AMC Eagle Den Forum

The Shop => Under the Hood & HVAC => Topic started by: JONAS78028 on July 18, 2017, 10:21:25 AM

Title: What cycles the AC compressor?
Post by: JONAS78028 on July 18, 2017, 10:21:25 AM
I'm getting ready to convert my AC system over to 134a.  I have a new drier and expansion valve on my workbench and plan to flush the system and drain the compressor of old oil.
My question is... What cycles the compressor on and off?  Shouldn't there be a pressure switch somewhere?  I'm going to go back and look again but I didn't see one.
Title: Re: What cycles the AC compressor?
Post by: amcfool1 on July 18, 2017, 01:09:48 PM
hi, afaik, with the switch in either AC, or, Max AC position, just turning the fan on activates the system, ie, turns on your ac. good luck, gz
Title: Re: What cycles the AC compressor?
Post by: eaglefreek on July 18, 2017, 02:08:37 PM
There should be a low pressure and/or high pressure switch, but I no longer have an Eagle to look. Here's another thread. http://forums.amceaglesden.com/index.php?topic=43466.0
Title: Re: What cycles the AC compressor?
Post by: AMC of Houston on July 18, 2017, 05:49:39 PM
I forgot what year your car was -- but if its an '82 or later, with factory AC, and a 6-cylinder; the switch should be in the line close up by the dryer (left front of the engine bay).
Title: Re: What cycles the AC compressor?
Post by: vangremlin on July 18, 2017, 06:00:24 PM
What year is your Eagle?  I'm not an expert on AC, but it is my understanding that for the earlier Eagles (pre 84 or 85) with the York compressors, there was no pressure switch.  The pressure switch on the later Eagles was to the left (driver's side) of the radiator where the hoses come through for the condenser, and it fed into the power feed to the compressor.

I converted to the Sanden (rotary) compressor from an 85 Eagle when the York compressor on my 80 Eagle coupe went bad.  I wanted to put that pressure switch into one of the AC hoses on my Eagle, but couldn't find a shop to make a short adaptor hose that would connect with the existing hoses.  It would have required making a full new hose and I didn't want to go through the bother of pulling the AC box in the car to attach the new hose, so I went without the switch.

As far as activating the compressor, its like amcfool1 says, turning on the fan while its in AC or Max AC position will turn on the compressor.  I think the AC "thermostat" (not the right term, but its the little probe that sticks into the evaporator) will then turn the compressor off once the desired temp is reached.

Good luck!
Title: Re: What cycles the AC compressor?
Post by: mo.eagles on July 18, 2017, 07:22:43 PM
There is a low pressure switch at the sight glass . It is located on the drivers side of the radiator .
Title: Re: What cycles the AC compressor?
Post by: JONAS78028 on July 19, 2017, 08:37:33 AM
I found it... as per previous post above... it's on the drivers side of the radiator right where I overlooked it...   ::)
 Thanks everybody!
Title: Re: What cycles the AC compressor?
Post by: JONAS78028 on July 19, 2017, 03:51:49 PM
The AC system on this Eagle actually has a charge... just not enough to cool things down.  It's been so long since I have messed with an R12 system that I totally didn't consider simply adding R12 to this vehicle.    Everything that I've worked on lately either has 134a or has already been converted.  Now I just need to find adapter fittings for my gauge set...
Title: Re: What cycles the AC compressor?
Post by: trucker79005 on July 20, 2017, 12:12:48 PM
The AC system on this Eagle actually has a charge... just not enough to cool things down.  It's been so long since I have messed with an R12 system that I totally didn't consider simply adding R12 to this vehicle.    Everything that I've worked on lately either has 134a or has already been converted.  Now I just need to find adapter fittings for my gauge set...

