1970 442 new ac system complete. Had system charged, its converted to r34 seemed to be working then after about 20 minutes the ac muffler exploded. Decal on my compressor says to install 4 pounds refrigerant. Was properly vacumned down first. Any idea what could cause this. Everything was rebuilt by Classic Air Tampa florida-------??? Thanks------Greg

Im talking about the canister that is attached to the side of the compressor and has the high pressure fitting on it

 

If decal is for R12 then you charged to that volume, you overcharged it with R134a. Roughly 30% less refrigerant, but needs to be charged by temperature/pressure method. The discharge muffler is the part name. Hope nobody got hurt.

 

No injuries, but it was brutal. So by putting the 4 pounds the old decal called for is in incorrect. Sounds Ike it should be closer to 2.5 to 2.75 pounds. Ok. What is the process for the tempature/pressure method. We were using a ac system machine that does it all by itself, but set the refrigerant level for 4 pounds-----thanks-----Greg

 

The pressure will change with the ambient outside air temp. As it goes up, so does the pressure in the system.
You need a gauge to show the pressure as you charge the system or you will get catastrophic failure (as you have seen).

 

I agree that you likely overcharged the system, but I don't really think that is why the muffler exploded.

I say this because back in my young and ignorant days, I was charging the AC on my 70 Cutlass and I was under the misguided impression that the system would stop accepting freon when it got the correct amount. I kept adding cans of R12 (about six of them, if I remember correctly) until the compressor stopped turning and the belt started squealing. That thing was WAY overcharged and nothing blew up. This makes me think you had a defective muffler, or that the aftermarket one can't handle the pressure that a factory one can.

 

Its my understanding that when the ac is turned on the compressor starts, when the ac is turned off the compressor continues to be turning until the car is shut off. Is that correct ?? Seems like with the compressor continuing to run the pressure would get way too high ?? Thanks----Greg

 

the pully will turn on front of the comp any time the motor runs ,the elect. clutch will drop in and out on the comp and will only run when it calls by the controls unless the clutch has frozen in run or a short in the wires holding in . you should hear and see the back side of the clutch drop in and out when you move the controles on and off hope this helps

 

I thought my 1970 has what they call the ac hold in switch on the passenger side fender, which mine does have and this keeps the compressor locked in until the car is shut off Confused ?? Thanks---Greg

 

Greg
You are correct

 

Yes, 1970 was the last year for that operation. Starting in 1971 the compressor disengaged when the dash switch was turned off. I defeated that "feature" on my 70 Supreme back in the 80s as I thought it was silly.

 

The difference being the refrigerant and the temperature.

 

Yes, I suppose. The temperature in Southwest Louisiana during the summer would be the same as northern Florida - assuming that's where this happened. The pressure with a severely overcharged R12 system was likely higher than a slightly overcharged R134A system.

 

So if the compressor stays on all the time with the clutch locked in once the A/C is turned on till the car is shut off what stops the system from getting too much pressure since the compressor stays on all the time once activated ????? Thanks ----Greg

 

Anybody hear of a recycle switch for this system and if there is one where is it located ??

 

The pressure will just be at the typical operating level, the same as if you had the interior switch in the AC position. Turning the interior AC switch to the off position stops air from blowing out of the vents but the under-hood parts keep operating as usual.

 

Wow, I just noticed this thread, sounds similar to my problem. Check out the thread I just added. To me a/c is like voodoo I don't really understand it.....

 

Not likely. When I was installing A/C in Phoenix the r-134a systems were fairly new and we were learning how to charge them so they would work correctly. One guy was installing a system in a van and forgot to pull the radiator hose out of the fan and started the system up. Charged the system with gauges hooked up and the pressure side spiked at over 600 psi! Once the radiator fan was restored it worked properly with normal pressures. No cooling across the condenser can cause major problems with the 134 systems. I also had a receiver/dryer explode on me as I was looking at it and it was brand spankin' new. No idea what caused it, I put another new one on and it worked perfect. Sometimes they are just bad outa the box.