need help recharging AC

[modelageek]

This is for a 2006 vibe/Matrix 130k miles My AC is a little weak. I put a tester on the low pressure side car was running AC on high Doors open 90 degrees outside the pressure was about 39 but went down to about 34 when the compressor kicked on. On a can of 134a at the store it said when 90 degrees pressure should be 45-50 does this sound correct and what reading do you use. The one when the compressor. Is on or off. Thanks

 

[Earl43P]

I use a thermometer in the center duct, med fan speed.

@~2000 rpm, see what it puts out. Add refrigerant and watch the thermometer, keeping the rpms up. I jumper the low pressure switch when adding refrigerant, to speed the flow. Do not drive with it jumpered.

When the thermometer stops dropping, stop adding refrigerant. Should be able to get <45 degree air out.

Then drive it for a couple miles at 45 or so. The temp should drop another 5 degrees or so from what it was sitting still. If it goes up, you may have added a bit too much.

I do all temp readings doors closed, windows up, NOT in recirculate / Max.

It's a fine line.....

 

[modelageek]

I use a thermometer in the center duct, med fan speed.

@~2000 rpm, see what it puts out. Add refrigerant and watch the thermometer, keeping the rpms up. I jumper the low pressure switch when adding refrigerant, to speed the flow. Do not drive with it jumpered.

When the thermometer stops dropping, stop adding refrigerant. Should be able to get <45 degree air out.

Then drive it for a couple miles at 45 or so. The temp should drop another 5 degrees or so from what it was sitting still. If it goes up, you may have added a bit too much.

I do all temp readings doors closed, windows up, NOT in recirculate / Max.

It's a fine line.....

thanks i went to HD to get a plumbers thermometer but they were out of them. so basically you are saying that if I set the ac the way you said I should get a reading on the thermometer of 45 degrees less than outside air. so yesterday it was 90 degrees and if i tested it it should have been 45. if it was higher I should add some 134A?..........and if i put to much in it will not work properly either.

 

[modelageek]

@~2000 rpm, see what it puts out. Add refrigerant and watch the thermometer, keeping the rpms up. I jumper the low pressure switch when adding refrigerant, to speed the flow. Do not drive with it jumpered.

.

do I use a regular alligator clip jump wire and find the low pressure switch. is the switch usually along the low pressure line?

 

[modelageek]

I use a thermometer in the center duct, med fan speed.

@~2000 rpm, see what it puts out. Add refrigerant and watch the thermometer, keeping the rpms up. I jumper the low pressure switch when adding refrigerant, to speed the flow. Do not drive with it jumpered.

When the thermometer stops dropping, stop adding refrigerant. Should be able to get <45 degree air out.

Then drive it for a couple miles at 45 or so. The temp should drop another 5 degrees or so from what it was sitting still. If it goes up, you may have added a bit too much.

I do all temp readings doors closed, windows up, NOT in recirculate / Max.

It's a fine line.....

Per Earls suggestion i went to advanced auto and bought a ac thermometer ($5) I was going to use a meat thermometer but Earl was not thrilled about that. I started the car held the car at 2k rpm put AC on max blower at 2/3 and the temp was at about 42 the thermometer comes with a small green dot between about 38-42 it held at the top of the green dot. also it was about 90 degrees outside........I think I will leave it alone for now. I gave the wife the thermometer to check. I did not feel like listening to the wife all summer that the AC was not working. thanks to Earl and the rest for your help.