I have a 1998 Dakota with the 4cyl engine. About 2 years ago I had the A/C compressor replaced. Everything was fine for about a year and half when it started having issues. It basically works some time, and not others. I have spent the past few months trying to find the problem myself in order to avoid paying a mechanic. The first thing I noticed was that when its not working there is no voltage going to the compressor, so I am assuming that the compressor and fan clutch are fine. When it is working, it cools well. It was 105* today and it was still nice and cool when it was working so I am assuming that refrigerant is not the problem. I checked all of the relays with my ohm meter and they all checked out fine. (80 ohms I think it was)Also, I tried to jump the low pressure switch when it was not working, and that didn't cause it to turn on. I have played with switch on the dash a ton, So I'm pretty sure that's fine too. I think I read somewhere that on more modern cars that a faulty ambient air temperature sensor could cause A/C issues but this my 98. Far from modern. So what else could it be?

 

I have a 98 Dakota that has had a mountain of A/C problems that Ive fixed so I can help but not today.

I will get back to you later check this out it may help http://www.in30.net/index.html

http://www.73js.com/mywebalbum/index.html

 

AIR CONDITIONING COMPRESSOR—3.9L and
5.2L ENGINES
When the A/C-heater control switch is moved to an
A/C position or the defrost position, and the A/C high
pressure and low pressure switches close, the Powertrain
Control Module (PCM) receives an A/C request
signal on circuit C20. Circuit C20 connects to cavity
C22 of the PCM.
After receiving the A/C request signal, the PCM
supplies ground for the coil side of the A/C compressor
clutch relay on circuit C13. Circuit C13 connects
to cavity C1 of the PCM. Circuit A21 from the ignition
switch supplies power for the coil sides of the
relay. Circuit C26 from fuse B in the Power Distribution
Center (PDC) supplies voltage to the contact side
of the relay.
When the PCM grounds the A/C compressor clutch
relay, the contacts close and connect circuits C26 and
C3. Circuit C3 supplies voltage to the A/C compressor
clutch. Ground for the compressor clutch is provided
on circuit Z1.
HELPFUL INFORMATION
Circuit C90 from the A/C heater control switch connects
to the low pressure switch. Circuit C22 from
the low pressure switch connects to the high pressure
switch. Circuit C20 from the high pressure switch
connects to the PCM.
RADIATOR FAN RELAY AND MOTOR
The Powertrain Control Module (PCM) supplies
ground for the coil side of the radiator fan relay on
circuit C27. Circuit C27 connects to cavity C2 of the
PCM. Circuit A21 from the ignition switch powers
the coil side of the radiator fan relay. Circuit C26
from fuse B in the Power Distribution Center (PDC)
supplies voltage to the contact side of the relay.
When the PCM grounds the radiator fan relay, the
contacts close and connect circuits C26 and C25. Circuit
C25 supplies power to the radiator fan motor.
Circuit Z1 provides ground for the radiator fan
motor.
HELPFUL INFORMATION
Circuit C26 also powers the contact side of the A/C
compressor clutch relay.

 

Good luck

 

Why did you replace the compressor?
Did it have black death if so was the complete system flushed out and orifice tube replaced?

When you replaced the compressor did you?


Add oil?
Replace the dryer receiver?
Was the system put on a vacuum for 30 to 60 minutes?

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Have you checked the high and low side ports psi yet?

High side = ____ psi

Low side = ____ psi

Air temp during the port's psi tests Air temp = ____


That's a start

 

Do you happen to know where the high pressure switch would be?

 

About 6 inches out of the compressor on the high side line the low side sensor is plugged into the receiver dryer canister on the firewall of the cab.

Both of these rarely go bad

 

I will say one common problem I have encountered is bad wiring check for bad wires always close to any sensors and connectors these are pulled and yanked on causing broken internal wires.

Causing intermittent on off type operation

 

Actually the very first thing I thought it was that connector.The first time the A/C shut off on me, I wiggled that connector and the compressor kicked back on. But after testing it once and couldn't get any voltage at the prongs on the connector, I figured that was just a coincidence. Maybe I should start back at square one and replace the connector?

 

My wire to activate the A/C clutch went bad and became intermittent I just cut off the connector and crimped the wires together with a short extension wire added in as cutting the connector off made the wires too short that connector sucked anyway.

I used these simple easy and cheap a new dealer only connector runs around $20.