A/C Woes

[rusty9]

This morning I went to have my a/c system evacuated and recharged, but when I talked to the mechanic he said he converted to r134 and charged the system but couldn't get the compressor to kick on so he thinks there's and electrical issue somewhere. I doubt he did anything besides push the ac button a few times...but the light wouldnt come on.

So I started testing everything and all the connections...relays click and fuses are good. and magically i get a blinking ac light now. sounds like the clutch engages, idles up, light stays lit for a few seconds...struggles...clutch releases, light starts blinking.

ok I says, let me jump the relay to the clutch see what happens. this stalls the engine immediately, same happens if i apply 12v to pin 4 on the compressor connector. lol think the compressor is seized? 3vz btw

[retiredat44]

what's the history of the car and a/c? when was the last time the a/c ran correctly? how and when did it stop running correctly?

[JohnGD]

On manual AC systems the light blinks only when the compressor and engine rpms differ.

If the compressor ran before the mechanic worked on it, it's his fault.

[Stillrunning]

The engine may have stalled because jumping the clutch does not activate the idle up. I'd remove the A/C belt then jump the clutch and try to turn the compressor by hand. If the mechanic converted to 134a why didn't he trace the no compressor on problem? After a system evacuation a proper refrigerant charge would have involved an initial static charge to get enough pressure to prevent the pressure switch from tripping then turning on the A/C and charging to proper pressures. That can't happen without the compressor. I also hope he changed out the filter/dryer. It may have been necessary to use an additive to make the R12 lub oil compatible with R134a and possible the system needed oil added.

[rusty9]

Sorry, the back story is the lines were opened when I swapped engines last year. A/C worked on both mine and donor car. I just put it off getting it recharged since i was living in new york and didn't need the a/c in the fall/winter

The mechanic said he put in a little less than 2lbs, and told me there's an electrical problem since the compressor didn't turn on. but are you saying there's no way to properly charge this system without the compressor running? I'm no expert on a/c systems that's why I took it to an a/c shop. If he just dumped all that refrigerant onto one side, would that cause the compressor to lock up?

[Stillrunning]

Originally Posted by rusty9

The mechanic said he put in a little less than 2lbs

The from empty charge is about 30oz, so he's probably ok on fill volume, but to do this properly he should have run the A/C to check operating pressures and cold air performance and check for leaks.

and told me there's an electrical problem since the compressor didn't turn on.

Why is not being able to diagnose A/C electrical your responsibility, isn't he an A/C tech?

but are you saying there's no way to properly charge this system without the compressor running?

Well, in a way, if not just to check operating pressures. The initial static fill volume gets you close and may be OK, but does not determine operation and final volume to adjust pressures. An A/C shop should especially be able to do this properly.

If he just dumped all that refrigerant onto one side, would that cause the compressor to lock up?

If he evacuated properly with a vacuum pump, which would also show if the system has leaks, then there's negative pressure (compared to atmospheric) in the system. This allows the initial fill without the compressor running. The system pressure should equalize on both sides of the expansion valve and compressor at this initial fill. He should not have attempted to run the compressor at this fill stage as he's adding pure liquid. The system will not turn on initially anyway due to the pressure switch, but you don't want to start it too fast once the pressure reaches switch on level. It's too much liquid too fast when the compressor's running that will cause seals to blow or possible damage to the compressor. DIY'rs really should not fill A/C with can upside down. If you left the system open for any length of time then moisture gets into it. It's possible rust and lack of initial lubricant has killed your compressor. Adding the correct amount of oil volume is an art after the initial dry fill or when replacing components. The FSM gives oil refill amounts depending on component replaced. Obviously rust floating in the system is not good.

I should add that the 30oz is by volume not weight.

Edit2: Sorry, but another afterthought. R134a operates at higher pressures than R12. The 30oz I gave is for 134a in a R134a system. When filling an R12 system with 134a you'll need less volume to achieve the same operating pressure - even more reason to get the compressor running and care not to overfill. If the pressure switch is a dual high/low switch then maybe your pressure is too high??

[rusty9]

Ok thanks for the info. I just told them to evacuate and recharge the system since I assumed everything was working. I didnt want to pay them for diagnostic work since i can do that myself.

should i be able to turn the compressor by hand relatively easily with the clutch engaged and the belt off?

[Mister_Perkins]

When he Evacuated the AC system, did he Jump the AC Compressor relay to make it run while he was charging the system? If not, this is your problem

Also, Switching from R12 to R134A he should have flushed the AC System out before Putting R134 in. If he didn't, you risk mixing the minerals inside of the AC lines and it will gum up and clog your entire system, not allowing proper circulation.

[Stillrunning]

Originally Posted by rusty9

should i be able to turn the compressor by hand relatively easily with the clutch engaged and the belt off?

Can't accurately describe "easily". Too easy and compressor is worn badly (which low pressure will tell), too hard and seized. You should be able to turn it, that will at least tell if it's seized solid. You'll not be forcing it against any pressure as with little to no rpm there's going to be no real volume to have the expansion valve offer much resistance to flow.

He shouldn't have had to jump the clutch to charge it from initial from- vacuum-fill as the pressure switch low setting is only about 28psi. High side off is around 455psi.