AC turns on 1 sec then off. Full charge [Resolved, bad high pressure switch]

[Brickbox8398]

I’ve had this car for 6 months. Gave it a new life after being unregistered for 6 years and repaired all the typical and major things that go wrong on p80s. Finally getting around to the AC and here is my situation. AC flexible lines and a rotten drier were obvious replacements. Also did the condensor. I put in a couple ounces of pag46 kind of assuming that was what I needed. Hooked up a manifold gage set and pulled vacuum. It held vacuum. So I think I replaced everything that needed it. Evaporator seems to have held up. I turned on the AC and gave it the first 12 oz can of 134. Near the end of that can the cooling fan went into high and the compressor clicked on for a second then clicked off. I figured this was a good sign and the compressor would start cycling more as I entered the 2nd can but nothing changed after this. It appears this system wants 26 oz, and given I put in 24 I would have thought to have more cycling by now. I ended up putting 3 cans in which seems like too much but still nothing changed. Cooling fan on high. No AC cycling. I’m reading 80 psi with compressor not on, at 60F ambient.

From here I jumped the relay to force the compressor on so I can get a charge pressure and I’m reading 32 psi. This seems like a pretty good place to be. But the compressor doesn’t want to stay on naturally with the relay installed. It still only clicks on for 1 sec and only after turning off the car then on again. If I unplug the low pressure sensor the cooling/rad fan will turn off. Jump these pins or replace connector and it will turn back to high but not cycle the compressor. If I unplug the high sensor the cooling fan slows down. Plug it back in and the compressor cycles for 1 sec and the cooling fan goes back to high.

Not sure what to do here. Logic says I overcharged the system at 36 oz give or take but 32 psi says otherwise. I kept charging past 2 cans because the compressor never started to cycle. I assume the relay is not the problem because it does cycle the compressor on for 1 sec. I will say that it took about an hour to feed her 3 cans also with periodioc dunking the can into a bucket of hot water. In my research I have seen a few people with a similar situation but no resolution. Seems to be an electrical gremlin.

[Chuck W]

What ECU is in the car? Has it been modified in any way? Had the ECC module in the dash been replaced?

[misha]

When you replace any ac component...in your case dryer & condenser...a proper amount of PAG oil MUST be added.
It can be done separately by adding oil directly to new components or via professional ac machine along with gas.

Then...when system is properly vacuumed and filled with oil and gas...you need to start the car with dials on full cold and blower on high for a few minutes and to watch pressure on gauge.

If you add more oil & gas than needed...the system will be overfilled and low & high pressure sensors will cut the system off.

Components can easily be overfilled with oil because if you even add a proper amount...there will still be some of old oil left in pipes...and system will be overcharged.

[abscate]

You need to monitor both low and high side pressures while filling. I suspect Misha got it right above, you are getting high pressure cutoff.

Is this a 1998 model?

[Brickbox8398]

You need to monitor both low and high side pressures while filling. I suspect Misha got it right above, you are getting high pressure cutoff.

Is this a 1998 model?

Yes its a 98. Its too bad they don't give us a high pressure port to plug my manifold into like every other make and model car. I feel like I am only getting half the story at the low port. I checked my clutch gap and its .8 mm. Supposed to be .3 right? "Check your gap" is a very common result when I search for P80 AC issues...I have my doubts but I guess I can start by shimming that. I suppose it makes sense that the magnetic field is strong enough for an initial "click" to engage, but loses its "grip" thereafter.

[misha]

You need to monitor both low and high side pressures while filling. I suspect Misha got it right above, you are getting high pressure cutoff.

Is this a 1998 model?

No high side port on these.
Low port is for everything...vacuuming,filling and pressure reading.

[misha]

0.8mm is too high.
Spec is 0.3-0.5mm.

[Chuck W]

I made a post on this, but it seems to have disappeared.

That 0.8mm is too much gap. It would not cause a flag in the system and not allow it to engage again until after the car is started, though. Hitting the high-pressure cutoff would, however. You probably ran into an intersection of both of those problems.

You're a good 8-10oz too full on refrigerant, so you need to remedy that.


(The questions on the ECU and ECC were related to an issue we had on our '97GLT, but not applicable here, as you have a 98MY car)

[Brickbox8398]

Just as I thought the clutch gap was not the problem. Shimmed it and still clicks on for 1 sec. In obd850 there is an “ac pressure” readout. Doesn’t explain if it’s high or low, lol. But anyway it read 3078 to 3092 kpa. That is 450 psi…and it didn’t change when I jumped the compressor. Assuming this is the high pressure reading, seems like I should purge some charge and see if it allows the compressor to stay on? I just don’t understand how my low pressure reading doesn’t indicate overcharging. Jumping the compressor yields 32 psi.

[Brickbox8398]

I purged some charge and I seem to get 25-28psi low port when jumping compressor. The high(?) press readout on obd850 did not change before and after purge. Unplugging the high press sensor turns down the cooling fan and clicks the compressor once. During this time obd850 says 14kpa. Not sure what that means. Again unplugging the low press sensor doesn’t do anything and I’m not sure what this means