has been edited by TopNotch (edited 09-03-2009).]

your compressor will cycle on and off charging untill the pressure is reached to complete the circuit and keep it there ,i usually jump the low pressure switch to charge ,if it pulls down to 25 on the low side that is good ,jump the low pressure switch for a minute and tell me what happens ,what does it read then ,do you have a way to test the high side ,

Looks normal to me. The HR-6 compressor is affectionately called a "clutch-slapper", because it constantly cycles on and off. Compressors on newer cars don't do that.

If it cycles 8 times or more in a minute, your charge is low.

quote Originally posted by mid engine monsters: your compressor will cycle on and off charging untill the pressure is reached to complete the circuit and keep it there ,i usually jump the low pressure switch to charge ,if it pulls down to 25 on the low side that is good ,jump the low pressure switch for a minute and tell me what happens ,what does it read then ,do you have a way to test the high side ,

Can you elaborate this statement for me? I don't understand.

I dont have a gauge set for the high side is this recommended? I have a feeling I will be doing more A/C systems in the future. I didnt buy one this time because I was get picky about expenses for this car and I was figuring I wouldn't know what the manifold set was telling me anyways.

quote Originally posted by Blacktree: Looks normal to me. The HR-6 compressor is affectionately called a "clutch-slapper", because it constantly cycles on and off. Compressors on newer cars don't do that.

Or even on some older cars. 87-88 duke Fieros have a V5 compressor -- variable displacement and stays on.

What did you use to evacuate the system before charging it?
With R12 or 134a, a low side pressure around 29 psig is about 32°F, so if the pressure's getting down to 25 psig, it's getting below freezing and tripping the low pressure cutoff. That's normal until you get the system charged fully.

60 psig on the low side is too high. 60 psig is a little over 60°F, so the air coming out wouldn't be very cool at all. It's likely tripping the high pressure cutoff at that point. Since you don't have a gauge on the high pressure side, you can't tell if it's actually getting too high and tripping the cutoff, but the low side should never be 60 psig because it's not cooling effectively at that point. If it were running normally and hitting that pressure, the system would have too much refrigerant in it.

How deep a vacuum did you pull before charging the system?

Ok, what is a new adj? Your low side pressure should drop to about 20 to 21 psi (134a) or 25-27 psi (r-12) before cycling off. It is pretty normal to have approximately 80 psi in the system when the compressor is not running and the pressures have equalized. If you had a high side pressure gauge on the system it would have read approx 80 psi also.

More info needed to accurately answer your question.

what was the outside ambient temperature?
what rpm was your engine running?
was the radiator cooling fan running? (it should be whenever the A/C is selected on)
was your A/C selected to "Max" and full fan?

remember, if the outside temps are approx 85 or above your A/C should not be cycling at idle with the system set to max and full blower. As you rev up the engine above idle rpm, the low side pressures should drop enough to cycle the compressor off.

Charlie


This chart may help (it is for 134a):

[This message has been edited by cptsnoopy (edited 09-03-2009).]

quote Originally posted by cptsnoopy: Ok, what is a new adj? Your low side pressure should drop to about 20 to 21 psi (134a) or 25-27 psi (r-12) before cycling off. It is pretty normal to have approximately 80 psi in the system when the compressor is not running and the pressures have equalized. If you had a high side pressure gauge on the system it would have read approx 80 psi also. More info needed to accurately answer your question. what was the outside ambient temperature? what rpm was your engine running? was the radiator cooling fan running? (it should be whenever the A/C is selected on) was your A/C selected to "Max" and full fan? remember, if the outside temps are approx 85 or above your A/C should not be cycling at idle with the system set to max and full blower. As you rev up the engine above idle rpm, the low side pressures should drop enough to cycle the compressor off. Charlie

to answer the guy above I figured I would grab something to eat and wait until night so the dye would show a little better so I left thinking "first thing I will do is vaccuum out the air" I completely forgot it when I came back. I only have a hand operated vaccuum pump so I could only do around mid-20s vac. I have a very slight leak and couldnt locate it until tonight and I think when I checked it before I left my vac gauge was around 10. So I goofed on that part.

