C2 C-60 functional and service questions
From information I have reviewed there is no high pressure compressor cutoff switch, so the compressor is on all the time when the AC control knob is pulled out. That seems odd. All modern AC systems I'm familiar with have a high pressure cutoff switch, which is why the compressor cycles on and off. Is there some kind of overpressure relief device in the compressor or otherwise how is system pressure controlled? Second question: according to the AIM it appears that the evaporator case was assembled including the blower motor when it arrived at the plant and the assembly was bolted to the dash on the assembly line. It's not clear from the AIM or looking at a C-60 car how the blower motor is attached to the evaporator case. Does anyone know? Third question: Can the motor be removed from the car separately or does the whole evaporator case have to come out to access the motor for overhaul?
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Re: C2 C-60 functional and service questions
Duke,
Last question is yes the motor will come off separately.
First Question: The single pole switch (if that's the one you are asking about) on the back plate, is a clutch cut out switch that is temp related to protect the compressor from overheat. Then the back plate has the over pressure valve which is a over pressure blow off to protect the system from blowing up. That pressure valve has a 440 on it that I think is the pressure it is set at.
Dom -
Re: C2 C-60 functional and service questions
The blower motor is attached to the evap case with sheet metal screws and as you probably know has a capacitor under one screw and a ground under another.
DomComment
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Re: C2 C-60 functional and service questions
Duke ,
you got me thinking about the pressure, and I know this question has come up. My best guess is that the system is a sealed system with a standing pressure when off. That being said then there is nothing that can raise the pressure unless it gets it from an outside source, which is not possible. Then controlling the pressure would be done when charging the system (hi & low pressure) and be affected by temp a bit. RPM's? I think the expansion valve is limited to how much will pass thru it which limits the pressure given to the low side limiting what is blown into the cylinders, which in turn will lower what comes out the hi side.
There are pro's here that know much more than I, but the cycling switch on later cars (to my best knowledge) that turns the compressor on & off, is controlled by temp to keep the evaporator from icing up.
A bit of info for those that might be interested is that no C2's came with a clutch cut out switch on the back plate.
DomComment
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Re: C2 C-60 functional and service questions
Thanks for the responses, Dom. By "backplate" do you mean the rear of the compressor? I have a '74 Vega shop manual that has a good AC section, and I think the basic architecture and compressor is the same as sixties vintage systems. It states that there is a thermal switch that controls compressor engagement, and the rear face of the compressor has a mechanical overpressure relieve valve, which is a safety device if the system develops too much pressure. If it opens, freon will escape to the atmosphere. It looks like removing the blower motor and getting it out between the fender and evap case is tricky. Do you have any hints? In the meantime I'm going to do some more research in my available documentation. DukeComment
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Re: C2 C-60 functional and service questions
Duke,
Your right, The back the plate on the back with the blow valve and the clutch cut out thermal swich with 1 prong.
Blower motor I was refering to was a C2. Suggestion is don't cuss to loud.
Your compressor date code is under the inlet & outlet manifold that has the one 19/16 head bolt to secure it. A being Jan, and the I is used in the alphebet with compressors. Your foil code will have the completion date of the compressor (all in numbers with a 1,2,opossibly 3 following the numerical code.
31462= march 14, 1966, shift 2 incase you didn;t have that info.
Dom 1Comment
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Re: C2 C-60 functional and service questions
Considering that the AIM shows the evaporator and blower motor installed together as a unit, is it possible to remove just the blower while the evaporator remains in the car, and if so, how difficult would that be? It seems access to the fasteners would be awkward at best.Comment
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Re: C2 C-60 functional and service questions
Hi Duke:
My '67 small block has factory A/C, and I rebuilt the whole system a few years ago. As I recall, the blower motor can be easily removed while the evaporator case remains in the car. The really awful job is removing and reinstalling the evaporator case. That is one of the most tedious jobs I have ever done on my '67. Access to many of the screws involved was very difficult.
Regarding the compressor controls, the C2 A/C systems ran the compressor continuously whenever the A/C was on. Regulation of the evaporator temperature was accomplished by carefully managing the pressure in the evaporator using a continuous analog control loop. In 1967 this was done with a POA valve, but in earlier C2 years it was done with an STV valve. Loosely speaking, I think that any un-needed refrigerant effectively bypassed the evaporator and was not used.
