A/C Issues
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Joined: Aug 2025
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A/C Issues
93 C4 40th Anniversary Model.
Old issue: A/C Cycles On and Off about every 2- 10 seconds. There is plenty of Freon. Throws 09 error code (low freon). Air in car is cold and it even blows just as cold when system is OFF.
System has been converted to the R134 Freon.
I replaced the Low Pressure Switch. Seams to have fixed the cycling on and off issue
New problem: New low pressure switch stopped the A/C from cycling on and off. But now it does not cycle on at all. Freon gauge say close to 60 psi at the high end but because the system does not cycle on I can't get the low pressure reading. No cold air blows.
Someone at some time unplugged the High Pressure switch and jumped the connector with a paper clip, I replaced the High pressure switch nothing has changed.
Any other ideas of what could be the problem? Bad high pressure connector. Relay issue?
When Cold starting, the fan runs until up to temperature then turns off.
Not sure if these 2 systems are somehow connected or if there are 2 different issue happening.
Any help will be appreciated.
Thank you
Old issue: A/C Cycles On and Off about every 2- 10 seconds. There is plenty of Freon. Throws 09 error code (low freon). Air in car is cold and it even blows just as cold when system is OFF.
System has been converted to the R134 Freon.
I replaced the Low Pressure Switch. Seams to have fixed the cycling on and off issue
New problem: New low pressure switch stopped the A/C from cycling on and off. But now it does not cycle on at all. Freon gauge say close to 60 psi at the high end but because the system does not cycle on I can't get the low pressure reading. No cold air blows.
Someone at some time unplugged the High Pressure switch and jumped the connector with a paper clip, I replaced the High pressure switch nothing has changed.
Any other ideas of what could be the problem? Bad high pressure connector. Relay issue?
When Cold starting, the fan runs until up to temperature then turns off.
Not sure if these 2 systems are somehow connected or if there are 2 different issue happening.
Any help will be appreciated.
Thank you
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
93 C4 40th Anniversary Model.
Old issue: A/C Cycles On and Off about every 2- 10 seconds. There is plenty of Freon. Throws 09 error code (low freon). Air in car is cold and it even blows just as cold when system is OFF.
System has been converted to the R134 Freon.
I replaced the Low Pressure Switch. Seams to have fixed the cycling on and off issue
New problem: New low pressure switch stopped the A/C from cycling on and off. But now it does not cycle on at all. Freon gauge say close to 60 psi at the high end but because the system does not cycle on I can't get the low pressure reading. No cold air blows.
Someone at some time unplugged the High Pressure switch and jumped the connector with a paper clip, I replaced the High pressure switch nothing has changed.
Any other ideas of what could be the problem? Bad high pressure connector. Relay issue?
When Cold starting, the fan runs until up to temperature then turns off.
Not sure if these 2 systems are somehow connected or if there are 2 different issue happening.
Any help will be appreciated.
Thank you
Old issue: A/C Cycles On and Off about every 2- 10 seconds. There is plenty of Freon. Throws 09 error code (low freon). Air in car is cold and it even blows just as cold when system is OFF.
System has been converted to the R134 Freon.
I replaced the Low Pressure Switch. Seams to have fixed the cycling on and off issue
New problem: New low pressure switch stopped the A/C from cycling on and off. But now it does not cycle on at all. Freon gauge say close to 60 psi at the high end but because the system does not cycle on I can't get the low pressure reading. No cold air blows.
Someone at some time unplugged the High Pressure switch and jumped the connector with a paper clip, I replaced the High pressure switch nothing has changed.
Any other ideas of what could be the problem? Bad high pressure connector. Relay issue?
When Cold starting, the fan runs until up to temperature then turns off.
Not sure if these 2 systems are somehow connected or if there are 2 different issue happening.
Any help will be appreciated.
Thank you
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
Drifting
Joined: Jun 2013
Posts: 1,957
Likes: 342
From: Shell Point (Crawfordville) Florida
09 code means low Freon. And the system recycles very frequently. You do NOT have plenty of Freon. You are LOW on Freon.
With an 09 code the compressor will not come on unless the system (computer) is reset. You do that by disconnecting the battery for 30 sec. or so, then bypass the LOW pressure switch, start the car and turn on the AC and the compressor should come on. Then refill the system. The compressor will go on and off recycle rapidly) until there is sufficient Freon in it, then it will stay on. Then disconnect your low pressure bypass and reconnect the plug into it.
Then you have to find the source of the Freon leak.
