Bruno2 Posted July 7, 2022 Share Posted July 7, 2022 My son's 91 has been having some strange AC issues. The damper door that switches from the heater core to the AC evaporator core had been non functioning with the thermostat switch. So I opened the black box up and manually switched it over. When I did that the door didnt shut completely, but was giving up 70 degree air which is better than nothing when it's 100. As far as I can tell the door is cable operated and not vacuum controlled. So today my son was late for work. He was driving 85 mph down the highway. While he was at that speed the AC magically began blowing ice cold. However, when he slowed back down it was back to the 70 ish degree air. Now I am fairly AC savvy. I have done a lot of AC work on vehicles over the years and have pretty good success if you discount the finicky Chrysler/Fiat stuff. I do have a 12 2500 Laramie I retrofitted to 152A that will blow 39 degrees out of the vents when it's 98 degrees outside. With that being said I am not AC ignorant. I am not the Guru either, but this one has me stumped. I cant imagine what a significant difference engine rpm would make on an AC . Especially with the problem he is experiencing mainly relates to a mechanical cable and not something vacuum operated. Any ideas? Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 8, 2022 Share Posted July 8, 2022 So it went back to its warm ways when he slowed down. Bummer. Does that fancy DVM have a thermocouple prob? Can you put it close to the evaporator and see if it is getting cold? And drive it to see when it gets cold? And what about checking the pressures when you rev it up to whatever R's it was turning at 85? Hopefully someone that can spell A/C will come along to help 'cause I am not at all au fait with these things. Link to comment Share on other sites More sharing options...
grumpin Posted July 8, 2022 Share Posted July 8, 2022 My first thought is your condenser is dirty or clogged up with debris and with added air flow, it gets enough flow to get it to cool better. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 8, 2022 Share Posted July 8, 2022 Maybe driving that fast forced enough wind in the cowl to hold the blend door shut? I am NOT A/C savvy, but I'd want to check how cold the evaporator is with the truck standing still. How dirty is his condenser Brandon? Did you try misting a hose into the grille while someone else sat inside to see if it blew colder? Edit: Dane and I are of a similar mind! Link to comment Share on other sites More sharing options...
mat in tn Posted July 9, 2022 Share Posted July 9, 2022 Maybe driving that fast forced enough wind in the cowl to hold the blend door shut? I am NOT A/C savvy, but I'd want to check how cold the evaporator is with the truck standing still. How dirty is his condenser Brandon? Did you try misting a hose into the grille while someone else sat inside to see if it blew colder? Edit: Dane and I are of a similar mind! let's be sure that there are no other parallel symptoms. does the vehicles operating temperature change with these driving changes also? sometimes the thermostatic fan clutch can be bad and not provide enough cooling for the condenser even though the engine may not be as sensitive. a vehicles system has to operate across a wide range of environmental differences. unlike nearly all other small appliance which will have mostly fixed settings. some will have txv design to adapt to some variations but that's limited also. even still, there is a time curve for optimal output Link to comment Share on other sites More sharing options...
Bruno2 Posted July 10, 2022 Author Share Posted July 10, 2022 let's be sure that there are no other parallel symptoms. does the vehicles operating temperature change with these driving changes also? sometimes the thermostatic fan clutch can be bad and not provide enough cooling for the condenser even though the engine may not be as sensitive. a vehicles system has to operate across a wide range of environmental differences. unlike nearly all other small appliance which will have mostly fixed settings. some will have txv design to adapt to some variations but that's limited also. even still, there is a time curve for optimal output Temp stays constant. We just did the fan clutch a year ago because we were experiencing higher temps at idle with the AC on. I need to insert the thermocouple probe into the drain in the black box to see what kind of temp we're getting. Link to comment Share on other sites More sharing options...
Bruno2 Posted July 18, 2022 Author Share Posted July 18, 2022 I didn't have my thermocoupler for my meter. However. The.line right below the orifice tube is cold. So the coil has to be cold inside the box. The vent.is still blowing like 70° air. The issue still has to be airflow across the coil, Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 18, 2022 Share Posted July 18, 2022 I didn't have my thermocoupler for my meter. However. The.line right below the orifice tube is cold. So the coil has to be cold inside the box. The vent.is still blowing like 70° air. The issue still has to be airflow across the coil, I agree. Something is going on with the door in the box. Have you pulled the blower motor? You might be able to see something there. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 18, 2022 Share Posted July 18, 2022 I agree. Something is going on with the door in the box. Have you pulled the blower motor? You might be able to see something there. A phone endoscope or even a inspection mirror might help. So, you think it's a possibility that driving *85 might force the door closed? Link to comment Share on other sites More sharing options...
Gary Lewis Posted July 18, 2022 Share Posted July 18, 2022 A phone endoscope or even a inspection mirror might help. So, you think it's a possibility that driving *85 might force the door closed? I have an endoscope you can use, Brandon. Link to comment Share on other sites More sharing options...
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