To my knowledge, the 1967 system has no provisions for an over-pressure cutout or an under-pressure cutout. Whenever the A/C control is turned on, the compressor runs, period.
In later years (some time in the 1970s) the control system was simplified to a simple on-off control similar to a household furnace thermostat. This system monitored the evaporator temperature and cycled the compressor on and off to keep the evaporator temperature within a target range (just above freezing). This type of control system is the one that cycles the compressor on and off while the A/C is on. In theory, such a system is more energy efficient, since the compressor does not run continuously.
I believe these newer systems also incorporated some cutouts to prevent damage to the system from over-pressure or under-pressure. These things seem like a good idea, but I don't think they were included in the C2 systems.Comment
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Re: C2 C-60 functional and service questions
Joe,
I did the NCRS no no back in 1971 when I bought a wrecked 67 BB 435. I was a Chevy mechanic in CA and I decided to add AC that was not available on the 435 HP. Can get hot in CA. The car only had left front damage, but was ran hard. I paid a whopping 550.00 for it. The service writer talked me into replacing the whole front end which was a mistake with the amount of damage to the left front.
Now back to the thread. I liked your info, and I cheated and did my box with the engine out and front end off. The box was still bear and there was some cutting to do switching from the original heater box to the AC box. I replaced the blower motor back in the 70's and think I used the blower motor that was on the heater box. As I remember the AC blower motor was a bit longer than the non AC blower motor, so mine looks easy to remove.
You are right about the pressure cut out, there were none on C2's. Now I think the replacement POA valves come with wiring that does the pressure cut out. I noticed a thermo sensor that is on the aluminum line that brings the cold gas to the evaporator. The one that is under the tape. Seems that it might regulate the expansion valve.
I wouldn't want a cycling switch on a A6 compressor, even with the rubber damper on the hub clutch. I mentioned this in another thread, but I engage the AC at a low RPM to keep the clutch alive that is a metal to metal clutch. Cycling a A6 would shorten its life, especially at highway speeds. Saw sparks come from a clutch while working on a later car with the A6. The engine was at about 3800 when the compressor engaged and
you could see tiny sparks come from the clutch. It may have been caused because of a freshly machined clutch that was not worn in, but from that day on I was anal and would only engage at a lower RPM.
DomComment
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Re: C2 C-60 functional and service questions
The C2 A/C control systems are designed to run the compressor continuously, with the control system continuously managing the refrigerant flow through the evaporator to maintain the temperature at just above 32 degrees F. The primary device that manages this is the STV valve for '63-'66, and the "improved" POA valve for '67. As I recall, both of these also connect to the expansion valve (the one with the sensing bulb under the asphalt tape at the evaporator exit), so the interaction between the two is complex.
I have read a lot about how the STV/POA and expansion valve work together to manage the evaporator temperature, but it's hard to get a complete picture. The bottom line, though, is that when everything is working properly, the evaporator temperature is continuously maintained at just above 32 degrees F.
BTW, as far as I can tell, the improvement provided by the POA valve was better ability to respond to atmospheric pressure differences due to different elevations above sea level. Unfortunately, the resulting POA valve is more complicated than an STV valve and is not designed to be serviceable, while the earlier STV valve can be disassembled and rebuilt.
Overall, I think the newer cycling systems are far simpler to understand and easier to service. They simply turn the compressor on and off to maintain the evaporator temperature within a narrow range (say, 32 to 38 degrees F). This is what the "POA elimination valve" does for a system that was designed to use a POA valve. My main concern about this change is the same as yours, that the original compressor clutch was not designed to be cycled on and off. However, many people have made this change and I have not heard complaints about premature clutch failures.Comment
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Re: C2 C-60 functional and service questions
Call me crazy, but I prefer to only engage.or disengage A/C at idle RPM or just above.Comment
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Re: C2 C-60 functional and service questions
On the c2 compressor, is there not a green wire coming from the the right side terminal connection attaching to a fin on the evaporator for the purpose of regulating the compressor?Comment
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Re: C2 C-60 functional and service questions
I'm away from home right now, but I recall that there is a single green wire that goes to the compressor, and the purpose of this wire is to activate the compressor clutch. As far as I know, that wire has 12V on it whenever the A/C has been turned on by the user. I don't think there is anything that would cause the compressor to cycle when the A/C is on.Comment
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