I've got a 2010 Civic EX coupe with a Viper 5902 alarm system (including remote start). This past week, I had to have the Viper dealer disconnect the Viper 5902 "brain" because it was starting to drain my car battery overnight.

He disconnected the Viper "brain," and the battery drain stopped. But as soon as it was disconnected, the A/C stopped working right.
Now the A/C only cools intermittently when the car is being driven, except at the highest engine speed. Tests showed that pressure on the low side keeps dropping from 30 pounds to 10 pounds, cause unknown.
The A/C is fully charged with coolant, and we can't find any leaks.

So he reconnected the Viper "brain"-- and presto! The A/C started working fine again! But of course, now I've got the battery drain problem back.

My mechanic and the Viper dealer both swear that there is no way that this can happen, and that the A/C failing and then working is just some horrible coincidence. I'm just not buying that.

I'm desperate. Does anybody have any idea what could be happening here? I've talked to another mechanic, and he's stumped too.

 

The issue may be related to the defroster/climate control circuit if the Viper remote start wiring was connected to it. Sometimes wiring needs to be reconnected or repaired after removing or unplugging alarms/remote starts depending on how the wiring was done. When the defroster is turned on, generally the A/C would be running.

 

The A/C relay on those cars are known to stick and cause a battery drain. If they ran the viper through the same wires then you're probably overloading the relay.

 

This guy is right. The Omron which is the cheapo relay Honda used is prone to failing. It will work off and on. You need the Mitsuba.

2006 HONDA CIVIC 1.8L L4 A/C Compressor Relay | RockAuto

The Omron is always going to be the cheap prices one at any retailer and the Mitsuba will be the more expensive one.

 

Yes! I took the car to an electrical repair specialist, and that is exactly what he said.

He even said that he stocks plenty of replacement A/C relays precisely because it's such a common problem.

We found the "smoking gun."

Thanks for your help. Appreciate it!