99 Civic Ex Sedan.
I replaced the following: Dryer, compressor, evaporator and the expansion valve.

My friend has an ac evac machine and has filled the system but the air conditioning only works when the car idles. Whenever the engine is revved up the ac quits working and refridgerant blows out of the compressor relief valve. The strange thing is that the high and low side pressure readings are good. 30 on low side. 140 on high side. Any ideas why this isn't working would be great.... TIA

 

get a new relief valve... Ive never heard of one failing, but I guess it can happen.

I assume that youve already checked and made sure the condensor fan is coming on, right?

 

Yes, the condensor fan runs.

This is actually the second compressor installed on the car. The first replacement was used and refrigerant also blew out the relief valve. I thought there was an issue with that compressor so I replaced it with a brand new one.

Now the same issue is reoccuring with the new compressor. Pressure readings are within spec and don't spike, yet the relief valve opens up regardless after giving it more throttle.

 

Is the high-side service port before or after the condensor? You may have a restricted condensor or pinched line between the compressor and the high-side service port.

Understand what im getting at? 140psi is a bit low for hi-side pressre. Im betting you have a slight restriction somewhere between your compressor and the hi-press sevice port.

Also, too much oil in the system could possibly cause this, but isnt very likely.

 

High-side port is located after the compressor and before the condensor. I was thinking that 140 seemed a little low as well for the high side.

I will try replacing the line or maybe inspecting it after removal. Hopefully the condensor isn't causing the restriction.

What's the easiest way to drain the oil from the system? I'm not sure if my "AC friend" may have overfilled it.

 

Definitely sounds like a restriction, most likely the condensor, but could be the discharge line between the compressor and high side service port.

It is unlikely you would have two compressors with the same problem, bad pressure relief valve.

Also confirm there is oil in the system. 94

 

Great advice, thanks. I took off the condensor and compared it to another used one. Surely enough it had a restriction. I confirmed this by using an airgun and blowed compressed air through both condensors. The air gun wanted to back off the inlet hole of the "bad" clogged condensor if I didn't apply enough pressure to hold it down.

After replacing the condensor we recharged it and it worked well.

Until...i drove it roughly for 2 hours and it started another problem.

So now the ac system works great until you drive over 60 mph. Above 60 mph, it will randomly cut out, but never below 60 mph. It will cut in and out 5 times in a 20 minute interval.

 

Evaporator freezing up?

 

Would also be my guess, check A/C thermostat, #21... http://www.hondaautomotiveparts.com/...G+UNIT+%282%29

Also check condensor fan, is it running in the right direction, pulling air through the condensor? 94

 

Condensor fan is running in the proper direction.

The evaporator and expansion valve have been replaced. However, I did not replace the a/c thermostat. Would the ac still work if it was left disconnected?

I'll check that next and let you what I find...

 

A/C will not work if thermostat is not connected, A/C request, [A/C turn on] is a ground from the A/C switch through the A/C thermostat to the condensor fan relay and the A/C pressure switch and then to the ECU/ECM, the A/C compressor is controlled by the ECU/ECM through the A/C clutch relay and A/C thermal switch. 94