And measuring pressures, either high or low without the compressor running is meaningless - you are measuring a static system pressure which is equal throughout the system.
With an 09 code the compressor will not come on unless the system (computer) is reset. You do that by disconnecting the battery for 30 sec. or so, then bypass the LOW pressure switch, start the car and turn on the AC and the compressor should come on. Then refill the system. The compressor will go on and off recycle rapidly) until there is sufficient Freon in it, then it will stay on. Then disconnect your low pressure bypass and reconnect the plug into it.
Then you have to find the source of the Freon leak.
And measuring pressures, either high or low without the compressor running is meaningless - you are measuring a static system pressure which is equal throughout the system.
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
09 code means low Freon. And the system recycles very frequently. You do NOT have plenty of Freon. You are LOW on Freon.
With an 09 code the compressor will not come on unless the system (computer) is reset. You do that by disconnecting the battery for 30 sec. or so, then bypass the LOW pressure switch, start the car and turn on the AC and the compressor should come on. Then refill the system. The compressor will go on and off recycle rapidly) until there is sufficient Freon in it, then it will stay on. Then disconnect your low pressure bypass and reconnect the plug into it.
Then you have to find the source of the Freon leak.
And measuring pressures, either high or low without the compressor running is meaningless - you are measuring a static system pressure which is equal throughout the system.
With an 09 code the compressor will not come on unless the system (computer) is reset. You do that by disconnecting the battery for 30 sec. or so, then bypass the LOW pressure switch, start the car and turn on the AC and the compressor should come on. Then refill the system. The compressor will go on and off recycle rapidly) until there is sufficient Freon in it, then it will stay on. Then disconnect your low pressure bypass and reconnect the plug into it.
Then you have to find the source of the Freon leak.
And measuring pressures, either high or low without the compressor running is meaningless - you are measuring a static system pressure which is equal throughout the system.
Burning Brakes
Joined: Aug 2008
Posts: 823
Likes: 216
From: Tampa, FL
If you don't have it... best thing in my opinion is to get a set of MVAC gauges if you don't already have them. They have the high and low connector that allows you to connect a can of freon and fill at both ends. In many cases, I've had to put a paper clip in the low-pressure switch connector to keep the compressor running while I add freon. You probably already have that, but just wanted to throw that out there in case you're using one of the "quick fill" low side connectors with the integrated gauges.
Quick question... how long has it been leaking freon? If it was converted, I'm guessing the seals aren't that old... but I've seen shops do a half-*** job replacing the seals, usually not bothering to replace the tubes and connections that are hard to get to (they're all pretty much right there though on the C4). The valve stems also sometimes leak, and I've found that this seems to be where most of my leaks have been from. If you end up at some point with the system being completely low again, I'd just evacuate everything and use that opportunity to replace all the seals and valves.
Quick question... how long has it been leaking freon? If it was converted, I'm guessing the seals aren't that old... but I've seen shops do a half-*** job replacing the seals, usually not bothering to replace the tubes and connections that are hard to get to (they're all pretty much right there though on the C4). The valve stems also sometimes leak, and I've found that this seems to be where most of my leaks have been from. If you end up at some point with the system being completely low again, I'd just evacuate everything and use that opportunity to replace all the seals and valves.
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Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
If you don't have it... best thing in my opinion is to get a set of MVAC gauges if you don't already have them. They have the high and low connector that allows you to connect a can of freon and fill at both ends. In many cases, I've had to put a paper clip in the low-pressure switch connector to keep the compressor running while I add freon. You probably already have that, but just wanted to throw that out there in case you're using one of the "quick fill" low side connectors with the integrated gauges.
Quick question... how long has it been leaking freon? If it was converted, I'm guessing the seals aren't that old... but I've seen shops do a half-*** job replacing the seals, usually not bothering to replace the tubes and connections that are hard to get to (they're all pretty much right there though on the C4). The valve stems also sometimes leak, and I've found that this seems to be where most of my leaks have been from. If you end up at some point with the system being completely low again, I'd just evacuate everything and use that opportunity to replace all the seals and valves.
Quick question... how long has it been leaking freon? If it was converted, I'm guessing the seals aren't that old... but I've seen shops do a half-*** job replacing the seals, usually not bothering to replace the tubes and connections that are hard to get to (they're all pretty much right there though on the C4). The valve stems also sometimes leak, and I've found that this seems to be where most of my leaks have been from. If you end up at some point with the system being completely low again, I'd just evacuate everything and use that opportunity to replace all the seals and valves.
