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A/C Compressor Short Cycling-Odd problem NOT low refridgerant issue
First off the amount of misinformation on this Forum is mind boggling. Second I'm looking for potential additional and intelligent insight to this issue not guessing or BS.
Ok, that being said. A couple years back the car developed a leak in the condenser which let all the R12 out. I replaced the condenser, accumulator, installed new conversion valves to R134a fittings, put in correct amount of oil per GM TSB on retrofits, and charged the system. Worked pretty good for a month or so. Then it was throwing a DTC 09 - Low Freon code. Short cycling....at anything other than idle. I ran the A/C with manifold gauges on it and the pressure cycling switch was kicking the compressor in and out about where it should be but like I said before was short cycling. FSM says about clogged orifice tube, so I evacuated the system and pulled the tube. Cleaned it up a bit and reinstalled, not much on it really. The evacuation pulled a bunch of oil out maybe 2 oz? Recharged and the system ran ok again for a month or so. That got me thru the season I needed it, well guess what same DTC and its not working again...
Evacuated the system today (full charge 1.75lbs of R134a-never has had leaks). Cleaned off OT, and put it all back together and it threw the DTC in short order. Didn't get much oil out with evacuation this time. I don't my gauges at home to double check the pressures but given the ice forming on the low side tubing I'm going to say they are too low. I felt ALL hoses/pipes for ANY temperature drops (clogs/bends) that are NOT from the OT. None where found.
I can only see THREE possibilities to this:
1.OT has a clog I cannot visibly detect.
2. Some sort of physical clog in the evaporator. Lines cold going in (after OT) and out. Might be colder on outlet than inlet but its hard to tell as the OT is still causing the refrigerant to expand as it goes into the evaporator so I don't want to read into it.
3.Cycling switch is bad? I found OLD threads talking about adjustments that supposedly applied to a 93 but they are full of it. The cycling switch is the same design as 94-96 as far as I can tell.
Keep in mind when I first did the condenser, etc...it worked just fine for about a month. I'm considering shot gunning a OT at it and maybe a cycling switch, but I'm more leaning towards the OT more so than the cycling switch.
Something really odd happened as I was pulling a vacuum. It was just getting into a deep vacuum and I had a pop and sucking noise, the vacuum readings went more towards weak vacuum like I had an air pocket? Doesn't make any sense, only connected the valves once and both sides where reading about same pressure before I evacuated it so.....IDK.
If anyone has any additional insight it is welcome.
Something really odd happened as I was pulling a vacuum. It was just getting into a deep vacuum and I had a pop and sucking noise, the vacuum readings went more towards weak vacuum like I had an air pocket? Doesn't make any sense, only connected the valves once and both sides where reading about same pressure before I evacuated it so.....IDK.
If anyone has any additional insight it is welcome.[/QUOTE]
Is it the original compressor? My first thought on this is the compressor front seal sucking in some air while pulling a vacuum. Air in the system can cause abnormal pressure readings and poor performance. Denso seal kits are cheap and easy to install with no special tools. I also replace the orifice tune any time the system is open.
The first thing I always do is, after setting overnight and everything at ambient temperature, check the static pressure. both sides should be equal and slightly above ambient temperature. If good, run the a/c and check the discharge temperature and high and low pressures. A restriction will cause abnormal pressure readings. Good luck with your project. I fought my hvac system for many years and spent a fortune but now it works great. It is frustrating to have to discharge and recharge a system.
93 Rubie I just finished an A/C conversion of my 15 year non working system on my OLDS. It takes about 8oz Easter oil and 36 oz R134.
Almost the same as my 85 Corvette.
But you have to replace the receiver /dryer (whenever the system is opened) to prevent freezing. Plus I would say replace the pressure cycle switch, high pressure cutoff, and low pressure switch for sure.
They could be bad and you will never be able to troubleshoot correctly. I am not saying they are bad, just saying you will never be able to troubleshoot.
Good Luck!
One other thing I don't think there is any adjustment (for us to do) on the cycle switch, just get the right one and it will be adjusted.
I had a warning with mine about that.
Yes here are the pressures for the 85 Corvette.
And here are the pressures for the 90 OLDS 88. Little bit newer system. Little cooler outside.
Here is the chart I use.
I'm curious what pressure it is kicking it out at. Yes I've seen the switches be flakey and cause this, I've also seen the r12 switch used with 134 and it will do... weird things sometimes. Others itll be fine. The kick out pressures should be close enough
When you were checking the pressure, were the readings steady or fluttering? Do you have vent temperatures as well?
The early switches are adjustable, I have seen that switch on the 90s vettes but not sure if it was factory or replaced with it. You should have the later non adjustable one.
