1978 AC Temperature Cutout Switch

[1978L48jafo]

Does anyone know how the capillary tube on the temperature cutout switch is installed ( position, number of wraps e.g.). The service manual says to put it back the same was as the old. Unfortunately mine was missing. My understanding is that it turns off the compressor to prevent the system from freezing up??? And it and the tube with the orifice should be covered by insulation. Any help is appreciated my AC has never worked very well.
John

 

[black_81_vette]

I would look at the low side suction line by the evaperator box right under the fiting is a filter. a restriction by contamination will kill a/c performance the capillary tube would be a rare falure in my opinion.

 

[photovette]

The capillary tube end should be clipped to the tube where it exists the evaporator coil but inside the a/c housing--not where it exits out into the engine compartment. It does not need to be insulated. It shuts off the compressor at 34F coil temperature to prevent frost formation.

 

[1978L48jafo]

Thanks I replaced last year when I switched over to 134. Didn't seem very dirty but it was cheap so I just replaced it. Besides I read somewhere that any time you open the system it should be replaced.

I would look at the low side suction line by the evaperator box right under the fiting is a filter. a restriction by contamination will kill a/c performance the capillary tube would be a rare falure in my opinion.

 

[1978L48jafo]

photovette
I have the capillary tube tie wrapped to the vertical tube with the orface installed in it. Is this incorrect? It's causing the compressor to cycle quite a bit.

The gm service manual says the pipe with the attached capillary tube should be insulated but it doesn't exactly list where to place the tube. I will take a look at the housing tomorrow for a likely spot for this sensor. If anyone has a drawing or photo showing this setup it would be appreciated.

The capillary tube end should be clipped to the tube where it exists the evaporator coil but inside the a/c housing--not where it exits out into the engine compartment. It does not need to be insulated. It shuts off the compressor at 34F coil temperature to prevent frost formation.

 

[wishuwerehere82]

Generally those tubes were hose clamped to the evaporator line and covered with that black modelling clay. it should be a straight run down the side of the line for the tube to make intimate contact with the evap. line.

 

[1978L48jafo]

So the line is clamped to the metal tube (Evaporator Line), I tied to move the line to the inside of the box and it is actually working worse at the moment. Is the clay or dumb dumb important for it to work properly I covered mine with a piece of pipe insolution and duct taped the seam.
Thanks
John

Generally those tubes were hose clamped to the evaporator line and covered with that black modelling clay. it should be a straight run down the side of the line for the tube to make intimate contact with the evap. line.

 

[wishuwerehere82]

As long as the tip of the pipe is inside an insulated part of the line, it should be accurate. It is important that the part of the line that contacts it is covered, otherwise it will give a false reading on the temp of the evap. coil.

 

[1978L48jafo]

Thanks Pete,
The evaporator tube gets super cold really quick and I would estimate the compressor cycles in the garage every few minutes (3 minutes). I rebuilt the box and controls last year with a kit from dr rebuild and I installed a oversized blower and cage. After all of this the system just sort of works, chilled air not cold by any streach.

To be honest I just put in the Envirosafe R114 thinking the 134 was the problem and it's is not working any better. I just installed two shut off valves. No improvement there either.
I am open to suggestions

As long as the tip of the pipe is inside an insulated part of the line, it should be accurate. It is important that the part of the line that contacts it is covered, otherwise it will give a false reading on the temp of the evap. coil.

 

[wishuwerehere82]

3 minutes seems kind of a long time for tyhe compressor to run as it's cooling down. Apparently, your coils are not getting cold enough for the amount of air flow you put through them.

You might try putting a little more freon in the system until the compressor cycles every 5-10 seconds at idle.

Ideally, the compressor should run long enough to fill the accumulator with liquid freon and then flow into the evap. coils. At that point, the compressor will turn off until the accumulator empties and the pressure goes low. As long as you are drawing heat off the coil at a higher rate than the coil can dissipate, the freon pressure will stay low indicating that you are pumping more gas than liquid, and the compressor will stay on.

 

[1978L48jafo]

Thanks I will give this a try after work, I don't own a gage set(to check the high side). I just have a gage to plug into the low side. I will add another can and see what happens.

On this system I don't see an actual accumulator are you referring to refrigerant volume in the evaporator. I am asking because I purchased the vet with the AC system cannibalized, so it is possible I missed something although not according to the assembly manual??????

Just a thought, the receiver drier is an autozone replacement part, is there any chance my cheapness a few years back is the cause of all this grief?????

anyway I will add in more freon this evening and see what this does....

Thanks for you help
John

3 minutes seems kind of a long time for tyhe compressor to run as it's cooling down. Apparently, your coils are not getting cold enough for the amount of air flow you put through them.

You might try putting a little more freon in the system until the compressor cycles every 5-10 seconds at idle.