Drifting
Joined: Jun 2013
Posts: 1,957
Likes: 342
From: Shell Point (Crawfordville) Florida
You're right. What I meant to say is to bypass the low pressure switch to get the compressor to turn on so that you can add some Freon into the system. You cannot add Freon unless the compressor is running. Once you get a reasonable amount in, remove the bypass, reconnect the plug, and add the proper amount according to the low side pressure. The compressor will cycle on and off until the system is filled, then will just run continously.
Safety Car
Joined: May 2001
Posts: 4,741
Likes: 1,639
From: Fairfax Virginia
Freon is a very leak prone material. If there is any place for a leak then it will be gone in no time. I would put some dye in the system and look for any leaks in your system.
Having a set of AC Gauges is very important if you ever service the AC system. I also have a small 2 stage vacuum pump to pull the vacuum in the system to verify it is sealed really well. I would pull the vacuum and wait for 2-3 days before moving on just to be sure I don't have any leaks in the system. Harbor Freight has the vacuum gauges as well as the vacuum pumps for reasonable prices on chinese tools.
I converted my 1988 C4 a long time ago and it has been great ever since using R134 and the original style condenser with no problems and lots of cold air. Then when TRAK Auto closed up I was able to buy almost three cases of R134 at .99 cents a can which turned into a wise purchase.
Don't forget to replace the drier on the system if you open it up for any reason. Converting the system to R134 was not hard or expensive as I did in my driveway. R134 worked really well in my AC system and provides a cool cabin during the hottest of days.
Having a set of AC Gauges is very important if you ever service the AC system. I also have a small 2 stage vacuum pump to pull the vacuum in the system to verify it is sealed really well. I would pull the vacuum and wait for 2-3 days before moving on just to be sure I don't have any leaks in the system. Harbor Freight has the vacuum gauges as well as the vacuum pumps for reasonable prices on chinese tools.
I converted my 1988 C4 a long time ago and it has been great ever since using R134 and the original style condenser with no problems and lots of cold air. Then when TRAK Auto closed up I was able to buy almost three cases of R134 at .99 cents a can which turned into a wise purchase.
Don't forget to replace the drier on the system if you open it up for any reason. Converting the system to R134 was not hard or expensive as I did in my driveway. R134 worked really well in my AC system and provides a cool cabin during the hottest of days.
Burning Brakes
Joined: Aug 2008
Posts: 823
Likes: 216
From: Tampa, FL
The gauges will come with instructions that are easy to follow… and there are plenty of YouTube tutorials, sometimes by the tool manufacturers themselves. Remember, it’s not rocket science, anyone can do it.
Here’s an example of what you need:
https://www.amazon.com/Diagnostic-Manifold-Charging-Refrigerants-Adjustable/dp/B08V8L2JKD/
Burning Brakes
Joined: Aug 2008
Posts: 823
Likes: 216
From: Tampa, FL
Freon is a very leak prone material. If there is any place for a leak then it will be gone in no time. I would put some dye in the system and look for any leaks in your system.
Having a set of AC Gauges is very important if you ever service the AC system. I also have a small 2 stage vacuum pump to pull the vacuum in the system to verify it is sealed really well. I would pull the vacuum and wait for 2-3 days before moving on just to be sure I don't have any leaks in the system. Harbor Freight has the vacuum gauges as well as the vacuum pumps for reasonable prices on chinese tools.
I converted my 1988 C4 a long time ago and it has been great ever since using R134 and the original style condenser with no problems and lots of cold air. Then when TRAK Auto closed up I was able to buy almost three cases of R134 at .99 cents a can which turned into a wise purchase.
Don't forget to replace the drier on the system if you open it up for any reason. Converting the system to R134 was not hard or expensive as I did in my driveway. R134 worked really well in my AC system and provides a cool cabin during the hottest of days.
Having a set of AC Gauges is very important if you ever service the AC system. I also have a small 2 stage vacuum pump to pull the vacuum in the system to verify it is sealed really well. I would pull the vacuum and wait for 2-3 days before moving on just to be sure I don't have any leaks in the system. Harbor Freight has the vacuum gauges as well as the vacuum pumps for reasonable prices on chinese tools.
I converted my 1988 C4 a long time ago and it has been great ever since using R134 and the original style condenser with no problems and lots of cold air. Then when TRAK Auto closed up I was able to buy almost three cases of R134 at .99 cents a can which turned into a wise purchase.