When your AC Kicks Off, The Compressor Clutch should be Disengaged, the primary purpose of these sensors, aka switches. The Low & High Pressure switches do Fail and often intermittent, and doing so will disengage the Compressor. Sensor issues can be expected Especially if the system was not evacuated,,,, Vacuum pulled, prior to adding refrigerant after a repair.
Since you haven't Changed the Filter assembly, you need to do so before going forward. Having serviced your AC without changing the filter prior to puling a vacuum, you have contaminated the system.
Also check and clean the TEV again when you change the filter.
You could test and / or pass the low & high psi sensors, however exercise caution when bypassing the high side psi sensor !!! Best just to replace them. Since the system will be apart ti replace the filter etc., this would be a very good time to change the sensors.
Since you've also lost oil, it would be a good idea to drain the compressor oil and refill per spec.
Rent or Borrow a AC pump and pump the system, once you've reached the proper vacuum, for you year Vette, typically 27 Hg or 28-29 inches. Do run the pump operate for at least another 30 minutes. The Vacuum process removes the air from the pump, evap, etc. doing so also removes Moisture, which damages the filter.
There is a slight change that your Compressor Clutch mechanism is failing, IE. Slipping.
When your done, cut the bottom off the removed old Filter, take a look inside.
Rereading thread, I think you were still a little low. The pop hiss, I think comes from a valve in compressor moving. The high side pressure canbe low while the low side stays around 30" high side for simplicity high side should be 100 + ambient will be close..
Age 76 here, and I remember converting my '72 over to 134 but did that with the OEM condensor and evap, and valves, BUT when changing to serp drive ....I have a 'Denso'? compressor.......not an R4......so the trick was found for ME eventually to adjust some bolt/nut adjustment in the large valve near the evap coil.....on top ot the valve......sorry, but that all I recollect, having done this many years ago....but hopefully you sent in right direction on this.....it was to adjust the R12 valve setting more for 134.......and it worked well,
but as years went by of course the condenser failed, and so in went a more modern parallel flow for 134 and sure enuff it went super cold on discharge, with no other changes.....
OK, first of all no offense but some of you need to read closer.
I clearly stated I don't have my gauges at home, so yes I have gauges.
2nd my 93 had only ONE pressure switch low side. That is it. It does have a high side pressure sensor. We cannot assume things nor compare to other systems, that isn't how diagnostics work when its weird or odd. Has to be specific.
3rd, following up with 2nd point, I stated I replaced the accumulator when I did the condenser. It doesn't have filter. I've never heard or of seen a "filter" on an A/C system that isn't a term I associate with A/C systems. Nor does a 93 Corvette have a Thermal Expansion Valve. It has an orifice tube or OT for short. No idea what a TEV has to do with my 93 Corvette because it doesn't
The more I think about it I maybe having compressor failure or the poster that mentioned a seal letting in air but not leaking, that is a possibility I had not considered. I've seen far more odd things than a seal that leaks one way but not the next. Like EVAP systems, pressure is much different than vacuum.
For those that had good ideas, and helpful information. Thank you.
For those that tried but failed...stop please. Its painful to read.
I'm thinking of making a short video of the issue with gauges on the car with readings. That may clear up any questions for some.
Thank you for your inputs.
Not poking at you but any chance you confused a 12oz can as being a pound?
I don't mess with ac systems much but made that mistake once before because I simply assumed it was sold in 1lb cans.
Or.. The conversion rate for r134a isn't a static 75% of R12 volume, it is 75%-85% putting it at 27 oz to 30.6 oz. Might need closer to the 32 oz like the late 93 and 94+ r134 systems use.
[QUOTE=93Rubie;1601598002]OK, first of all no offense but some of you need to read closer.
I clearly stated I don't have my gauges at home, so yes I have gauges.
I'm not clear, you write has only one pressure switch, and then your write that it has a high pressure switch. All I can tell you is my C4 has both, Low and High sensors, aka pressure switches.
2nd my 93 had only ONE pressure switch low side. That is it. It does have a high side pressure sensor. We cannot assume things nor compare to other systems, that isn't how diagnostics work when its weird or odd. Has to be specific.
Please note on the attachments, a wiring diagram and a parts diagram, both indicate two ac sensors. Suggest that you obtain diagrams for your year C4 and note that some C4's have manual and some a climate control option, I don't know what years either may be an option or standard equipment, or what the exact differences in wiring other than the control are between these two. My Vettes, C4 and C5's, all have Climate Control.
3rd, following up with 2nd point, I stated I replaced the accumulator when I did the condenser. It doesn't have filter. I've never heard or of seen a "filter" on an A/C system that isn't a term I associate with A/C systems. Nor does a 93 Corvette have a Thermal Expansion Valve. It has an orifice tube or OT for short. No idea what a TEV has to do with my 93 Corvette because it doesn't
I missed that you replaced the Accumulator. Accumulators are often referred to as Filters. They have two functions, see below.