Ideally, the compressor should run long enough to fill the accumulator with liquid freon and then flow into the evap. coils. At that point, the compressor will turn off until the accumulator empties and the pressure goes low. As long as you are drawing heat off the coil at a higher rate than the coil can dissipate, the freon pressure will stay low indicating that you are pumping more gas than liquid, and the compressor will stay on.

 

[wishuwerehere82]

Sorry,

I meant the receiver/dryer.

 

[1978L48jafo]

Adjustable Expansion Valve

No criticism intended, was looking over some parts online at Autozone and they call it an accumulator too. I just wanted to make sure I understood.....

They are now listing an adjustable expansion valve for the C3s. Does anyone have an opinion whether this would be effective upgrade? I would imagine it has a probe that would go inside the case near or attached to the cooling coils.

I located an angled R134 fitting, my fitting at the compressor is near impossible to get an anything to attach, need to unbolt the compressor and take off the belt every time I do anything with the air.
John

Sorry,

I meant the receiver/dryer.

 

[wishuwerehere82]

John,
I'm not sure we are talking about the same thing.
The accumulator/receiver/dryer is a large silver cannister that is located right in front of your heater box,where the return line (Large Diameter foam insulated hose)for the compressor connects to a fitting that goes into the bottom of it. it is the low pressure side of the compressor where the freon gas returns to the compressor.
Maybe you didn't put one in the system?
It should have a fitting on the side of the cannister, which is where you will add freon.

DO NOT connect to the fitting at the compressor,that is the high pressure line and can cause the can to explode in your hand.

The location of your temp. sensor pipe should be on the small diameter line that runs down the front of the heater box just as it exits the box. It should have some black tar putty around it for insulation. That line runs forward to the condensor coil in front if the radiator.
DOES ANYONE HAVE A PICTURE OF A '78 A/C SYSTEM THAT WE CAN SHARE?

 

[wishuwerehere82]

John,
I'm going to try to look at a 78 that my friend has, just to make sure i know where all the components are located.
If I can get some photo's, I will send them to you via E-mail,
as I have no way to attach pix to the action center postings.

 

[1978L48jafo]

Yes of course I have a receiver drier installed the fittings are near impossible to reach. I am considering making a small acess panel Are you sure the fitting on the back of the AC compressor lines is a high pressure line? This would certainly explain a lot I have gone through the assembly manual without any success, I am going out not to get my service manuals... I won't do any thing else until I sort this out.
Thanks

John,
I'm not sure we are talking about the same thing.
The accumulator/receiver/dryer is a large silver cannister that is located right in front of your heater box,where the return line (Large Diameter foam insulated hose)for the compressor connects to a fitting that goes into the bottom of it. it is the low pressure side of the compressor where the freon gas returns to the compressor.
Maybe you didn't put one in the system?
It should have a fitting on the side of the cannister, which is where you will add freon.

DO NOT connect to the fitting at the compressor,that is the high pressure line and can cause the can to explode in your hand.

The location of your temp. sensor pipe should be on the small diameter line that runs down the front of the heater box just as it exits the box. It should have some black tar putty around it for insulation. That line runs forward to the condensor coil in front if the radiator.
DOES ANYONE HAVE A PICTURE OF A '78 A/C SYSTEM THAT WE CAN SHARE?

 

[wishuwerehere82]

Sorry I can't be of more help, but I'm sure my '82 is different than the '78. In general, the low pressure filling fitting is on the large diameter lines. The fittings on my '82 are located next to each other by the fender, and the receiver is under the fender. The filling valve is a larger diameter than the high pressure one so you can't switch them by mistake. I can't see where the sensor goes into the box at all. Also, my friends '78 doesn't have A/C so I guess I can't get any photo's.

 

[1978L48jafo]

No problem I just checked and the fitting behind the compressor is tapped into the large or low side line. Appreciate the help calling it a night. Tomorrow I will start over and see what I have.

John,
I'm going to try to look at a 78 that my friend has, just to make sure i know where all the components are located.
If I can get some photo's, I will send them to you via E-mail,
as I have no way to attach pix to the action center postings.

 

[curtis]

Here is something I got from Bossvette for pictures.

To post pictures so they show up in your post first you need to have the pictures on the web I use a photo hosting service:
http://www.villagephotos.com/index.asp
is one of many. Click on the IMG button in the area above where you type your posting Then you copy the URL of the photo to the Dialog box (be sure there is only one http) by using the links under the photos in blue, just click where it says "copy URL to clipboard" in blue.
Your picture should show up in your post

I might have done it wrong, but the picture I set up does'nt appear on the screen until you click the link for it.

 

[1978L48jafo]

Question for the AC experts.

Question for the AC experts. Should the low pressure side reading be taken while the compressor is idling or running? My low side pressure right now is above 50 with the compressor is not running and then drops to about 25 or slightly lower when it kicks in. Working pretty well right now but I don't want to leave in a overcharged condition.