98 K2500 ECSB 7.4L 5-SPEED

[Husker6.5]

Either a break in the switched terminal from A/C ON-OFF switch to the + side of the relay's coil, or a bad A/C ON-OFF switch easy enough to trouble shoot. Run a LONG jumper from the N/O side of the A/C ON-OFF switch to the + of the relay coil. If you turn ON the A/C and the coil engages the relay and your A/C system comes on - you have a break/bad connection somewhere in the wiring harness between the Dash A/C switch and the relay to the A/C system. If the coil doesn't engage the relay and turn on the A/C - then the dash A/C ON-OFF switch is bad.

OR:

You can pull the connector off the dash switch and then put a VOM on the hot side and to the load side of the switch and see if you get 0 Ohms in ON position, if so, switch good and use the LONG jumper method to see if harness/connector is the issue. If you get Infinite resistance, then you know the dash switch is bad and then if you put in a new switch, check for harness/connector issues with the jumper!

 

[MrMarty51]

Be sure that the relay ground terminal is getting a good grounding.

 

[Husker6.5]

Be sure that the relay ground terminal is getting a good grounding.

I though he already said he checked that, @MrMarty51. If not, yes, definitely check to make sure the fuse/relay block ground for the relay has good continuity to ground.

 

[smokymtn65]

I assume the "ground" is the trigger for the relay. So wherever is goes is staying open. Is that right?

 

[MrMarty51]

I assume the "ground" is the trigger for the relay. So wherever is goes is staying open. Is that right?

Trigger is signal wire from the switch. Other side of that trigger wire through the relay must have a good ground or the trigger circuit wont be completed.

 

[MrMarty51]

 

[Husker6.5]

View attachment 66848

Terminals #86&85 are the electromagnetic coil terminals. As you see, a good ground for #85 is critical to energize the pull-in coil to close the spring-loaded switch across terminals #30&87 to complete the circuit and power the A/C system.

 

[smokymtn65]

I understand that part but what i needed i guess was were"30" goes it's the issue.

However i have partially solved this, there is a pigtail behind compressor the plug.is simular to the one on the low side at accumulator. So are there two low pressure switches or two high pressure switches on these? I jumped it and ac cycles. Since po removed everything not sure what i am missing lol.

 

[Husker6.5]

Start with a good wiring diagram and start tracing.

 

[Husker6.5]

I have a "98 GMT-400 GM Factory set of shop manuals. If you want, I'll pull them out and post photos of the wiring diagram for your engine and the A/C system.

 

[Husker6.5]

Iirc, #30 grounds through the fuse/relay box frame to the panel it's mounted to. Just stick one probe of the VOM in it's socket in the box and the other end to a good ground and see if you have continuity. Posting photos of everything you're dealing with always helps.

 

[Husker6.5]

As I was. #30 gets its power from the Key On (+)Buss Bar in the fuse/relay box.

#85 grounds through the fuse/relay box's frame/ground bar to whatever metal panel it's attached to. So, if you get other than continuity (bright continuity light) or VOM of more than 2 Ohms, check if there's corrosion around those mounting points/bolt threads that attach the box. . .

 

[smokymtn65]

Mystery solved. Since the whole ac system was mia. I never thought about the compressor having a switch in the back. It has a switch in the high pressure line . So jumping the connector ac works. Does anyone know , is it a high pressure or low pressure that goes in the rear of the sanden style compressor?

 

[MrMarty51]

For some reason I’m thinking that is a low pressure switch. It aint gospel though until someone else confirms it.

 

[smokymtn65]

One piece at a time. Do some fitting , then do some coating and install..

 

[Husker6.5]

One piece at a time. Do some fitting , then do some coating and install.. View attachment 66930

Well, it looks like you got the start on the legs and body. Next thing you know, you'll have made a Tin Man. Then get yourself a pair of Ruby Slippers, a picnic basket with a little mutt in it and a blue gingham dress, and you should be good to go, Dorothy!

 

[smokymtn65]

Kansas here we come! Lol

 

[Husker6.5]

Kansas here we come! Lol

You're better off staying in Oz!

 

[n8in8or]

I haven’t been getting notifications on this thread for some reason. Not sure if you figured it out yet or not, but here’s some info from my 98 service manual. Let me know if there’s anything else you’d like pics of.

 

[Husker6.5]

I have a set of those manuals. Worth every pound of weight, too!