Where were you able to find the r12? I've been looking on ebay and don't want to get ripped off but I have my Eagle and a 71 ford pickup that haven't been converted yet.
Title: Re: What cycles the AC compressor?
Post by: eaglefreek on July 20, 2017, 12:36:30 PM
The AC system on this Eagle actually has a charge... just not enough to cool things down.  It's been so long since I have messed with an R12 system that I totally didn't consider simply adding R12 to this vehicle.    Everything that I've worked on lately either has 134a or has already been converted.  Now I just need to find adapter fittings for my gauge set...
If you can keep it R12 that is the best thing to do. With r134, my Eagle cooled mediocre at best.

The AC system on this Eagle actually has a charge... just not enough to cool things down.  It's been so long since I have messed with an R12 system that I totally didn't consider simply adding R12 to this vehicle.    Everything that I've worked on lately either has 134a or has already been converted.  Now I just need to find adapter fittings for my gauge set...

Where were you able to find the r12? I've been looking on ebay and don't want to get ripped off but I have my Eagle and a 71 ford pickup that haven't been converted yet.
Try Craigslist. There was 4 cases somewhat local to me about a month ago. The guy wanted $150 for a case of 12. I was going to buy all four, but they sold before I got back into town. They typically sell for about $25 a can near me, but I've seen them cheaper and some have wanted $40-50 a can.
Title: Re: What cycles the AC compressor?
Post by: AMC of Houston on July 20, 2017, 07:46:35 PM
I use one of those "heavy-on-the-butane" "drop-in" R12 replacements (currently use the Freeze-12 brand, 'cus I got a bargain on a few cases a while back).    Then there are those who tell me my car will explode using this stuff; but I'm not worried since I'm sitting on 15 gallons or so of high explosive every time I go for a drive!!    Your mileage (or fireball) may vary........
Title: Re: What cycles the AC compressor?
Post by: trucker79005 on July 21, 2017, 11:02:20 AM
Try Craigslist. There was 4 cases somewhat local to me about a month ago. The guy wanted $150 for a case of 12. I was going to buy all four, but they sold before I got back into town. They typically sell for about $25 a can near me, but I've seen them cheaper and some have wanted $40-50 a can.
Not really sure why I hadn't tried craigslist yet. I look on there for everything else..
I use one of those "heavy-on-the-butane" "drop-in" R12 replacements (currently use the Freeze-12 brand, 'cus I got a bargain on a few cases a while back).    Then there are those who tell me my car will explode using this stuff; but I'm not worried since I'm sitting on 15 gallons or so of high explosive every time I go for a drive!!    Your mileage (or fireball) may vary........
>:D I'll have to look into it. Is the "drop in" compatible enough that I could have someone use this first and then once i know the system isn't leaking use the real stuff?? I haven't figured out any other real good way to tell if my system is good other than charging with nitrogen and I'm not having a lot of luck getting that done.
Title: Re: What cycles the AC compressor?
Post by: AMC of Houston on July 21, 2017, 12:30:09 PM
Supposedly the drop-ins are compatible and mixable per their sales drivel.   I know I've done in on my '85 Eagle with no issues.
Title: Re: What cycles the AC compressor?
Post by: eaglefreek on July 21, 2017, 03:09:22 PM
One issue with mixing them is if you ever need to get it serviced, you may have a hard time finding someone who will evacuate the system for you.
Title: Re: What cycles the AC compressor?
Post by: AMC of Houston on July 21, 2017, 07:14:24 PM
Unless you don't tell them what's in it!!    >:D      I have a vacuum pump.............
Title: Re: What cycles the AC compressor?
Post by: JONAS78028 on July 22, 2017, 10:37:22 PM
Where were you able to find the r12? I've been looking on ebay and don't want to get ripped off but I have my Eagle and a 71 ford pickup that haven't been converted yet.
I actually have a stash of R12  ;D
I'm so used to having to replace bad compressors that I am just in the habit of converting systems over to 134a.  This car came to me with a sealed R12 system that was good so I just pulled a vacuum and charged it. 
Title: Re: What cycles the AC compressor?
Post by: JONAS78028 on July 22, 2017, 10:42:36 PM
Well, I got it working... woohoo!
There was very little charge in it so I pulled a vacuum for an hour and let it sit overnight.  I put in 28 ounces of R12 and it's putting out 44 degrees out of the dash vents.    I may try to fine tune it later but I'm pretty happy with that for now. 
Title: Re: What cycles the AC compressor?
Post by: trucker79005 on July 22, 2017, 11:26:39 PM
I actually have a stash of R12  ;D
I'm so used to having to replace bad compressors that I am just in the habit of converting systems over to 134a.  This car came to me with a sealed R12 system that was good so I just pulled a vacuum and charged it.
I haven't read enough yet to figure out how to tell if my system is good without charging it... The mechanic I was planning on using said he really didn't have a way and that pulling the vacuum would only tell him it didn't have a Big leak. Said the only way to know how it would handle hot days and high pressure was too charge it and i don't have a stash :-\

