and 12 is colder than 134 in a old system. 
AC Compressor will not cycle off
Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
AC Compressor will not cycle off
On my 1985, when the AC is turned on, the compressor engages and cold air comes out. But, even after the interior is cold, the compressor will not cycle off. The clutch remains engaged. The cooling fan stays on, but will turn off for a moment and then start back up. It does not stay off for more that a few seconds. Any Ideas? The system was converted to 134Ra back in 1988.
Last edited by J H; Dec 25, 2015 at 01:16 PM.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Possibly the cycling switch could be bad and not opening up at the correct pressure. Putting a set of gauges on it will really tell the story. If the pressure is below 20 psi heading south, the switch is probably bad. Look for about 22psi on the low side for the switch to open which is about the norm.
The system should cycle more with a low fan setting and if you raise the RPM it should cycle off more frequently (than a high fan setting).
Actually when it is cooler outside the system cycles more as the low side will get down there much quicker and switch opens up. When it's hot outside all pressures are higher and the compressor and system has to work harder to get to the cut of pressure. (Air flow over the condenser is a big factor as well).
Most of the switches I have changed over the years went bad at it cycled at a to lower pressure and compressor runs excessively.
The system should cycle more with a low fan setting and if you raise the RPM it should cycle off more frequently (than a high fan setting).
Actually when it is cooler outside the system cycles more as the low side will get down there much quicker and switch opens up. When it's hot outside all pressures are higher and the compressor and system has to work harder to get to the cut of pressure. (Air flow over the condenser is a big factor as well).
Most of the switches I have changed over the years went bad at it cycled at a to lower pressure and compressor runs excessively.
Last edited by pcolt94; Dec 25, 2015 at 08:43 PM.
Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
Thanks for these replies. I was thinking that one of the switches had gone bad also. I will look into that further. All of the AC switches are original and I guess it is about time for a malfunction. Thanks for confirming that I was thinking in the right direction as far as a place to begin my investigation.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Might be just a little low on refrigerant. Like pcolt94 said, put some gauges on it. They'll tell you the story!
Do you see any frost on the suction line at the evap coils after the system has been running awhile?
Do you see any frost on the suction line at the evap coils after the system has been running awhile?
Last edited by Hot Rod Roy; Dec 26, 2015 at 02:05 AM.
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Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
Will work with the gauges when I get some time in the next day or so. And, the line at the evaporator has not frosted up, but there is plenty of condensation on it and it does get real cold.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Is this a current observation of the compressor, or a difference of operation from the past. I assume when you turn the AC off the compressor stops.
Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
The system is blowing cold air, low side pipe not icing up and compressor running are good signs of a system working normal.
Is this a current observation of the compressor, or a difference of operation from the past. I assume when you turn the AC off the compressor stops.
Is this a current observation of the compressor, or a difference of operation from the past. I assume when you turn the AC off the compressor stops.
An A/C thread in December from a guy in NC , Strange....
..WW
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Yes, this is a current observation. And, yes, the compressor does turn off when I turn the AC off. Just checked the pressure and it was high -- around 30psi. I bled a little off and upped the idle. The compressor did cycle off for a moment. I am now satisfied that the system is OK (I think). So, I am leaving it alone until I can run it more while driving and see if it seems ok. The air is cold. Thanks to all.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Yes, this is a current observation. And, yes, the compressor does turn off when I turn the AC off. Just checked the pressure and it was high -- around 30psi. I bled a little off and upped the idle. The compressor did cycle off for a moment. I am now satisfied that the system is OK (I think). So, I am leaving it alone until I can run it more while driving and see if it seems ok. The air is cold. Thanks to all.
The pressures of an AC system while operating are always moving up and down. It never really stays in one place. As the pressure in the low side reaches 22 psi the switch opens and the compressor stops. The pressure then starts to rise to about 46 psi where the cycling switch then closes and the compressor starts and the whole cycle starts again.
Freon is not like air. For a given temperature there is a given pressure. That’s why there is a pressure chart for all refrigeration gases. It's not like putting air in a tire where the pressure goes down when air is removed. That’s why the static pressure in a system is dependent on the ambient temperature around it.
Removing gas is not what you really want to do as you will not really see a change in pressure. You could end up with pipes freezing over. But what it will affect is how the whole system operates, compressor duty cycle, atomization of gas in expansion tube and temperature of evaporator.
You might have some unusual temperatures where you live and might be OK to do AC work (where I am it's 85+). But if you're in the 60 or less, AC work changes a bit. The only way you really know how much Freon is in a system is from a fresh refill.
I have run on a bit but I hope some of this helps explaining principals.
Thread Starter
Instructor
Joined: Oct 2002
Posts: 218
Likes: 4
From: Durham NC
Do you have a set of gauges now?
The pressures of an AC system while operating are always moving up and down. It never really stays in one place. As the pressure in the low side reaches 22 psi the switch opens and the compressor stops. The pressure then starts to rise to about 46 psi where the cycling switch then closes and the compressor starts and the whole cycle starts again.
Freon is not like air. For a given temperature there is a given pressure. That’s why there is a pressure chart for all refrigeration gases. It's not like putting air in a tire where the pressure goes down when air is removed. That’s why the static pressure in a system is dependent on the ambient temperature around it.
Removing gas is not what you really want to do as you will not really see a change in pressure. You could end up with pipes freezing over. But what it will affect is how the whole system operates, compressor duty cycle, atomization of gas in expansion tube and temperature of evaporator.
You might have some unusual temperatures where you live and might be OK to do AC work (where I am it's 85+). But if you're in the 60 or less, AC work changes a bit. The only way you really know how much Freon is in a system is from a fresh refill.
I have run on a bit but I hope some of this helps explaining principals.
The pressures of an AC system while operating are always moving up and down. It never really stays in one place. As the pressure in the low side reaches 22 psi the switch opens and the compressor stops. The pressure then starts to rise to about 46 psi where the cycling switch then closes and the compressor starts and the whole cycle starts again.
Freon is not like air. For a given temperature there is a given pressure. That’s why there is a pressure chart for all refrigeration gases. It's not like putting air in a tire where the pressure goes down when air is removed. That’s why the static pressure in a system is dependent on the ambient temperature around it.
Removing gas is not what you really want to do as you will not really see a change in pressure. You could end up with pipes freezing over. But what it will affect is how the whole system operates, compressor duty cycle, atomization of gas in expansion tube and temperature of evaporator.
You might have some unusual temperatures where you live and might be OK to do AC work (where I am it's 85+). But if you're in the 60 or less, AC work changes a bit. The only way you really know how much Freon is in a system is from a fresh refill.
I have run on a bit but I hope some of this helps explaining principals.
Thanks. Great information. It is over 75 degrees here today.