A/C Diagnostic help

[Mogman]

So the last issue I am having with my AC, may not be an issue at all. It pertains to the rear evaporator like in the 1165 and 1151.

It will randomly shut off(stop blowing air) and then start back up again 30 seconds, a minute, some short time later. The front evaporator blows as normal during this time. Also, the rear evaporator doesn’t seem to have a high/low setting like the front. It just blows in what I assume would be high, the whole time.

maybe both of those are normal? I wouldn’t know. Or maybe it’s a safety shutoff for some reason.

if anyone with more knowledge of these trucks could chime in, I’m always very thankful.

That evap is likely pulling too many amps and tripping the breaker

 

[thoner7]

That evap is likely pulling too many amps and tripping the breaker

I think you’re onto something. Because if I cycle the AC off then immediately back on, it blows again.

I’ll have to figure out what’s causing it, and then order all the parts with my new valve to save on shipping! lol

 

[Retiredwarhorses]

I think you’re onto something. Because if I cycle the AC off then immediately back on, it blows again.

I’ll have to figure out what’s causing it, and then order all the parts with my new valve to save on shipping! lol

The rear is an evaporator only, the fan speed is controlled by the hi/low switch same as front, the rear evaporator shuts off when the compressor shuts off, the front evaporator will continue to push air because the blower is still going, this is because the front is also a heater Blower.
You still get front cold air with the compressor off because the air is still forced over the evap coil via the fan, once the proper pressures recover, the compressor will cycle back on and will restore cold air as well as the rear evaporator turning back on….if you are short cycling to often? You are low on R134a refrigeran.
This has nothing to do with over voltage…

 

[thoner7]

The rear is an evaporator only, the fan speed is controlled by the hi/low switch same as front, the rear evaporator shuts off when the compressor shuts off, the front evaporator will continue to push air because the blower is still going, this is because the front is also a heater Blower.
You still get front cold air with the compressor off because the air is still forced over the evap coil via the fan, once the proper pressures recover, the compressor will cycle back on and will restore cold air as well as the rear evaporator turning back on….if you are short cycling to often? You are low on R134a refrigeran.
This has nothing to do with over voltage…

That would be frustrating, seeing that I’ve had it back to that shop twice. If that’s the problem I’ll have to take it somewhere else.


is this the best page the manual?


I guess I don’t understand how they measure the weight of the refrigerant? Is it possible to know how many pounds are in there? Or would the gauges just read correct psi going off this chart, and you’re good…?

 

[Retiredwarhorses]

That would be frustrating, seeing that I’ve had it back to that shop twice. If that’s the problem I’ll have to take it somewhere else.


is this the best page the manual?
View attachment 947068

I guess I don’t understand how they measure the weight of the refrigerant? Is it possible to know how many pounds are in there? Or would the gauges just read correct psi going off this chart, and you’re good…?

View attachment 947069

pressure chart is best, as well as temp gauge inserted into one of the vents while on full, running at 1500rpm…the TM calls for 3lbs 8oz, but that does depends on the pressures banned on air temp.

 

[thoner7]

pressure chart is best, as well as temp gauge inserted into one of the vents while on full, running at 1500rpm…the TM calls for 3lbs 8oz, but that does depends on the pressures banned on air temp.

I did get the 40 degree temp about of both evaporators.
Maybe there’s where I’m confused now. The image above, right side, line item 8 says 5lbs 8oz of refrigerant. So perhaps I’m high, not low?

but as a general automotive question, the guy at the AC shop wouldn’t need to know that amount regardless if he followed the pressure charts?

And my rear evaporator definitely only runs on high .

 

[Retiredwarhorses]

I did get the 40 degree temp about of both evaporators.
Maybe there’s where I’m confused now. The image above, right side, line item 8 says 5lbs 8oz of refrigerant. So perhaps I’m high, not low?

but as a general automotive question, the guy at the AC shop wouldn’t need to know that amount regardless if he followed the pressure charts?

And my rear evaporator definitely only runs on high .

that 5lbs has to be a “typo”, cuz the service label on the trucks say 3lbs 8oz….but yes, follow the pressure chart.