I bought an A/C thermometer; the kind you stuff into the vent, and I'm keeping track of the air temp.

The last couple of days here have been in the low 90s so its a good time to check it. I'm making measurements with the engine cover on and off as my theory is that the engine cover traps heat. I am making measurements in both recirculate and fresh air mode, but so far there seems to be little variance in temp.

With the engine cover on:
Idling in traffic = 50 degrees
Highway at 80 = 40-42 degrees
Feels like less CFM (cubic feet / min) of air from the vents

With the engine cover off:
Idling in traffic = 46-47 degrees
Highway at 80 = 40 degrees
Feels like more CFM from the air vents

In my garage, the compressor duty cycle is:
On for 10 seconds
Off for 5 seconds

I'm going to put this into the punchlist I am compiling for the Dealer. Data never hurts.

Chrisbert

 

Do you have the new AC control box, or not?

I just can't see how the engine cover would affect AC. It's mostly about how effective the condensor is - that's the AC radiator that's in the nose of the car in front of the radiator.

As far as "CFM" or how much air volume you're getting out of the vents - that's typically only affected by whether or not recirc is on and what fan speed you pick.

BTW, my '90 RX-7 convertible has about 34 degrees coming out of the vents . The 2nd gens had some COLD damn AC, when it was actually working and all the freon hadn't leaked out .

Dale

 

I don't have the AC fix yet. One thing I noticed in the garage was the duty cycle of the compressor and its relationship to the main cooling fan.

I can hear 2 fans in the front of the car. One is significantly louder and beefier sounding so I figure it is the main cooling fan.

When the compressor engages, the second smaller fan comes on. But here is the weird part. If the other fan comes on while the compressor is on, it shuts off when the compressor does. I'm not sure why; just seems they should be unrelated.

I too find it odd that the engine cover could have any effect, but it seems to. I don't have a meter to measure CFM so my statistics are subjective there.

My neighbor has a very old RX7; 90-92 model. He and I were talking about it and he said that on fresh Freon it would literally freeze your face. He said it was about 34 degrees. I attribute that to the pre-ban freon most likely. The kinder-gentler refrigerant (Freon is a trademark of DuPont) we use today just doesn't get as cold.

 

I had my car in for the new AC amplifier due to lack of cooling and the cool/cold circulation issue. I live in Fresno CA so I get the 100 degree heat here all the time and its frustrating. I also recorded stats on the performance of my AC unit before and after the half fix. At idle will be 55 to 58 degrees F, and on freeway at 75 mph it would get to 48 to 44 at best. After the AC amplifier was put in, idle would be at 52 to 55 and on freeway 40 to 45. It gets a bit colder after the install but the circulation between cool/cold/cool is still a problem and I think this is what is keeping the car from cooling properly. I still sweat in my car with a tshirt, I do have the leather seats, but still I think they didnt replace my AC amplifier, they just said they did. Some dealerships are full of crap.

 

This is a good thread. Interestingly enough, I've had a thermocouple in my dash all this week during my commute to see how the AC stacks up with numbers. During the AC performance test (speed=4, recirc, coldest setting, 1500rpm, t-couple in center vent), I was getting temps cycling from 46-55 at ~87 ambient. This just barely fails the expected performance curves in the manual, so I started taking more measurements. On the whole, if just idling, my car likes to be 50-55, and when you kick the revs up for the test, you start dipping to the mid 40s. On the freeway, at fan speed 4, 93F ambient, recirc, it blows between 45-60. A pretty rediculous swing (not cutting the compressor out due to throttle) IMO. The lowest I've recorded was 36-37 (ambient 82) after I cut the fan speed down to 1 after being on FS4. These are my numbers FWIW (they'll be in table form soon for the dealer), and I HAVE had the AC amp replaced - it was obvious, the AC actually does different things than before (kicks on recirc at full cold automatically).