AC compressor does not engage

What are the operating pressures in the system? To see if it even has any r134A in it toss a gauge set on it. if it has any in it you should see a pressure close to the air temperature in Fahrenheit. If you are sure it has a good charge and the compressor is not coming on, you could jump twelve volts to the positive side and see if it engages and cools.
Here are the relays, diodes. The clutch fuse is fuse 20, the main HVAC control fuse is fuse 36 both in the dash fuse panel.

I checked fuses number 36 and 20, they are not defective. I do not have voltage at the red/white wire on connector next to A/C clutch. the other two wires are ground coming from ECM to compressor. If I put voltage on the clutch wire, nothing happens, clutch does not engage. the pressures on ac gauges are 96 low side and 195 on high side. What do you think?

96 low and 195 high without the compressor running are not correct. With no compressor operation the system should stabilize to a pressure almost equal to the outside ambient temperature in degrees Fahrenheit. So if you have a 95 degree day and the compressor is not working you should see a resting pressure of 95-98 psi on both high and low sides.

If you put twelve volts to the red/white wire and got no clutch engagement then the clutch is bad. It has a replaceable coil that is easy to remove and replace.
The other two wires are the thermal switch that opens if the compressor gets hot.

I suspect you have two issues, the odd pressures suggest a bad expansion valve that is stuck/plugged and the bad clutch.
Once the clutch coil is replaced and the compressor is working you can watch the pressures to see if the expansion valve is bad.

A/C gauge readings with engine off, 110 lbs on low side and 108 lbs on high side. I replace the A/C clutch relay and A/C condenser relay under hood; the A/C compressor came on and turned off after a few seconds. I will check if there is voltage at A/C clutch.

Good call, here is a guide that will help

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here is another guide that can help.

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

Please let us know what happens.

Cheers, Ken

OK if the compressor came on then it may not be a bad clutch. It does show that the PCM is able to activate the clutch relay so the control side is likely OK.
110 low/108 high would be about 105 degrees F for air temperature. And it should mean enough 134A for the switches to work.
At this point I would probably recover the 134a in the system. Change the expansion valve. Recharge it with the amount on the compressor tag and then check for operation.

Sorry I have not responded sooner; I had the compressor working and cooling , and the cooling fan was not working, so I replaced the relay and it worked. Suddenly, the starter went out. I ordered a new one and should it on the engine soon so I can start the engine again. I will keep you informed,
thanks,

Sounds about like my vehicles... Replace one part and the rest get jealous... No rush, we'll be here.

Okay, the engine cranks and starts. When I turn a/c on, the ac is cooling, low pressure at 30-35 lbs and high pressure at about 200 - 250 lbs, but, as it cools, the high side goes higher and the a/c condenser fan in front of radiator does not come on. I replace the a/c condenser relay, the one that is between the fan control relay and the radiator fan relay and the condenser cooling fan motor does not come on. I check for voltage on the blue wire, there is none. If I put 12 volts on the blue wire, condenser fan comes on and the compressor low side and high pressures read 35 lbs and 250 respectively. What can I check next?

The problem seems to be that the condenser fan in front of radiator is not coming on.

Pressures sound about right for 70 degrees or so. The fan not coming on is an issue though. When it hit's 225 or so the AC pressure switch should tell the PCM to kick the fans to high speed. As neither is turning on I would suspect the pressure sensor. It should have ground to the black wire, reference voltage to the red wire and the signal comes out the green wire. It's possible a bad connection or bad sensor.

Do you suspect the ac pressure switch or ac pressure sensor? Where is (are) they located so I can check, I appreciate your help,

Ursulo

Yep, it is down in front by the compressor, here is a diagram that shows its location. (below)

the green wire sends signal to condenser fan? is it voltage 12 volts?

I believe so, here is a full wiring diagram of the system to help you with the testing. (below)

How do I test the red, green and black wires on the a/c pressure sensor?

Red should have 5 volts reference voltage on it. The black wire is ground. So if you put a voltmeter on them with the key on and AC switched on you should see 5 volts.

To check the signal output measure the voltage on the green wire. With the AC on and high pressure below 212 psi. you should see .7 to 1.94 volts. With high pressure over 213 psi you should see a voltage from 1.95 volts up to 4.5 volts.

If the above check out then you will need to check the control signals out of the PCM to the fan relay.

The red wire has 5.0 volts, and the green wire has 2.20 volts with high side pressure at under 212 lbs and increasing up to 3 volts with pressure up to 350lbs and the engine seems to change rpms and the condenser fan does not come on. Is is the sensor, incorrect readings? It will read almost 4 volts and high side is at 400 lbs.

The switch will cut the AC off at 4.5 volts which is around the 450 psi mark. So I would say the sensor is OK. That signal feeds into the pcm and it determines the fans speeds and running condition. The PCM then turns on one or both fans as needed.

You wrote that before the starter died you replaced the relay and the fan worked for a bit correct? Then it stopped working. If that is correct I would really check that relay socket. A loose pin might account for the problems. I would also check the signal right at the PCM for both the sensor and the relay.

Okay, what are the voltage and / or readings on the a/c condenser relay? With key on and off? What is the pin no. for the sensor and relay at the PCM?
thanks,

This is the fan control side of the system. I marked the pins for the sensor on the PCM. The reading you get on the green wire at the sensor should be the same at
pin 16 in connector A. You already verified the power and ground. on the other pins.

The way the fans are supposed to operate is somewhat simple.
When you turn on the AC the control head sends a signal to the PCM asking for AC. The PCM activates the clutch relay. This section seems to work as the clutch engages. Now the same signal comes in on circuit A at the top left of this diagram.

It's on this section that controls the fans that there is a problem.
All of the relays are 12 volt with ground side control by the PCM and they all carry 12 volts to the fans or other relays.

I believe you said that the engine cooling fan still comes on but that the AC fan(s) don't correct?
In that case the blower motor relay is OK. The radiator fan diode and relay are working as are ECT 1 and 2.

Check fuses 15 and 6, those power the AC fan and relay.
Check that the fan control relay is the correct one, it has a blocking diode inside that could have failed. It will be a 5 pin relay. The other 4 are 4 pin.

HI, I checked fuses 6 and 15 on fusebox below dash. Fuse 6 has voltage and fuse 15 does not have voltage with key off engine off or key on engine running with a/c on. Where does it get the voltage from?

Fuse 15 gets power through fuse 11 and a control relay. Fuse 11 and that relay have to be working though. Without them the car wouldn't start and run as they also activate the Air Fuel meter and part of the EVAP system.

But it's very possible the fuse contact(s) for fuse 15 failed. Pull the fuse and test right at the terminals in the box. Key on engine running one should have 12 volts. That is the side from the relay. If you have voltage there see if the contact is loose weak. If you get nothing you can try the test I have below.

Take a piece of wire with a 7.5 amp fuse inline and jump 12 volts from the battery to one terminal at a time of fuse 15 with the engine on and the AC on. If the fan(s) start working you have found the problem.

There are a couple ways to repair this if it turns out to be the problem. One would be to add on a relay. The other is to replace the fuse box.
Lets see what the testing shows first.