I said 60 but but I can't recall what the gauge says but i think it was more around the 50s before it shut off.

The "adj" is an adjustable orfice tube, supposed to be better I guess. Now I'm also second thinking how my gauge was going. I can't recall if it was climbing while the compressor was engaged running or dropping. The 25 Psi sounds right for it cutting off or on. I read you can adjust that, I would liek to know how BTW, and I thought 80psi wouldnt turn on the compressor because of the cut-out at about 60, though I didn't try it thinking disaster may be looming if I did.

I would think my temp was around 70 in the shop with the garage open, the engine would idle around 1100 or 1000 from its normal smooth 900-950. The radiator fan was on, and it was on max with fan on max speed.

quote Originally posted by 02greens10: I only have a hand operated vaccuum pump so I could only do around mid-20s vac.

There's your problem. You've got air in the system. That's nowhere near a deep enough vacuum to remove the air and moisture from the system.
A hand held vacuum pump can't do the job.

Until you get a good vacuum pulled on the system it will never charge properly.

Here's a link to an HFC-134a Pressure/Temperature Chart.
28psig is right at 32°F. That low and lower will see your evaporator icing up. That 32°F is the temp in the evaporator - not the ambient temp listed in the chart above, or the temp of the air coming out of the vents - that will be higher. But if the evaporator is getting down to freezing, it will start icing up.

I doubt it was freezing sinced it worked constantly the same after I put all the refrigerant in, hopefully the dessicant will get it, but whats the correct vaccum to put on the system?

the amount of time required for evac will be determined by pump size ,system capacity and wether you have all leaks stopped ,if its a small pump let it run for an hour or so ,shut it off and let it sit for an hour or so and see if it holds the vacuum before you continue to charge it

quote Originally posted by 02greens10: I doubt it was freezing sinced it worked constantly the same after I put all the refrigerant in, hopefully the dessicant will get it, but whats the correct vaccum to put on the system?

When I was doing HVAC we had special vacuum pumps designed for use on refrigeration systems. We measured the vacuum in Microns of Water Column, not Inches of Mercury or PSI. For all practical purposes, you need a pure vacuum, or as close as you can get. If atmospheric pressure is 14.7 psia, that means you need to pull a 14.7 psig or so vacuum. If the vacuum pump can't pull a deep enough vacuum, you could let it run forever and it'll never get there.

Your best bet is to take it to an AC shop and have them evacuate it and recharge the system. Don't forget to add the proper amount of oil to the system as well.

How are you using the dessicant, and what type of dessicant are you using?

I was under the impression that the dessicant was in the accumulator that i put in new. I guess I will get some better tools for this job next Spring as by then my system will have evacuated itself. I have a leak on the low-pressure cut-off switch in the compressor. Anyone know where to get a replacement for those? I took another compressor apart and there is an O-ring in there, but I had to basically destory that little switch to get it out because of the corrosion around it. I only see 2 wire versions on the parts websites for replacements.

Yes I did put 10oz of ester oil in my system, because I felt none of the original was left after parts replacement and general pipe cleaning.

It does blow cold air so I'm happy that it does work, and being the first A/C I've ever worked on I'm glad.

I would like to avoid taking it to a shop and paying someone to work on my stuff. I think I would rather make things like this a learning experience and now that I know more I think I will invest a few bucks into some better testing and charging equipment for a DIYer. I have 2 other vehicles that are probably going to need A/C work in the future so it's basically free once I have the proper knowledge and equipment.

[This message has been edited by 02greens10 (edited 09-05-2009).]

Good plan. I understand wanting to do the work yourself, but AC work does require some specific training and tools. It's not hard - you just have to know what to look out for.
Something else you might try is get in touch with your local community college. They'll likely have an HVAC curriculum and you may be able to take your car to them and let them evacuate and charge it, probably for free. When I was studying HVAC service at Wake Tech, we had more students than we had equipment to work on and we welcomed the opportunity to work on people's stuff. I redid the AC on my '69 Firebird during the class, and a few other guys brough in old refrigerators and window AC units to repair.

