I have put 1 can of stop leak and 3 cans of 134a into my 99 Silverado extended cab. I hear the click from the compressor but don't know if it clicks back off or what the issue is. The air is still just hot and none of the cans ever got cold when putting them in.

From the start it's been the same, I start a new can and the gauge shoots to red before it soon goes very low between 0 and 10 where it stays until I release and repeat. If I do this often enough the gauge will stay for a while in the green area but then, returns after 30 or so seconds to the same position between 0 and 10.

My first can was the red stop leak stuff and I don't see any leaks. (Threw the can away before I checked if It's black light dye but didn't see any with the black light either anyway.)

I pressed both nozzles for the High and low sides of the system and there is pressure. A lot on the high side.

I took the plug out of the socket on the dryer (just below the low side nozzel.) and put a paper clip into it to jump the circuit but it makes the same click as though the compressor is coming on. The same as when it is just plugged in so it probably doesn't matter.

There is a "Mystery" plug right by the one that goes into the dryer. It is coming from the same grouping of wires. I don't see any possible place for it to be plugged into as the only thing that it would reach to is the dryer but with the car off the thing didn't fit into it. If someone knows or can go look at theirs for me this could solve it. IDK

If your able to give me some insight on the readings from the gauges or help figure out the reason for the "mystery" plug... thanks in advance.

I'm not sure why it is always on red with the trigger NOT pressed and then goes down so low when it is pressed. I checked the fuse and it's good. Maybe I should look to something else or just add more cans?

 

I just bought a '00 Silverado LT to run errands in. My AC works real good for 10-20 minutes and then blows warm air for 5-10 minutes and starts cooling again. I just had it evacuated and a 30 minute vacuum pulled and refilled (added about .5 lbs) and still have the same issue.

I also found the additional weatherhead plug and couldn't find anywhere for it to plug into. So maybe someone will chime in. All I can figure is it was for a option that didn't come with mine.

 

Yes, I hope somebody who knows about the ac in these can help us out. It's good to know you have the same extra plug though. Chances are that it's normal then. I'm not sure about the readings on the gauges still either.

 

I bought a 2000 sierra and have noticed the same thing. A/C ice cold for 15min then the compressor shuts off for an extended time. this seemed to occur on hot days. I also have notice the second connector at the accumulator but was not sure what it was for.


I evacuated the system, put the proper charge into the system and noticed the same problem occurring. I then monitored the high and low side pressures; running the engine at idle for 20mins. The fault never occurred. The system ran perfectly and the compressor never shut off. there was proper cold and hot separation when feeling the lines at either side of the fixed orfice. The cooling system is running perfectly and the fan shroud is in place. No obstructions are present in the condenser fins. I however did notice the low side pressure creeping up slowly from 30 to 40 psi.



I am thinking the system pressure is getting to high and cutting off power to the compressor. When I get the problem occurring again I will either hook up the gauges and monitor the pressure or spray some cold water on the condenser to see if it will drop the pressure enough to start the compressor. I may just swap out the pressure sensor and see what happens.


Some people on other forums are saying this is normally operation but I do not believe it. mY 2000 m/c probably had the same controls and never acted like this.

 

My mechanic checked mine out and said my compressor clutch was slipping. Since it had 196k miles on it I opted to replace the compressor, accumulator and orifice tube and be done with it.

As far as the extra plug I'm wondering if this harness was also used for the Suburbans and was for the auxiliary AC in the rear passenger compartment.

 

Look closely at the plug, if it is clean inside at the terminals that means it was plugged in on your truck, if there is signs of corrosion then just leave it hanging.

Also, can you show us the mystery plug, just played that game my self, I might be able to point you in the right direction. It is unlikely that your harness was shared in the suburbans and tahoes in 99. 99 was a crotch year where only the Silverado was updated to the GMT-800 platform, K-series trucks, suburbans and tahoes remained on the GMT-400 platform and was very different.

 

I did find spec's for the a/c compressor controls.
the low side pressure cycling switch with cut out below 18psi and cut out above 45psi
the high side pressure cut out switch will cut out when high side pressures go above 420psi


my high side pressures never went above 190psi iirc. the low side was up at 40psi. I think on hot days the low side pressure is going over the 45psi limit. I think this may be due to poor air flow through the condenser. I am going to try to wash out the condenser fins and see if there is any improvement.

I still haven't identified the mystery connector at the accumulator. the wiring schematics show nothing a/c related being there. Maybe its for another none a/c related option on fully loaded models.

 

Be careful screwing the "dust cap" back on. I swear mine might be cross threaded
on my LT1 f-body.

Are you shaking the can and turning it between 12 and 3pm, waiting 3 seconds or so?

 

I have access to a robinair a/c machine with manifold gauges.

 

As far as this goes, we really are going to need a picture of it. When I dropped a new motor into my truck I had to play the Mystery plug ID game as well. When I figured out what some of them were I could not figure out why they were where they were. For example I had a flat 4 prong male plug sticking up at the back of the intake right next to the distributor, turns out it was supposed to go down below and had absolutely nothing to do with the top of the motor but none the less did in fact belong to my truck. That said this plug might just be somewhere it's not supposed to be and is misleading the OP and subsequently those who try to help with it.