Low pressure switch - cutoff pressure for R134a

[Michael]

I put 2.1 of 134 in mine but then added about half a pound later on. I noticed the low side was a bit weak when adjusting my low pressure switch.

[David T]

I put 2.1 of 134 in mine but then added about half a pound later on. I noticed the low side was a bit weak when adjusting my low pressure switch.

Be careful. 2.1 lbs less 10% is 1.98 lbs. 2.1 lbs plus .5 = 2.6 lbs (Way too much, PERFECT!) R-134 runs a higher head pressures so you must reduce the amount of refrigerant to keep the head pressures from getting too high. Excessive head pressures and you will blow the relief valve and possibly hoses. Don't try to add -134 to get the same cooling capacity as you had with -12. The condenser coil is not sized large enough and the relief valve is set too low.

[Michael]

What should my vent temps be on a 90? day. I'm getting 55-60. Pressures look good although the high side is reading a bit low but still acceptable.

[82DMC12]

What should my vent temps be on a 90? day. I'm getting 55-60. Pressures look good although the high side is reading a bit low but still acceptable.

Hey GOAT!

Last week it was 89F in Kansas City on my way home from work. I actually had a vent temp thermometer and I was recording 38F after about 10 minutes of driving with R134A. I was able to maintain that temp while cruising about 40 MPH with vent speed on 2 or 3 and dial set to MAX AC. If I was slower than 40-ish or at a stop light, the vent temp went up to maybe 42F but then quickly went back down to high 30's once I was moving nicely again. Very comfortable and even better with my recent install of ceramic tint.

This is with a Sanden 7 piston compressor (SD7H15), DPI hose kit, generic parallel flow condenser, stock evaporator, new accumulator and white orifice tube. I still have the low pressure switch cutting out around 21 PSI.

PXL_20240620_223810384.jpg

[Michael]

Wow...definitely have a problem here. My AC has been jacked up ever since they punctured my low side line at a garage when doing a complete cooling hose change.

Long story.

Maybe I'll post a vid tonight of the gauges during compressor operation and compressor cut out

[Michael]

I ordered a ac recovery machine. I'm tired of taking my car to Neanderthals just because I don't have the proper equipment. I'm going to pull it down, put 2.1 in and go from there.

[82DMC12]

I ordered a ac recovery machine. I'm tired of taking my car to Neanderthals just because I don't have the proper equipment. I'm going to pull it down, put 2.1 in and go from there.

Good move, for the cost of one trip to a shop to get my air conditioning vacuumed and recharged, I was able to buy all of the equipment I needed to do it myself. You'll be glad to be able to pull your own vacuum and confirm it is holding for a long time like overnight before recharging. And then if you find something is screwed up you can fix it yourself without having to pay for a repeat trip to the shop.

Sent from my Pixel 6a using Tapatalk

[David T]

Good move, for the cost of one trip to a shop to get my air conditioning vacuumed and recharged, I was able to buy all of the equipment I needed to do it myself. You'll be glad to be able to pull your own vacuum and confirm it is holding for a long time like overnight before recharging. And then if you find something is screwed up you can fix it yourself without having to pay for a repeat trip to the shop.

Sent from my Pixel 6a using Tapatalk

Leak testing by holding a vacuum is no test. It is only 15 psi negative and just sucks contamination into the system. It won't tell you where the leak is or how big it is. The only good way to test for leaks is with Nitrogen at no less than 100 psi and check the system with bubbles. You can buy used A/C equipment and it doesn't cost a fortune. Your problem will be getting the gasses. You can get a certification on line for a few $$$. Just learn how to handle high pressure gasses safely and use proper safety equipment. You will need the following;
A manifold gauge set with hoses
A GOOD vacuum pump and a bottle of vacuum oil (an electronic vacuum gauge is a very nice thing to have)
A recovery system w/ tank and extra filters/dryers
Tools to remove the service valve cores while under pressure
A spray bottle of "bubbles".
A tank of R-134
A tank of Nitrogen w/ regulator
A bottle of oil compatible with the refrigerant you are using
The rest of the tools you need are just wrenches you probably already have.
A Delta T of 20 degrees is all you need to get. You measure that by subtracting the temp of the air coming out of the vents from the temp in the cabin NOT the ambient temperature outside the car. If you see air coming out of the vents in the 30's you are probably overcooling and will freeze the evap coil. The compressor is not cycling enough.

[82DMC12]

I actually leak tested mine with nitrogen, I find not many DIY'ers are willing to do that. I did though. Requires an additional fitting for the yellow hose as well as a nitrogen regulator. The Amazon regulators are shit, I ended up getting a good one at a welding supply store.

Sent from my Pixel 6a using Tapatalk

[Michael]

After much reading, I think I may have a bad/clogged orifice tube but I will have to evacuate and put the correct amount of freon in before diagnosing.

Actually, as cheap as they are, and it's suspect, would it not be a bad idea to just replace it while my system is empty?