A good pair of manifold gauges and a good vacuum pump and you can do most work. A quality HVAC vacuum pump will be expensive, but lots of people "get by ok" with regular pumps. They'll tell you they've used it for years without problems. But how many times have you had a shop "fix" your AC only to have it need "fixing" again next season?

With the right equipment you can fix it properly the first time and it will STAY fixed.

I would second getting a decent set of guages. you will need different sets for r12 and 134, best to keep them seperate and not just swap hoses. You can often find em at garage sales.
As for your leaking switch, well, that;s a rough one, I had the same issue, but it was the O ring. the switch is held in wiht a snap ring, if that comes out you can carefully work out the switch, just be sure the system is empty.
For evacuating, old trick is to locate a small old refidge that is in the trash, and cut out the compressor. locate the suction side and solder on a fitting and use that, it should pull down to mid to high 20's depending on the state of the compressor. (my guages read vacuum) I go for -28, valve off the system, let it sit for 30 minutes, and pull it back down again and recharge. If you see a rapid climb with the vacum with pump off, you have a raging leak. if it can still hold aorund 18-20 after a half hour it is fine. a common mistake is believe that even then the system is leak free, but unfortunately, that is NOT the case, as it is not a vacuum system, but a pressurized system. if you really want to verify system is intact, pressurize it with an inert gas like nitrogen, and then soap it up with kids bubble blowing liquid on the hoses and joints. then re vacuum the system and charge.

Would the Harbor Freight vacuum pumps work ok? And how about the manifold gauges? Any recommendations for under $80? I may try to get this done this year even. I'm so close, and if it weren't for that switch it would be completely leak free. I think I will just let the 134 leak out and maybe try to fix it. It may take awhile.

I hope it comes out, but it's a tight spot and not breaking that low pressure switch is gonna be fun.

quote Originally posted by 02greens10: Would the Harbor Freight vacuum pumps work ok?

Yes ... if you mean their motorized vacuum pumps, and not their cheap boxes that use compressed-air through a venturi to produce a vacuum. I have one (motorized), as well as one of their R134a manifold sets. If you wait for them to go on sale (prices vary widely from week to week at HF), you can buy a manifold set for less than $40, and a motorized vacuum pump suitable for occasional automotive or small appliance work for about $60.

FWIW, the HF vacuum pump can also be used for vacuum bagging if you occasionally do composite (e.g. fiberglass) work.

[This message has been edited by Marvin McInnis (edited 09-06-2009).]

Adjusting the low side pressure cut off switch is done via
a screw that is located under the connector. The switch is
located on the driver's side of the accumulator. Take the
connector off and you will see the screw. The adjustment is
counter-clockwise=lower pressure (approx 2psi for each 1/8 turn).
If you think your compressor is cycling too fast, and everything
else is ok (ie charging, no leaks, etc), then you can effect
the cycling by adjusting the low side switch. The trade off is
keeping the air blowing cold.

quote Originally posted by Marvin McInnis: Yes ... if you mean their motorized vacuum pumps, and not their cheap boxes that use compressed-air through a venturi to produce a vacuum. I have one (motorized), as well as one of their R134a manifold sets. If you wait for them to go on sale (prices vary widely from week to week at HF), you can buy a manifold set for less than $40, and a motorized vacuum pump suitable for occasional automotive or small appliance work for about $60. FWIW, the HF vacuum pump can also be used for vacuum bagging if you occasionally do composite (e.g. fiberglass) work.

X2. I have both the R134a pressure gauge set and the electric motor type vacuum pump. Both work great so far although both plastic knobs on the gauge set have broken off. It appears that a standard outside faucet knob should work as a replacement.

Go to a used appliance store & ask for a compressor from a junk refrigerator. You can find instructions on the internet on how to make it into a vac.

I got a compressor for free & had to solder on a fitting that cost about a dollar.

If you are interested in a low cost refrigerant, <$1/lb, PM me.

quote Originally posted by 30+mpg: Go to a used appliance store & ask for a compressor from a junk refrigerator. You can find instructions on the internet on how to make it into a vac. I got a compressor for free & had to solder on a fitting that cost about a dollar. If you are interested in a low cost refrigerant, <$1/lb, PM me.

http://www.dream-models.com/eco/vacuumpump.html