I did look on craigslist and most of it is outrageous but I did find a 30 lb canister that if I could figure out how to get it i think I could get the mechanic to go in on it with me..lot of money up front though.
Title: Re: What cycles the AC compressor?
Post by: AMC1 on July 24, 2017, 03:26:50 PM
I don't know why more fellows don't switch over to R134a. I bought an AC system a few years ago & switched it over before installation. Admitedly  I have a small nasty leak which requires 4-6 ounces per season. I filled it a couple of weeks ago & its very cold in the car. I purchased (5) 12 ounce cans for $4.89 each but could have bought a 100. That should last 10 years If I never get around to fixing that leak.
Title: Re: What cycles the AC compressor?
Post by: trucker79005 on July 24, 2017, 06:19:02 PM
I'm curious what you mean. What components did you buy and what kind of money did you put into switching? I was looking at compressors and driers and they don't seem too cheap.
Title: Re: What cycles the AC compressor?
Post by: mo.eagles on July 24, 2017, 08:26:47 PM
Those AMC Jeep/Renault  cans might be worth something . Museum quality .
Title: Re: What cycles the AC compressor?
Post by: rollguy on July 24, 2017, 09:37:37 PM
I'm so used to having to replace bad compressors that I am just in the habit of converting systems over to 134a.  This car came to me with a sealed R12 system that was good so I just pulled a vacuum and charged it.
If the system was empty enough to pull a vacuum, then for sure you have a leak. If the system had a quantity of R12 in it before vacuuming, then pulling a vacuum is akin to releasing refrigerant (venting), and is illegal. It is wise to pressurize the empty system with nitrogen and check for leaks (and fix them) before charging. With the cost of R12 (and the scarcity of it), it is best to ensure there is no leaks. As far as those "designer" refrigerants (Dura-cool, Freeze 12 etc) go, they are not "drop in" as they claim they are. Most are blends, and blends leak at different rates (different size molecules). They also are not compatible with some oils that may be in your system.  It is always best to start from scratch and do it right the first time. Find leaks first, replace leaky components (hoses especially), flush remaining components (drain the oil from the compressor-not flush), check for leaks again, and then charge with the proper amount of oil and refrigerant. Never use vacuum for checking leaks!!!  Always replace the receiver/drier, Orings (oil them), and expansion valve (especially if changing to a different refrigerant).  Doing it right the first time will insure many years of service without any maintenance. Also, changing the condenser to a Parallel Flow type will make the system more efficient with R134a. They are fairly inexpensive, and well worth the effort as a cooling upgrade.
Title: Re: What cycles the AC compressor?
Post by: trucker79005 on July 25, 2017, 12:32:58 AM
If the system was empty enough to pull a vacuum, then for sure you have a leak. If the system had a quantity of R12 in it before vacuuming, then pulling a vacuum is akin to releasing refrigerant (venting), and is illegal. It is wise to pressurize the empty system with nitrogen and check for leaks (and fix them) before charging.
I've been looking for someone to pressure test with nitrogen and not having much luck. Is it common practice?
Title: Re: What cycles the AC compressor?
Post by: JONAS78028 on July 25, 2017, 09:31:12 AM
Those AMC Jeep/Renault  cans might be worth something . Museum quality .
Hmmm...  I didn't think about that.  I actually threw the used cans away... dang.

