I have an 85' 4+3 with 62,000 miles on it. I did a search and couldn't find what I was looking for. I hope someone can help.

I just put in a new AC Compresser and Accumulator and I was trying to get every working so I could have the A\C working since it's starting to get hot here in Michigan.

The problem I'm having is the A\C Clutch isn't engaging fully. It will come on a few seconds then it shuts itself off. It will do this sporadically but it will never fully engage. The system has a charge it's just not fully charged. I can bypass the switch and if I give it a constant 12V right from the battery it will engage perfectly. I also tried an A\C Compressor Clutch tool to tighten the nut down on the clutch to see if it was maybe too far out to fully engage and that didn't work either.

Anyone have any ideas?

Thanks!

 

The system has a pressure switch on it which will not allow the ac clutch to stay engaged UNLESS you have a full charge of freon--I usually jump the connector at the pressure switch while charging the system--however --I do not know where the switch is located on your car --since you say you can jump directly to the clutch and it works--I'd do that and add the correct amount of freon and then check how the system works---you may have other issues BUT I'd start with the correct amount of freon first and go from there and don't forget to add AC oil to the system or the compressor will have a short life. Good Luck.

 

It sounds like your low pressure switch is working perfectly.

 

..one of the first questions i would ask is did you evacuate (pump down) the system...if ya didn't ya got problems!...ssuming you did the install correctly, it would, on it's face (the symptoms), seem to indicate that you do NOT have enough refrigerant in the system...the low presor switch is in part, there to protect the compressor from low charge and freeze-up.....

..if you start car and turn the ac on to "max" and the compressor clutch is cycling, remove the sensor connector from the large suction line of the ac..then, get a piece of wire and short the contacts therein...you compressor's clutch should pull in and stay in (on)....if it doesn't you either have a broken wire some place, or, the compressors' clutch is defective.....i know that some of this info is beyond the scope of what you asked.....are youusing a set of refrigeration gauges?

 

Do you remember what you put in the 'search' bar?

Because I just posted with pics an A/C diagnostics/re-charge thread about 2 weeks ago.

 

And just don't jumper that switch for too long - a low charge can't carry the oil it needs to lubricate the compressor (that's one of the reason the engineers put in the switch). In fact, I wouldn't jumper it until you're putting in the balance of the charge. Also, disconnect the fan switch on the High Pressure line. That'll keep the main fan running while you're charging it - forget sticking a fan a fan in front of it - that just doesn't work on a bottom feeder like the Vette.

 

Thanks everyone! I'll do what you guys recommended and try jumpering the switch and double checking my R134A levels.

SCHRADE - I don't recall what I put in the search but I'll also look at your post and see if something in there helps me.

Thanks again! I'll let you guys know how it goes!

 

Like suncr said above you, do NOT let the compressor run more than a few seconds with the low pressure switch jumped...

 

OK, so I checked the pressure on the low side of the accumulator and with the MOTOR OFF I have adaquate pressure right up to the blue line on my pressure gauge.

However, when the motor is running and I have the clutch jumpered and engaged the pressure is barely in the blue, indicating an inadaquate charge.

Should I be trying to get a full charge when the clutch is engaged since that's when the compressor will actually be doing it's job, or is the charge with the motor off what I'm looking for in a good charge?

 

Keep in mind, with the compressor off, the system pressures between the high side and low side balance as the system is static.

Not knowing what type of gauges you are using, the "blue line" is not much help. The ones I use also have a temperature compensation range (a blue band) - I service mine to the mid point of the range. If I remember correctly, I'm running about 55 psi on the low side.

Regardless, you need to charge the system with the compressor running by either adding the proper amount of freon by weight or when topping off the system, to the recommended "operating" pressures.

 

OK, I'll check that out also. I'm pretty sure that there is a pressure reading on it, I just don't remember what it is. I'll find out. Thanks again!

 

"If I remember correctly, I'm running about 55 psi on the low side."

If that's an operating pressure, it wouldn't be making cold air at that pressure (unless it's your house and it's using R22). At 55 psi, R12 is about 60 degrees. Add about 6 degrees for superheat and you'll probably have 70 to 75 degree air out of your center vent.

The Low Pressure Switch opens at 25 psi (R12) and closes at 50 Psi - so your system needs at least 50 psi to engage the clutch. Static pressure is a function of ambient temperature (assuming the engine hasn't warmed anything up), so down to about 53 degrees, even a 1/2 lb of gas will get it running. To keep it running and not have the liquid flash off the minute it hits the Evaporator (taking all the oomph out of it), it's going to need at least 3/4's of it's fill. Get a set of gages that reads pressure - they're cheap enough and you won't have to guess at it. I have no idea how a gage with only a blue line or area could compensate for pressure variations due to temperature. Maybe they tell you to only use it when 70 degrees or better? And if you don't know how much is in it, charge until the high side reads 2.2 to 2.5 times the air across the condensor. That will get you in the ballpark on most charts.

 

I played with it last night and I was able to get the compressor to come on more consistently with more pressure. I had 65PSI in the system with the motor off and with the motor on and the compressor running I had about 40PSI. I couldn't get the compressor to stay on consistently to add a full 55PSI or60PSI, any ideas on an easy way to jumper it?

 

There's another switch - a high pressure cutout on the high pressure line which will open when the pressure gets high enough to blow a hole in the hood. Get some gages before you hurt yourself.

 

Place the can of freon in warm water. (NOT HOT) That will raise the pressure enough to overcome the system enough to complete the charge.

 

UPDATE -

Instead of blowing myself up, I grabbed a set of gauges and started a slow charge of R134A into the system. You were right the guages took all the guess work out of it. I was able to get another full can of R134A into the system within the PSI ratings for my car and system. I'm still a little low and need to pick up another can of R134A but at the point I ran out of it, my vette had COLD air conditioning. I will keep everyone updated as to where I end up.

Thanks again!

 

FINALIZED. I topped off the entire system with R134a and it's colder than a ditch digger's a$$ in the Klondike!

Thank you again for everyone's help!