Howdy

Truck is a '96 2500 4x4, 5-spd, 135k miles.

3-4 years ago I replaced the evaporator and accumulator. All's been well since then... until the other day when:

1. A/c started blowing warm air over period of 1-2 days.

2. Put jumper on pressure switch on top of accumulator.

3. Put gauge on fill port – pressure low at about 15 lbs.

4. Added enough R-134a to bring pressure up to 25 lbs.

5. Compressor ran fine and a/c blew ice cold air.

6. Reconnected pressure switch and turned a/c on again. Compressor did not cycle on.

7. a/c started blowing warm air.

8. Shut off truck and waited 20-30 minutes.

9. Repeated entire sequence above with same result. Gauge pressure was still 25 at start of recheck.

FWIW, we live in a year 'round hot & humid climate so a/c is almost never off.

Any thoughts or opinions about what's going on here will certainly be appreciated. TIA

 

sounds like the pressure is fine but the command to the AC clutch may not be getting there. I would look at the pressure switch since you have already deturmined it has an effect.

 

Could you have pushed a pin back in the connector?

 

Based on your described steps, I'll look at the pressure switch as the cause. Since the system is functional when you jumper, you know the system is good. You're just not getting a triggering signal from the switch.

Check the pins in the connector to make sure they are making contact, then test the switch for continuity.

 

The pins look OK. Does the system have to be evacuated of refrigerant before removing/replacing the pressure switch?


Thanks for the help, Gents.

 

Based on my '01 FSM, the low pressure switch is screwed into a fitting containing a Schrader valve so that the switch can be removed without discharging the system.

 

Thanks alot, Aggie. I have the FSM for my '96 but it doesn't mention the Schrader fitting.

 

This is the description from my FSM.

A/C LOW PRESSURE SWITCH
DESCRIPTION
The a/c low pressure switch is located on the top of the accumulator. The switch is screwed onto an accumulator fitting that contains a Schrader-type valve, which allows the switch to be serviced without discharging the refrigerant system. The accumulator fitting is equipped with an O-ring to seal the switch connection.