Explain this

[Helirich]

I put 500 miles on the car yesterday. Most of the time I was driving 65-75mph. My water temp was reading 160. The sender was recently replaced and tested to be fairly accurate. It was hot out and I had the AC on max. My AC works pretty good and I was comfortable.

I came to a slow down on the highway due to an accident. During the slow down, I was going about 15mph for 20 minutes. The water temp slowly crept up to just below the 220 mark and stayed there. OK, that makes sense because there's less airflow at the radiator. Here's the strange part, my AC started blowing ice cold. It started fogging the windows and giving me a chill to the point where I had to turn it to "norm".

So if the radiator is getting less flow, why wouldn't the condenser get less?

BTW, when I got back up to 70mph, everything returned as before the slowdown. I had to turn the AC back to max. I hit another traffic jam later and the same thing occurred.

[Bitsyncmaster]

Your probably icing up the evaporator at high speed and when you slowed down the ice is melting (thus the vapor from the vents) and then the AC works better without ice.

[Ron]

Did you ever charge the AC by weight?

[Helirich]

Your probably icing up the evaporator at high speed and when you slowed down the ice is melting (thus the vapor from the vents) and then the AC works better without ice.

When the evaporator ices up, you lose airflow out the vent. I didn't lose any air flow. why would ice melt at slow speed anyways?

Did you ever charge the AC by weight?

No, I haven't touched it since getting the glass tinted. (It has worked good) I want to pump the whole system down and change the accumulator/dryer. Now that it's working, it's on the back burner.

PS, the AC did the same thing today on a slowdown. Very strange, but I don't have time to fix what isn't broke.

[DMC-Ron]

When the evaporator ices up, you lose airflow out the vent. I didn't lose any air flow. why would ice melt at slow speed anyways?

If the evaporator completely iced up you would notice the change in airflow. Many times the icing is a just at the front end of the circuit and doesn't change the airflow enough to notice. However, it does reduce the effectiveness of the evaporative coil which elevates the discharge temperature. At lower car speeds (reduced condenser air flow) the working head of the compressor increases because the difference between evaporator and condenser temperatures increases. This melts any ice that built up. Once you're back to road speed (higher condenser air flow) the compressor head decreases and ice can build. There are several things that can cause evaporator ice. Low refrigerant charge is one possibility. In our DeLoreans, an increase in the cycling of the compressor clutch can be a symptom of low refrigerant. But you need to have a feel for the system because it's normal for compressor cycling to change with ambient (ie cooling load). Hotter temperatures decrease the cycling (longer on times). Cycling (and off time) increases as the temperature is milder (less load). Based on your description, you're ok for now. When you do the planned work on the system you can recover the refrigerant and recharge with the exact weight.

Ron

[Helirich]

If the evaporator completely iced up you would notice the change in airflow. Many times the icing is a just at the front end of the circuit and doesn't change the airflow enough to notice. However, it does reduce the effectiveness of the evaporative coil which elevates the discharge temperature. At lower car speeds (reduced condenser air flow) the working head of the compressor increases because the difference between evaporator and condenser temperatures increases. This melts any ice that built up. Once you're back to road speed (higher condenser air flow) the compressor head decreases and ice can build. There are several things that can cause evaporator ice. Low refrigerant charge is one possibility. In our DeLoreans, an increase in the cycling of the compressor clutch can be a symptom of low refrigerant. But you need to have a feel for the system because it's normal for compressor cycling to change with ambient (ie cooling load). Hotter temperatures decrease the cycling (longer on times). Cycling (and off time) increases as the temperature is milder (less load). Based on your description, you're ok for now. When you do the planned work on the system you can recover the refrigerant and recharge with the exact weight.

Ron

On one hand, I have experienced iced up evaporators on many vehicals, including the Delorean and I have always noticed a decrease airflow. On the other hand, I have to admit, this does explain what's happening. Thanks for posting.