Long story short I put a new motor in my wife's civic ex then recharged the AC using 2 cans of r134a. Works great when you stay around 55mph or lower. When your on the interstate the AC seems to blow cold for a min then hot. So its basically off and on. I had the system vacuumed two days ago and it pulled -22psi so I know there's no leak. After having it vacuumed I re-charged with two 12oz cans (book calls for 22oz) and same deal. Off and on off and on. Has anyone experienced this? If so was there a solution.

Condenser fan is running. Pressure was around 200psi on the high side if I remember correctly looking at the gauges when vacuumed.

 

You overcharged the system with refrigerant. You need to add refrigerant by weight using a scale and not rely on amount stamped on the can.

 

If it was overcharged would the low side pressure be more than 42-45psi I'm getting now? I tried with 1.5 cans and got the same result except it never really got cold.

 

A low side refrigerant pressure alone is not very informative. Other conditions must be included, such as high side pressure, outside temp and humidity, engine rpm, A/C setting, and air temp output from vent.

Below is the proper way to performance test your A/C system. In step 1, you obviously would hook up a manifold gauge set rather than a professional charging station.

 

Here's something else to consider.

You did not pull a deep vacuum, which is about -30 PSI. Therefore, there's likely air and moisture in the system. In addition, did you replace the receiver/dryer just prior to evacuating and recharging the system?

 

I let the pump stay on for a good 15min once it reached -22psi. Guess its possible the gauge was bad. I did not replace the dryer.

 

It's clear from your posts that you should:

1. Recover the refrigerant
2. Replace the receiver/dryer
3. Pull a deep vacuum (about -29 PSI) and leak check
4. Recharge system with the proper refrigerant weight and oil volume
5. Performance test system as per diagrams I posted.

 

that's at sea level:

http://www.anver.com/document/vacuum...20pressure.htm

still looks like he didn't attain an adequate vacuum. but he may never be able to reach 29 or 30"Hg if he's at altitude. use a can of R-134 with UV dye and a UV light to help find any leaks. one of my used hoses leaked at the compressor.

 

Yeah you didn't pull a good vac. Try to find another set of gauges and vac and do another pull to be sure. -22 is still not good enough. I know I get -32 or so when I was living in Louisiana. What I usually do is let it pull a vac for 15 minutes and then close off both valves with the ***** on the gauges and wait to see if pressure rises. If it does than you have a leak.

 

X2 great post

 

Replaced the drier and Had the system vacuumed again to -27psi and left it over night. Still had a vacuum on it next day. Added one can of r134a and showed around 47psi on the low side at idle so I left it alone and took it for a test drive. All was well and didn't cut off in 15min of driving. Hit the Interstate and after about 10min it started blowing hot for a few secs the back cold for 5mi or so then back hot. Seems like the further I went the more frequently it would switch back and forth. When in the car I can't feel the compressor kick off. Any other suggestions?

 

High side pressure? Outside temp?

 

Not sure. I'm having to take it to a friends shop to vacuum and he has the gauges. I have a lowside gauge and when you rev the car over 2k rpm the pressure drops below 20psi

 

Replace the receiver drier for sure. Its a PITA but worth it. Also the correct weight of charge is critical. Otherwise your gas will expand prior to or after the evaporator. But I vote for contamination with your intermittent cooling.

1.Recover the refrigerant
2.Replace the receiver/dryer
3.Pull a deep vacuum (about -29 PSI) and leak check
4.Recharge system with the proper refrigerant weight and oil volume
5.Performance test system as per diagrams I posted.
^rhis