Note from a Tech Manual
""The accumulator is a part of the AC system, that is designed to remove debris, oil and moisture from the system, as well as prevent any remaining liquid refrigerant from returning to the compressor. The accumulator contains a desiccant that absorbs moisture. Once the desiccant is saturated then any additional moisture will pass through the entire AC system,""
Why I wrote about Vacuuming your system. And why I recommended to cut off the bottom.
A Thermal Expansion Valve is a Control Valve that can be regulated, force of habit. Many AC system utilize TEV vs a Fixed Control Valve. My point was to replace it while your during a tear down.
The more I think about it I maybe having compressor failure or the poster that mentioned a seal letting in air but not leaking, that is a possibility I had not considered. I've seen far more odd things than a seal that leaks one way but not the next. Like EVAP systems, pressure is much different than vacuum.
Possible, But I still think you need the proper electrical wiring diagram and follow the test procedure. On every AC I tested and been a part of, Bypassing the low pressure switch with a manual manual means with Gauges connected was an important test. Simple and quick. And while doing so, watching the compressor Clutch, they do fail. But when bypassing as I wrote DO watch the High Side Pressure. I don't recall that you wrote anything re loss or low pressure in your system.
If You can't find the exact year diagrams etc for you C4, then try ALLDATA, they have a complete service manual including Technical Service Bulletins on-line for about $30 a year. You can download any of their content, save and print. There's good step by step trouble shooting diagrams.
And consider electrical wiring or relays issues as well These can be intermittent and pesky buggers to track down, esp when the Car's ECM control the AC Clutch Control Relay. I recall that the ECM does cycle the AC system via relay control under certain circumstances, like WOT, Over Heating etc.
No offence taken, only trying to assist. I was certified in small and medium size AC ms during my Military Service, I served in a Mobil Field Unit. We had AC units to cool sensitive electronic equipment in our Vans. I took the AC course so our AC systems could be kept operation no matter what. I'm also a double degree Electrical / Electronic Engineer, retired with over two decades as Director. I spent my entire career in Computer and micro processor design and fabrication in industrial and harsh environments.
Good Luck,
OK, first of all no offense but some of you need to read closer.
I clearly stated I don't have my gauges at home, so yes I have gauges.
I'm not clear, you write has only one pressure switch, and then your write that it has a high pressure switch. All I can tell you is my C4 has both, Low and High sensors, aka pressure switches.
2nd my 93 had only ONE pressure switch low side. That is it. It does have a high side pressure sensor. We cannot assume things nor compare to other systems, that isn't how diagnostics work when its weird or odd. Has to be specific.
Please note on the attachments, a wiring diagram and a parts diagram, both indicate two ac sensors. Suggest that you obtain diagrams for your year C4 and note that some C4's have manual and some a climate control option, I don't know what years either may be an option or standard equipment, or what the exact differences in wiring other than the control are between these two. My Vettes, C4 and C5's, all have Climate Control.
3rd, following up with 2nd point, I stated I replaced the accumulator when I did the condenser. It doesn't have filter. I've never heard or of seen a "filter" on an A/C system that isn't a term I associate with A/C systems. Nor does a 93 Corvette have a Thermal Expansion Valve. It has an orifice tube or OT for short. No idea what a TEV has to do with my 93 Corvette because it doesn't
I missed that you replaced the Accumulator. Accumulators are often referred to as Filters. They have two functions, see below.
Note from a Tech Manual
""The accumulator is a part of the AC system, that is designed to remove debris, oil and moisture from the system, as well as prevent any remaining liquid refrigerant from returning to the compressor. The accumulator contains a desiccant that absorbs moisture. Once the desiccant is saturated then any additional moisture will pass through the entire AC system,""
Why I wrote about Vacuuming your system. And why I recommended to cut off the bottom.
A Thermal Expansion Valve is a Control Valve that can be regulated, force of habit. Many AC system utilize TEV vs a Fixed Control Valve. My point was to replace it while your during a tear down.
The more I think about it I maybe having compressor failure or the poster that mentioned a seal letting in air but not leaking, that is a possibility I had not considered. I've seen far more odd things than a seal that leaks one way but not the next. Like EVAP systems, pressure is much different than vacuum.
Possible, But I still think you need the proper electrical wiring diagram and follow the test procedure. On every AC I tested and been a part of, Bypassing the low pressure switch with a manual manual means with Gauges connected was an important test. Simple and quick. And while doing so, watching the compressor Clutch, they do fail. But when bypassing as I wrote DO watch the High Side Pressure. I don't recall that you wrote anything re loss or low pressure in your system.
