Another a/c question

[Tim the Teacher]

Had the high side tube replaced after my intercooler rubbed a hole in it. I drove the car with no air for a year before repair. I now have 55psi and the condensor cuts on and off appropriately but I still am not getting air that is very cold. Could it be that this 101 degree day is just too damn hot for a Miata a/c to cool great or could there be another problem. No leaks detected....

[trickyrix]

Could it be that this 101 degree day is just too damn hot for a Miata a/c to cool great or could there be another problem. No leaks detected....

DING DING DING! Winner winner, chicken dinner! My A/C has been struggling as well - even with tinted windows...

[POS Racing]

What is the pressure spec for the car??

I'm thinking Rick is on to something with this heat! Stupid heat......

The gauge I used shows 55psi being a bit high. But YMMV

[cliff]

I have a 1991 model with A/C problems and appreciate any and all suggestion(beside "take it to an A/C shop", that is my last resort) The compressor will not kick on, I jumped the wires that plug into what I think is the low pressure switch(two wire connection on the high pressure line) with no luck. i also traced the wires from this switch and they go to the right cooling fan. I pressed the valve on the low pressure line and freon comes out, I know it could just be low on freon but I want to try and get the compressor to kick on before going to A/C shop. Any ideas?

[onething]

Back to the original question: IIRC you should only expect the AC to cool the air about 20* lower than ambient temp. Make sure you're on recirculate so you aren't trying to cool the outside air and it should help. I find pointing the vents at the top makes it cool more quickly since hot air rises.

Spiffy beaded seat cushions help too . . .

cliff, I'm pretty sure low pressure will keep the system shut down. Does your system have a sight glass, and can you see anything moving through it? I know a really good AC shop in Burleson.

I have now exhausted my AC expertise, and I haven't stayed at a HI in over a month.

[Radio-Active]

It used to be easy with a sight gauge in the system. You just filled until it quit blinking. You should also raise the RPM around where you will be at while driving the car to get an accurate reading.

Here is the pressure temperature chart link. 40* is usualy where you would want it approximately.
Linkie:

[Tim the Teacher]

I went back and put it on the gauge just now and it reads 43. I read the gauge yesterday while I was pushing down on the applicator.....duh. It also is much colder as the car is sitting in the garage with the tailpipes outside. I hate Texas summers.

[motorollow]

My AC is pretty cold in this heat. Hudson Hawk put an aftermarket aluminum radiator and fans on my car when he had it. My temp gauge actually drops slightly with the AC on and both fans running. I have no problems sitting in heavy traffic after work when its 100 outside.

[jrj512]

I just used my AC in a mix of highway and stop and go driving. While I was not shivering, I was comfortable with the fan on high and set to recirc.

[gabkwong]

I just used my AC in a mix of highway and stop and go driving. While I was not shivering, I was comfortable with the fan on high and set to recirc.

+1

[carguychris]

What is the pressure spec for the car?? ...The gauge I used shows 55psi being a bit high. But YMMV

55psi also seems high to me. It's hot outside, so the pressures will run high, but the low side should be showing 35-45psi @ ~1500rpm under the current weather conditions. (EDIT: Just noticed the new reading of 43psi.)

Your system may be overcharged, in which case the high-pressure shutoff switch may be cycling the compressor off prematurely to protect it from damage. A/c systems need just the right amount of charge to work properly; a little too much is actually worse from a cooling standpoint than a bit too little.

I'd recommend renting a real gauge set with both high and low pressure gauges and getting readings with the rpm just above idle (1200-1500rpm). Assuming you have an R-134a system (not sure what year your car is), the high-side pressure should be 2.2 to 2.5 times the ambient temperature (220-250psi), and roughly 5.5 times the low-side pressure (35-40psi). If the ratio is right but both pressures are too high, you have an overcharge. As I implied before, this will usually also result in the compressor shutting off frequently.