Altima 2000 air conditioning problem with ECM

Hi. I own a Altima GXE 2000 from 2004.

I had intermittent air conditioning problem 5 months ago. Sometimes it blew cold air and other times only warm air. Then, after I went to the mechanic who couldn't find the problem, it completely gone dead.

So I took it to the dealer shop. They said it was ECM computer, so I replaced to the used one in the other shop. Then it worked intermittently again. But soon after, it's gone dead again. Having searched the internet, in many case the problem is on temperature control amplifier. So I asked to another mechanic to see if it works fine after changing it to new one but it didn't work for mine.

Again, I went to the dealer explaining my problem this week. They think it is ECM again, stating that the ground is not coming up from ECM for air conditioning.

My feeling is that ECM truly does not ground up for air conditioner. But the initial reason is wires or temperature control sensor. Either of them gave overhead to the ECM so that the ground part for air conditioner became malfunctioning. Probably, it intermittently worked because of the sensor and then the mechanic gave too much overhead by turning frequently on/off.

I am on my way of making a decision whether I need to install new ECM($1150 including labor), or ask them to look into the other possibilities such as disconnected wires. They said it will take 2.5 hours to completely look into the problem.

There are enough freon and no leaks. Compressor is fine since it works when manually triggered. The problem is it does not kick in with the switch.

Someone suggested me to just connect battery to the compressor and then to the switch ignoring ECM and temperature controlling issue.

If any one has any opinion or the same experience or hopefully answer, I would greatly appreciate for sharing with me.

Thanks in advance.