Q: ECM won't actuate AC relay

asked by on August 18, 2016

A/C recently ceased working. When it is cool out it works fine, when the temp is above 75 degrees or vehicle is driven for more than 15 min the A/C cuts out. Troubleshot the compressor and determined it was going bad and causing excessive drag on the engine as well as making a chirping sound. Replaced the Compressor, Condenser and expansion valve and all seals involved; ensured to add appropriate oil to the condenser and performed oil balancing on compressor prior to install and flushed the lines and evaporator; drew 30lbs vacuum, checked for leaks and charged the system. Problem still persists. If I ground the clutch relay control thereby bypassing the ECM the A/C clutch engages and system works. Static pressure is roughly 110lbs, when clutch is engaged low is around 60 high is around 240. Pressures are good and the system can cool if the ECM would let it. Fairly certain the pressure switch is serviceable as the 5v reference is present and the signal voltage is within tolerances. help

My car has 180000 miles.
My car has an automatic transmission.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

How does the luggage compartment light work?
Unlike your car’s dome light and map lights, the luggage compartment light does not come on when you open the door. However, you can turn it on and off as you need to provide illumination when loading or unloading the...
Need to fix Check Engine light.
The powertrain control module (PCM) turns on the check engine light when it detects a problem in one of the onboard systems. At the same time it also stores a diagnostic trouble code (DTC). These codes help technicians diagnose problems...
Clutch pedal will not retract
The most common cause of a clutch pedal that will not retract is the clutch itself, or the slave cylinder. With the clutch not disengaging, this vehicle is not safe to be driven until the repairs have been completed. A...
my serpintine belt snaped, i noticed the power steering pulley was bent i re placed it but am not sure if the pulley should spin
If there is no drive belt on the pulley that is on the power steering pump, you should be able to turn the power steering pump pulley freely and easily by hand. If the pulley (shaft) does not turn, that...
Bad crankshaft sensors - would that cause the problem of poor acceleration? 1996 Chevy K1500
Hello - yes, a failed crankshaft or camshaft position sensor (https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-crankshaft-position-sensor) can cause a "loss of power" situation. The ignition system has a limited fallback ignition timing scheme to allow the vehicle to run, albeit with little power, to get...
Car shakes and makes thumping sounds while moving
The engine and transmission mounts should be checked on account of your mention of shaking on acceleration. Thumping sounds are often related to defective tires. If your tires are old and worn irregularly, that would be a suspect. If you...
Vehicle squeaks from back left when accelerating or when hitting a hard enough bump. Dodge charger 2016 50k miles
Hi Gridpa1. Thanks for submitting your question tonight. There are several things that could be causing this type of noise. Most common is that a rear stabilizer bar bushing is starting to wear, but with only 50,000 miles on a...
Purchased a cpo Camry 2016 se special edition from a Toyota dealer. My car while driving just locked its brakes and I crashed
There are a number of things that may have caused this, but unfortunately this will require an inspection by a professional to determine what may have caused this. I would suggest taking the vehicle back to the dealer to have...
Hi, we just replaced head gaskets on my 2003 f150 4.6 triton, put it all back together and its seized up! Won't turn over or anyth
You should try to turn the crankshaft with a breaker bar and socket on the center crankshaft bolt. If it cannot be turned then you have the timing chain on wrong and may have bent the valves. Open up and...

Related articles

How Long Does an AC Control Module Last?
Over Over the past decade, vehicles have become far more electronic than they are mechanical, with numerous computers on board that control various functions. Your AC control module is one such computer, and it works to manage the air conditioning...
P0531 OBD-II Trouble Code: A/C Refrigerant Pressure Sensor Circuit Performance
P0531 code means that there is too much or too little A/C refrigerant, high system pressure, faulty wiring, connectors, or cooling fans.
How to Replace an Evaporator Temperature Sensor (Switch)
The air conditioning system has an evaporator temperature sensor that fails when there is no cold air or the air conditioning is inconsistent.