Don't forget to replace the drier on the system if you open it up for any reason. Converting the system to R134 was not hard or expensive as I did in my driveway. R134 worked really well in my AC system and provides a cool cabin during the hottest of days.
This is the pump he’s talking about;
(note, it comes with the gauges in the previous link)
Melting Slicks
Joined: Feb 2003
Posts: 2,661
Likes: 806
From: Saskatoon Sask.
No problem. In response to what someone else above said, make sure you get the gauge set that has two gauges. I don’t think they even sell the single gauge set anymore. You don’t have to worry about blowing a can. It’s pretty normal to fill on both sides when you’re filling it from really low. Topping it off should be done on the low side. Just monitor the pressure on the high side, and close the high-side valve as it reaches pressure. Then, let it continue to fill from the low side until the can and pressure equalizes, close the valve, and put on a new can. For cans that come with oil, they should be upside down when you fill so it draws in the oil too.
The gauges will come with instructions that are easy to follow… and there are plenty of YouTube tutorials, sometimes by the tool manufacturers themselves. Remember, it’s not rocket science, anyone can do it.
Here’s an example of what you need:
https://www.amazon.com/Diagnostic-Ma...dp/B08V8L2JKD/
The gauges will come with instructions that are easy to follow… and there are plenty of YouTube tutorials, sometimes by the tool manufacturers themselves. Remember, it’s not rocket science, anyone can do it.
Here’s an example of what you need:
https://www.amazon.com/Diagnostic-Ma...dp/B08V8L2JKD/
Please!! Stop it!! It is NOT "pretty normal" to fill from both sides. Obviously, you have no formal training in refrigeration. Except for evacuation, you should never have both valves open at the same time. When you do this, you have provided a direct route from the high side to the low side. Since the high pressure port is after the compressor, the higher pressure can force LIQUID refrigerant through to the low side port which is before the compressor. Liquid cannot be compressed. That is the main job of an accumulator - to insure liquid does not reach the compressor. Likewise, you tell him to fill with the can upside down. This feeds 100% liquid and must only be done on the high side. Hard to do that when you have both valves open. 100% liquid also going to low side.
Last edited by arbee; Sep 27, 2025 at 09:06 AM.
Burning Brakes
Joined: Jan 2019
Posts: 1,225
Likes: 682
From: Park City, TN
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Several auto parts store chains "rent" the gauges and pump.
Pro
Joined: Jul 2023
Posts: 527
Likes: 274
From: Marysville WA
Iron Mike says "Everyone has a plan until they get punched in the mouth", or in this case have a can of freon explode in your face.
To some servicing your own A/C may seem so simple anyone can do it, but if someone dies or gets gravely injured due to inexperience or just plain idiocy I wouldn't want to be the one who encouraged that person.
i purchased some cans of R12 and a vintage fill hose thinking I could recharge my '84 myself. After reading many posts on this forum, Especially ones that Arbee has participated in, I no longer have any desire to mess with it and just roll the window down. So far so good.
Thanks Arbee! I hope more members listen to your (correct) advice.
To some servicing your own A/C may seem so simple anyone can do it, but if someone dies or gets gravely injured due to inexperience or just plain idiocy I wouldn't want to be the one who encouraged that person.
i purchased some cans of R12 and a vintage fill hose thinking I could recharge my '84 myself. After reading many posts on this forum, Especially ones that Arbee has participated in, I no longer have any desire to mess with it and just roll the window down. So far so good.
Thanks Arbee! I hope more members listen to your (correct) advice.
Last edited by typical boomer; Sep 27, 2025 at 10:16 PM.
Burning Brakes
Joined: Aug 2008
Posts: 823
Likes: 216
From: Tampa, FL
I'm just curious how you were able to get R12, it requires a license to be able to purchase it since it's controlled. It was either a LONG time ago, or you're not being totally honest.
You're basically saying that Arbee scared you into thinking that working on an MVAC system is so difficult, that you just gave up and now just roll down your window with a perpetually broken MVAC system. No offense, but I get frustrated with the preponderance of Corvette owners who don't actually work on their own cars. I almost don't understand what the point of a forum is, if you're not going to actually work on the car yourself. Working on the AC system is NOT hard. Don't let Arbee scare you. Yes, he has a lot of experience. I've replaced the entire AC system in at least 7 cars. It's not what I do for a living, but they've all worked perfectly. Just like cutting tile, or patching drywall, or sweating pipes. There's a reason why none of this requires a degree. I'm not trying to be mean, but damn...
Last edited by 82-T/A; Sep 27, 2025 at 10:32 PM.