HVAC Issues

doo dah · Mar 17, 2021

I have searched but none of the posts I found had the same issues, or at least description of issues, that I have. Last summer my truck would blow cold air and then hot, it wasn't cyclical rather once it went hot it would not blow cold sometimes for days. Did some research and bought the new evap temp sensor and plugged it in without removing the old one. Blew frigid cold for about 15 minutes then no air coming from the vents and what felt like cold air coming from the floor vents. Turn a/c off and leave vents on and eventually air started coming from the vents, cold at first eventually becoming warm. I figured the sensor was freezing the coil and the initial cool air was just outside air blowing over the coils so I got a recharge kit and system was a little low on pressure so added a can. Tried running a/c again and same thing happened so I unplugged the new sensor and plugged the old one back in and we had cold air for about a 3 hour drive. On the return trip home, no a/c just outside air through the vents for a few hours until we were 20 minutes from home and then started getting cold air. I'm at a loss and ready to go to a shop since this doesn't sound like a blend door or evap sensor issue, any suggestions? Thanks!

6.0 Tech · Mar 18, 2021

Sounds like the evap temp sensor is bad. When you plugged the new one in, without removing the old one, was it installed in the evaporator? If it was, it was not in the right spot, and could possibly cause the evaporator to freeze. If it was not installed in the evaporator, then it definitely caused the evaporator to freeze. When the hvac module sees the evap is about to freeze, it shuts the compressor off until the temp rises enough, then kicks it back on. If it thinks the evap is say 60 degrees like it is in the truck, it will never see a reason to shut the compressor off, as long as pressures are good, and will freeze the evap. Shutting the ac off for a bit allows the evaporator to thaw out, and I’ll bet there was a **** ton of water pissing out the evap drain once it started to thaw out, probably got your carpet a little wet too. Any who, there may also be a reprogram for the hvac mod to correct some issues as well. Can’t remember what they were or build dates, but I do remember a run of hvac reprogram o. All sorts of stuff

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doo dah · Mar 18, 2021

6.0 Tech said:
Sounds like the evap temp sensor is bad. When you plugged the new one in, without removing the old one, was it installed in the evaporator? If it was, it was not in the right spot, and could possibly cause the evaporator to freeze. If it was not installed in the evaporator, then it definitely caused the evaporator to freeze. When the hvac module sees the evap is about to freeze, it shuts the compressor off until the temp rises enough, then kicks it back on. If it thinks the evap is say 60 degrees like it is in the truck, it will never see a reason to shut the compressor off, as long as pressures are good, and will freeze the evap. Shutting the ac off for a bit allows the evaporator to thaw out, and I’ll bet there was a **** ton of water pissing out the evap drain once it started to thaw out, probably got your carpet a little wet too. Any who, there may also be a reprogram for the hvac mod to correct some issues as well. Can’t remember what they were or build dates, but I do remember a run of hvac reprogram o. All sorts of stuff

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Makes sense because I have dual zone auto it must be freezing up quickly. Can I cut a hole and install the new sensor in a location close to the current sensor? I saw one picture from one post in all of my searches but no description of how they did it. Really don't want to spend a grand to replace it but don't want to ruin the whole box by cutting a hole only to have it not work.

6.0 Tech · Mar 18, 2021

Honestly, the dashes in these things come out fairly easy. Biggest issue would be recovering the ac to pull the evap/heater case to access it and do it right. I am by no means an interior mechanic, and hate working inside vehicles, and can swap them fairly quickly. But bottom line is, I would not cut a hole in the case, as then you’ll basically have an air leak, and could have less ac performance, and possibly less airflow from the vents, as the air would have another hole to go out. If you have the tools, some sort of mechanical ability, and means to recover the ac, I’d do it yourself. Probably take a day to possibly a weekend for the average joe blows first time.

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doo dah · Mar 19, 2021

6.0 Tech said:
Honestly, the dashes in these things come out fairly easy. Biggest issue would be recovering the ac to pull the evap/heater case to access it and do it right. I am by no means an interior mechanic, and hate working inside vehicles, and can swap them fairly quickly. But bottom line is, I would not cut a hole in the case, as then you’ll basically have an air leak, and could have less ac performance, and possibly less airflow from the vents, as the air would have another hole to go out. If you have the tools, some sort of mechanical ability, and means to recover the ac, I’d do it yourself. Probably take a day to possibly a weekend for the average joe blows first time.

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Thanks! I have tools and skills needed, what I don't have is time lol.

doo dah · Mar 24, 2021

I ended up drilling a small hole that the probe would fit through and sealing it up with silicon pooky. I'll report back on how it works out, will be in the 80s down here this weekend so a/c will definitely be in use.

doo dah · Apr 19, 2021

I know that few, if any, look at these boards anymore but thought I'd post back results. Evap temp sensor didn't fix my issue, ended up replacing the a/c pressure switch on the high side by the compressor. A/c works again.