If You can't find the exact year diagrams etc for you C4, then try ALLDATA, they have a complete service manual including Technical Service Bulletins on-line for about $30 a year. You can download any of their content, save and print. There's good step by step trouble shooting diagrams.
And consider electrical wiring or relays issues as well These can be intermittent and pesky buggers to track down, esp when the Car's ECM control the AC Clutch Control Relay. I recall that the ECM does cycle the AC system via relay control under certain circumstances, like WOT, Over Heating etc.
No offence taken, only trying to assist. I was certified in small and medium size AC ms during my Military Service, I served in a Mobil Field Unit. We had AC units to cool sensitive electronic equipment in our Vans. I took the AC course so our AC systems could be kept operation no matter what. I'm also a double degree Electrical / Electronic Engineer, retired with over two decades as Director. I spent my entire career in Computer and micro processor design and fabrication in industrial and harsh environments.
Good Luck,
Michael...
Dude, the charts and so forth might work for a 87 or something not even close for a 93. In my original post I talk about what it says in the FSM about a clogged orifice tube. So obviously I have a FSM.
Your terminology differs and that is fine. Mine is automotive based, no one refers to a accumulator as a filter.
Well folks this gets weirder. On Saturday may 30th it was about the same temperature it was this evening. About 65 degrees in the garage. Before I started the car I hooked up the gauges. Both reading about 68psi. Started car up and let warm up about 2 mins and turned on A/C. It is cycling off at about 22 psi. Kicks back on at 45 psi.
I'll upload videos later but all you'll see is a working system. Both at idle and 1500 to 2K rpms. Never missed a beat and never set a code. Duct temps around 35.
High side pressures around 175 when first started. They climbed as engine compartment temperature climber. After about 15 mins they where up around 200 and after 30 about 225 or so. Again low side cycling 22 off to 45 kicks on. Duct temps remained steady.
One noted after the car warmed up at idle it did NOT cycle on an off. Low side stayed around 25psi and high side about 215 or so. Only once I raised RPM did it start to cycle.
During this idle the low side was forming ice on piping. Melted once I raised RPM. I NEVER sit and idle this car very long with the A/C on and its never with the hood open. Under normal conditions I doubt ice would form on the piping.
I see nothing wrong with it right now with the gauges on. Tried it with them off. Worked perfectly fine.
I'm puzzled, what changed? Conditions where similar? I'll leave my gauges at home and if it acts up I'll test again. I'll also upload videos when I get a chance.
Here's a '93 AC on Corvette Forum dated 4-30-2009, see post #7,,,, schematics for manual and climate control, Trouble shooting guide, note the connector just after the trouble shooting guide.
The old mineral oil takes up condenser space, remove it it and replace with pag.
The filter use to be part of the metering device liquid line going to evaporator.
I think there is a weight adjustment going from 12 to 134 but don't know the amount.
OK, first of all no offense but some of you need to read closer.
I clearly stated I don't have my gauges at home, so yes I have gauges.
I'm not clear, you write has only one pressure switch, and then your write that it has a high pressure switch. All I can tell you is my C4 has both, Low and High sensors, aka pressure switches.
2nd my 93 had only ONE pressure switch low side. That is it. It does have a high side pressure sensor. We cannot assume things nor compare to other systems, that isn't how diagnostics work when its weird or odd. Has to be specific.
If I were 93Rubie, right about now I would be looking for a good rope and a bridge to jump off of reading some of this BS. He is soooo correct that some people need to READ and COMPREHEND! He clearly states it has 2 pressure switches, a high and a low, and yet people are confused.
The old mineral oil takes up condenser space, remove it it and replace with pag.
The filter use to be part of the metering device liquid line going to evaporator.
I think there is a weight adjustment going from 12 to 134 but don't know the amount.
3rd, following up with 2nd point, I stated I replaced the accumulator when I did the condenser. It doesn't have filter. I've never heard or of seen a "filter" on an A/C system that isn't a term I associate with A/C systems.
From my factory shop manual (it's for a 96):
At page 1B-5 (HVAC): Expansion Tube (Orfice): The plastic expansion tube (orfice), with its mesh screen and orfice, is located in the evaporator inlet pipe at the liquid line connection...The expansion tube and orfice are protected from contamination by filter screens on both inlet and outlet sides.".
At page 1B-6 (HVAC): The accumulator contains its own internal filter, Figure 3 - Accumulator.
At page 1B-4 (HVAC): "An aftermarket liquid line filter is available to protect higher mileage systems"
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A/C Compressor Short Cycling-Odd problem NOT low refridgerant issue
