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Discussion Starter · #1 ·
Charging a discharged system on a 90q20v

Pulled vacuum on the system and bought 4 cans of R12 for a small fortune.

I put the first two in with the car running and AC on with a direct charging hose. It was still blowing warm so I looked up the specs and realized I needed 37 oz. of refridgerant. So I ordered 2 more cans (I had 2 initially), and this time I hooked up a r134a gauge manifold with a R12 -> R134a hose to hook the can up to the manifold.

I also noticed that with the red plug disconnected on the high side, the ac compressor did not run, so I ended up putting most of the third can in without the comrpessor running. I figured this out and disconnected the high side and hooked the red plug back up and the compressor started running again. But the compressor on this car runs weird, it kicks on every few seconds for a second or so. I could watch this on the low side guage. The pressure would read 20 psi, the compressor would kick in, you could see the clutch spin, and the pressure would climb to 50 psi over a few seconds, the the compressor would shut off and the clutch would stop spinning.

I finished putting the third can in (with only the low side connected from the manifold this time) and it started blowing cold/cool, but not as cold as I expected. I then punctured the fourth can, and started putting it in, but stopped after a few oz. because with the low side readings bouncing up and down as the clutch went in and out, I couldn't figure out how I was supposed to tell when I was done.

So here i am.

First of all, what's the PSI I should be charging to on this car? I can't find this information anywhere. Either high side, low side, or both preferably.

Second, now that it's blowing cool/cold-ish, it's only doing so out of the center vents. The side vents are blowing warm and it's highly annoying. Any idea why it's doing this? I rebuilt the heater box a few years ago with new foam -- maybe i covered up something I wasn't supposed to? the car has pretty much been sitting since then as i have R&Rs the engine and interior. Any quick way to diagnose this? Would really not like to take the dash apart again to get to the blower box.

Thanks!
 

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hmmm. red plug would be the high pressure cut off switch. unplugging that kills power to the clutch...leave it plugged in.
cool air in center vent only points to issue with doors in the hvac system not working properly.
Ac pressure should be around 190-200 with R12 on the high side and around 15-20 on the low side with a proper charge. If pressure is bouncing around it could mean the compressor is bad.
With the ac on the low side should drop in pressure (to no lower than 10psi) and the hight side should rise(not go higher than about 210). Anything else means component problems.
 

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If you're not using a recirculating shop machine, only charge through the low side - black cap - nearest to or on the compressor.

Leave everything else plugged in and turn the system on full/high. Fill in spurts cuz It will take a while when filling for the compressor to cycle the refrigerant through, so the pressure will spike and fall several times. This is the manifold pressure at the pump and not the sytem pressure. Just fill a little, stop then fill some more. Once the compressor is on 100% of the time, you are reading low side system pressure.

I'm used to r134, but that is 40 psi LS fill at 75 degrees with the compressor on. No number means anything with compressor off.

Instead of r12, I would have used a product called envirosafe. it's isobutane and safer than r134 and dirt cheap except for the hazmat shipping. I have put it directly into several r12 systems and it's colder that a witches tit. Compataible with any oil and o-ring material so you don't have to crack the system and replace all the o-rings. It has tended to make a whistling noise in the orifice, however. I never heard back from the manufacturer on why. But, they run that stuff all over the South and in South America.

Anybody who says it's a fire hazard is not thinking. What do you think gasoline is?

If some vents are truly cold, and some are warm, you might have to pull the dash - should replace the heater core anyway. With luck you have a vaccum leak somewhere NOT behind the dash, lol.
 

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Discussion Starter · #4 ·
So you're saying that the compressor coming on and off and spiking and dropping the pressure every few seconds is normal? And that I should keep charging until the compressor stays on all the time? I have no idea how to read the pressure while I'm charging in that case. Or does this truly mean it's a bad compressor as the previous poster suggested?

The heater core was replaced when I rebuilt the heater box, so it's new. I guess it's a vacuum leak or something causing the flaps to not open.
 

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No, it's not normal. Usually filling from the low side, you get nothing for a long time, then the compressor kicks on and stays on. Before you start considering the compressor, I would check the clutch relay and the pressure switch. Is the electric fan running the entire time?

If you have access to a proper manifold gauge set, you could jump the clutch to +12v and watch the gauges while you recharge for signs of something being out of whack. That's the only safe way to bypass the switch.

Check the hard black plastic vacuum line that runs through the firewall to the engine. Make sure you have a vac check valve on it, and make sure it's oriented correctly. If you have a my-t-vac you can pull a vacuum on the line to the hvac box and see if it holds.

Last question - when you rebuilt the hvac box, did you replace the drier and the expansion valve?
 

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Oh, and check to make sure your recirculation flap functions. Luckily the vac servo for that is easy to access.
 

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9020V said:
So you're saying that the compressor coming on and off and spiking and dropping the pressure every few seconds is normal? And that I should keep charging until the compressor stays on all the time? I have no idea how to read the pressure while I'm charging in that case. Or does this truly mean it's a bad compressor as the previous poster suggested?

The heater core was replaced when I rebuilt the heater box, so it's new. I guess it's a vacuum leak or something causing the flaps to not open.
Only for the first minute of charging from flat. After that, the compressor should stay on but the pressure will still not be stable until the fill works its way through.

I find that it works best blipping in some fill, waiting for 30 seconds, then filling more, etc. When I worked at a shop, we had a big machine that you just hooked up and hit the green button :p Too easy.

it's tricky charging with just a can, but a fill hose with a guage on it is pretty cheap.

On the vent problem, you might not have hooked something back up correctly or something could have cracked. The 90 dashboard removal is bordering on inhuman torture.

I would create a different topic with that in the headline (cold center, warm sides) and somebody might recognize it and know the exact dingus or doohicky that causes it.
 
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