My a/c compressor does not cycle off, while the clutch stays engaged the a/c cools fine. Evantually in a few minutes the high pressure gets over 350-400 psi and the pressure relief valve opens, the top of the condenser gets also very hot. Parts replaced to solve this problem unsuccessfuly: compressor, drier (twice), Exp. valve (twice), condenser, pressure valve on drier, heater module, ECU, all related relays anda/c diode. The system was flushed when parts got replaced. Any help appreciated...please...

 

High head pressures are caused by 1 of 3 things...

No air circulation, [condenser fan not turning on or running backwards] condenser fan should turn on at 150 -200 PSI.

A restriction in the lines, plugged orifice tube or damaged expansion valve.

An overcharged AC system.

So confirm you have the correct charge, make sure condenser fan, [and rad fan] are running and in the correct direction.

If you are able to flush the system properly it is unlikely that there is a restriction.

There is one other possibility, "a/c compressor does not cycle off" if A/C compressor does not cycle, the evaporator will freeze causing the blockage.

I will have to check a couple of things at work this morning and see if there are any problems specific to 98 Civics... http://airwolfeautoair.com/ 94

 

By the way I forgot to mention, I replaced the condenser fan too, and is blowing the right direction - rowards the engine. My concern is why the high press switch does not cut voltage to the clutch magnet. I have a diagram from a generic parts store manual that does not help a lot. I understand there is a themostat on the evap housing that I am not seeing on the schematic that may be responsible for the compressor staying on. can anybody tell me the power flow for the high pressure circuit that are supposed to protect the compressor?

 

The Control Head, [Heater Control Panel] A/C request output is a ground, [blue/red] to A/C thermostat, [blue/red].

The A/C thermostat has a 12V+, [black/yellow], fuse 17 - 7.5A, [hot in run], in under dash fuse box, not sure why, probably because A/C thermostat is "solid state".
Output from A/C thermostat is a ground, [blue/white] to Condenser Fan Relay, [coil] and a parallel output, [blue/white] to A/C Pressure Switch input.
Output from A/C Pressure Switch is a ground, [blue/red] to PCM/ECM.

The PCM/ECM has two outputs related to the A/C system...
A low current ground, [black/red] to A/C Compressor Clutch Relay, [coil].
A low current ground, [green] to Radiator Fan Relay, [coil], it is paralleled with the output, [green] from the Engine Coolant Temperature Switch.

Questions...
What is the A/C refrigerant charge, how many ounces of R134A are you putting in?
How are you charging the system, "automatic" machine or A/C gauges, vacuum pump and a charge cylinder?
How long is the evacuation, the minimum. 45min. to 1hr or less?
I assume the A/C, [compressor] can be turned off with the A/C switch on the control head, is that correct?
Will the compressor turn off if you unplug the A/C pressure switch, [no matter what the head pressure is]?
Does condenser fan turn on as soon as you turn on the A/C?
Does rad fan turn on as soon as you turn on the A/C?
Do both/either stay on as long as the A/C switch is on?
How long from the time A/C is turned on does it take for the head pressure to reach 200 PSI?

I know it is a lot of questions, please answer them all, troubleshooting an A/C problem over the Internet is not easy, and in your case, [depending on answers] I may start pulling my hear out. 94