If the system was empty enough to pull a vacuum, then for sure you have a leak. If the system had a quantity of R12 in it before vacuuming, then pulling a vacuum is akin to releasing refrigerant (venting), and is illegal. It is wise to pressurize the empty system with nitrogen and check for leaks (and fix them) before charging. With the cost of R12 (and the scarcity of it), it is best to ensure there is no leaks. As far as those "designer" refrigerants (Dura-cool, Freeze 12 etc) go, they are not "drop in" as they claim they are. Most are blends, and blends leak at different rates (different size molecules). They also are not compatible with some oils that may be in your system.  It is always best to start from scratch and do it right the first time. Find leaks first, replace leaky components (hoses especially), flush remaining components (drain the oil from the compressor-not flush), check for leaks again, and then charge with the proper amount of oil and refrigerant. Never use vacuum for checking leaks!!!  Always replace the receiver/drier, Orings (oil them), and expansion valve (especially if changing to a different refrigerant).  Doing it right the first time will insure many years of service without any maintenance. Also, changing the condenser to a Parallel Flow type will make the system more efficient with R134a. They are fairly inexpensive, and well worth the effort as a cooling upgrade.
Good advice!
Title: Re: What cycles the AC compressor?
Post by: rollguy on July 25, 2017, 10:44:52 AM
If the system was empty enough to pull a vacuum, then for sure you have a leak. If the system had a quantity of R12 in it before vacuuming, then pulling a vacuum is akin to releasing refrigerant (venting), and is illegal. It is wise to pressurize the empty system with nitrogen and check for leaks (and fix them) before charging.
I've been looking for someone to pressure test with nitrogen and not having much luck. Is it common practice?
I would think that every A/C shop would have the equipment and would do it for you. Yes it is common industry practice, as well as mandated by the EPA. R12 is not manufactured anymore, and the only available source is NOS or reclaimed.  Once it is all gone, there is no more.  Fixing leaks to preserve what supplies that remain, is wise both environmentally, and economically.
Title: Re: What cycles the AC compressor?
Post by: hatzie on May 05, 2018, 02:30:18 PM
If the system was empty enough to pull a vacuum, then for sure you have a leak. If the system had a quantity of R12 in it before vacuuming, then pulling a vacuum is akin to releasing refrigerant (venting), and is illegal. It is wise to pressurize the empty system with nitrogen and check for leaks (and fix them) before charging.
I've been looking for someone to pressure test with nitrogen and not having much luck. Is it common practice?

Sorry to bring this back from the dead.  but this may be useful to someone.
It's common to use inert dry gasses to pressure test a system.  Garages tend to use Nitrogen for some reason.
You don't have to use Nitrogen to test for leaks.  Just don't use refrigerant.
Any known-dry non-reactive gas that shouldn't be called a refrigerant by the EPA will do the job.
I use Argon from my TIG setup.  It's readily available, to me, since I happen to have two 125cf Argon bottles for the TIG and two Argon CO2 blend bottles along with one straight CO2 bottle for MIG welding. 
If you do party balloons or weld with exotic gasses...  Helium from a bottle will work too. 

Shop air ain't dry so you can't use that.
Propane is also known to the EPA as R290 refrigerant. so you can't use that even though it's not ozone depleting.
Title: Re: What cycles the AC compressor?
Post by: mudkicker715 on May 05, 2018, 06:10:20 PM
No problems with bringing back an old thread. Also if you can pull vacuum on a system over night that helps to get rid of any moisture.