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Did the can get cold, did the metal lines going through the firewall get cold? Despite directions on some cans that say hold it upright I've found that upside down, move it around, shake it, helps. Center outlet air temp on high/recirc on a properly working system should be 45-50 degrees. It does better with the car moving and air is flowing through the condenser. If its nowhere close to 50 and the compressor is clutching or clutched and the system won't take more refrigerant then it could be a restriction in the system.
 

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You should expect around 20-30 degree Delta T ( the difference between outside ambient temp and air out of the vents. That is with a fan blowing on the front end of the car or while driving.

The can will charge liquid if you hold it upside down and gas in the upright position .. for example if you were charging and the pressure spikes to 45+ on the low side with a liquid charge you can turn the can sideways to go between gas and liquid .. that is until your low side pressure equals the pressure left in the can = 30 psi not moving is not necessarily an empty can but it won't suck or push any more refrigerant into the system.

My Auto HVAC instructor would tell us "there is no such thing as cold air .. just air with less heat in it."
 

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Just to verify: when you used the can, you saw pressure increases each time you checked the pressure after each cycle of adding refrigerant?
Sorry, I wasn't focused on the pressure, just noticed that it went up and down as the compressor cycled on and off (or off and on). According to my notes I only added one can. I imagine if I added one can and it helped a little I would add another can. But: I wonder about the compressor running continuously. I'm no expert but I expect it would either not be running or cycling rather than running continuously.
 

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Discussion Starter · #28 ·
But: I wonder about the compressor running continuously. I'm no expert but I expect it would either not be running or cycling rather than running continuously.
I mean I have previously witnessed it cycling on and off, especially in more moderate ambient temperatures.

But during this specific recharge process (which took maybe a few minutes altogether) the compressor was on and stayed on.

The can I bought was a 12 oz. can (i.e., the smallest they have and the only one without any sealer additives), and I didn't even use the whole contents. I was just concerned about seeing zero change in pressure.
 
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The right way to do it is to have the system fully evacuated and the have the correct amount of weighed refrigerant put back in, eg take it to a shop.

The not-right way that's still better than those recharge systems is to buy a set of AC gauges and use the 12oz refrigerant only cans. Using those you can at least purge the lines so no air gets into the system but its still not going to be a truly accurate charge, you can get into the ballpark enough to blow cold air using the pressure/temperature charts though but you might end up overfilling the system.

Like Dan said you probably have a leak in the system somewhere, topping off the charge without finding it isn't a permanent fix
Having just been through this, pay a shop the $200 to fix it properly.
 
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