My dash A/C works great although it will lose some R-134A over several months time. I added a can and a half about four months ago (hose with vale and gauge from auto store). I noted at the time that the low pressure side was holding about 37 psi. Anyhow, just recently it started blowing a little less cold than normal. I added one can and got it up to around 30 psi. Then I started the second and checked the pressure as I did so. (shut valve, let settle, check) It was at this time that the pressure reading started bouncing from 25 or so to 35 or so. Anyhow, I didn't add any more and the A/C is operating fine so what's the deal? Thanks.jor

bad gauge on the can? i think on the can i just put in it said to charge to 50psi?

I agree it is hard to know actual PSI from these cheap kits. Be careful and do not over fill. If it cools then I tend to stop.I keep on in an AC vent that I can see while driving.

Without knowing what kind of system we're talking about, and where the gauge is being connected, hard to say what a reading should be. It won't cool if overfull with refrigerant, Just ahead of the expansion device, the low side pressure ought to be in low-to-mid 20's. But I wouldn't put mich trust in a cheap gauge or the advice of a sales person at most auto supply outlets.If it's a good gauge, properly connected, a fluctuating low side reading can be moisture in the system, freezing at the expansion device, then melting or breaking up to allow flow to continue.

My experience is that it will jump around like that when it's low on Freon due to the compressor cycling on and off quickly. Did you notice if that was the case with the compressor?

After so many times of leaking and adding new refrigerant, air is getting into the system...time to completely discharge, and vacuum all the air out, find and repair the leak, and recharge with the proper amount of refrigerant...air in the system can cause a false pressure reading, too much refrigerant will cause a lack of cooling because the system can't convert the refrigerant from liquid to vapor efficiently.

Charging Dash A/C | Good Sam Community

12 Replies

dougrainer
Nomad
Sep 26, 2013
Need to make sure of one thing on this post.
You CANNOT tell the full charge of a AC system from gauge readings. You can tell if there are problems from what the gauges read, but you can NEVER watch a Gauge and know when it is fully charged. A HI side gauge WILL tell you when you are OVER charged. Doug
time2roll
Nomad
Sep 26, 2013
Next time the cooling gets poor take it to a shop to service it properly.
Gives you time to talk around and find a good service facility.
joraz
Explorer
Sep 26, 2013
Jor how many pounds of gas to fill from empty?

Not really sure. My documentation doesn't cover that. When it blows less cool it shows about 10psi. I'll have to do or have done some real diagnostics and get it fixed properly one of these days. We live in Tucson so our local trips often require A/C.
jor
dougrainer
Nomad
Sep 25, 2013
riggsp wrote:
After so many times of leaking and adding new refrigerant, air is getting into the system...time to completely discharge, and vacuum all the air out, find and repair the leak, and recharge with the proper amount of refrigerant...air in the system can cause a false pressure reading, too much refrigerant will cause a lack of cooling because the system can't convert the refrigerant from liquid to vapor efficiently.

IF the fill line is purged correctly, NO AIR can get in a system. But, I guess using the shelf systems at Auto part stores(I have professional Gauges/tools) and have never used the shelf type systems, so maybe you cannot purge the fill system on those systems. Doug
Gale_Hawkins
Explorer
Sep 25, 2013
Jor how many pounds of gas to fill from empty?
joraz
Explorer
Sep 24, 2013
Yea, I know I'm going to have to find the leak one of these days. The system is on a 40' Foretravel motorhome. The compressor is in the back and the condensor and fans up front. I have been using the auto store cheapo gauge and setting the pressure according to the instructions re ambient temp. Come to think of it, the second can refused to completely close up when I extracted the needle valve. Anyhow, thanks for the advice. It's cooling well now so I'll just leave it alone for now.
jor
Gale_Hawkins
Explorer
Sep 24, 2013
2x on starting over. After doing that on a dirty R-134a conversion going with new green O rings, vac and dryer we have had flawless cooling so far.
riggsp
Explorer
Sep 24, 2013
After so many times of leaking and adding new refrigerant, air is getting into the system...time to completely discharge, and vacuum all the air out, find and repair the leak, and recharge with the proper amount of refrigerant...air in the system can cause a false pressure reading, too much refrigerant will cause a lack of cooling because the system can't convert the refrigerant from liquid to vapor efficiently.
LakeLifeTL
Explorer
Sep 24, 2013
My experience is that it will jump around like that when it's low on Freon due to the compressor cycling on and off quickly. Did you notice if that was the case with the compressor?
j-d
Explorer II
Sep 24, 2013
Without knowing what kind of system we're talking about, and where the gauge is being connected, hard to say what a reading should be.

It won't cool if overfull with refrigerant, Just ahead of the expansion device, the low side pressure ought to be in low-to-mid 20's. But I wouldn't put mich trust in a cheap gauge or the advice of a sales person at most auto supply outlets.

If it's a good gauge, properly connected, a fluctuating low side reading can be moisture in the system, freezing at the expansion device, then melting or breaking up to allow flow to continue.