Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

What should my Low and High readings be?

lv6l on Wed May 28, 2008 3:48 PM User is offline

Year: 1994
Make: Honda
Model: Civic
Engine Size: 1.6L
Refrigerant Type: R134a
Ambient Temp: 75F

i have a 94 civic. ac is r134a. i have a gauge manifold. what should my specs be at to see if it's properly filled. My ac is blowing, everything works. The hose on the low side where I fill in the freon is super cold to the touch. but in my vent my thermometer reads no lower than 55F when outside is around 75F What could be the problem. I check my heater core vents, it's all closed tight.

Edited: Wed May 28, 2008 at 6:02 PM by lv6l

TRB on Thu May 29, 2008 12:25 AM User is offlineView users profile

24 & 213 at your listed ambient with 30% humidity.


When considering your next auto A/C purchase, please consider the site that supports you:

lv6l on Thu May 29, 2008 6:48 AM User is offline

should the compressor and motor be on with those numbers? thanks.

Chick on Thu May 29, 2008 7:48 AM User is offlineView users profile

Yes, those are the pressures while the ac is on . When off, they will both be the same pressure after they equalize, and that pressure will depend on the underhood temp..Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

mk378 on Thu May 29, 2008 10:42 AM User is offline

Double-check the heater water valve. It needs to fully close when you set the temperature lever to cold. Mis-adjustment of the push-pull cable that actuates the valve is a very common problem on Civics. If hot water keeps going thru the heater it will reheat the air on the way to the vents.

Sounds like the refrigeration system is working OK. The air should be as cold as that line is.

To measure pressures, set the A/C for maximum cold, fan on high, with fresh air in, and leave the car doors open so the car doesn't cool off inside. Rev the engine to 1500 rpm and hold it at that rpm for a while until the pressures stabilize.

lv6l on Thu May 29, 2008 4:19 PM User is offline

OK, i will give that a try. I almost forgot to mention. When i put in the freon, I pulled a vacuum to about -25 psi. So I started putting in freon when the pressure is in the negatives, should my readings still be 24 and 213?

mk378 on Thu May 29, 2008 4:32 PM User is offline

Yes. The important thing is having the correct amount of refrigerant by weight. Did you keep track of how much was going in when you recharged it? I think that model uses about 18 oz. There should be a sticker under the hood saying how much to use.

lv6l on Thu May 29, 2008 7:01 PM User is offline

Well my car never came with a sticker. Because it never came with AC. I took it off another car and installed it. I took a reading and here is what i got. The low side was 25-27. The high side was 180-185. They were all moving back and forth thats why I gave you guys the range it was moving. I don't think I did it correctly though. Let me know; this is what I did. I put the low side to the low side and high side to high side. I close the low and high side knob and I plug up the yellow middle hose. This is the only way I can get even a reading. Because when I open either side the pressure would raise to max. Again, please let me know if I did it correct. Thanks.

Oh I look on the capacity list found on this site from NAPA and it says my car takes about 19oz. I put about 2 full cans. So thats a total of about 24oz. Is this bad? And when I put in the freon I turn the can upside down. Please tell me all the things I'm doing wrong so next time I can learn from this. Thanks.

Edited: Thu May 29, 2008 at 7:04 PM by lv6l

mk378 on Thu May 29, 2008 10:04 PM User is offline

The high side will depend strongly on the temperature of the air entering the condenser. The pressures look fine.

Measure pressure with both manifold valves closed. The manifold valves are opened only in order to use the yellow hose to evacuate or charge.

Since you can lose about an oz switching a can over you don't have a full 24 oz in the system. It may have more than 19 but probably not enough to matter.

If you keep the rpm up and it's not extremely hot weather, the evaporator should get cold enough to cycle the compressor off. The vent temp should be near 40 when that happens.

bearing01 on Thu May 29, 2008 10:57 PM User is offline

Originally posted by: mk378
The high side will depend strongly on the temperature of the air entering the condenser.

...and also the air temperature and air moisture content entering the evaporator. I would use the 2.2 x Ambient air temperature (in *F) as a ball park rule of thumb, but don't use it as a guide to charge the system.

lv6l on Fri May 30, 2008 6:36 AM User is offline

Oh I see. I should wait for a warm to hot day to determine if my AC is useful.

Is it bad to charge in freon with the can upside down?

mk378 on Fri May 30, 2008 10:18 AM User is offline

In theory, charging with the can upside down puts liquid refrigerant into the suction line, which normally contains only gas. When this liquid reaches the compressor it could "slug" it, similar to having water get sucked into an engine's intake and "hydro-lock" it. This is capable of causing major damage.

In practice, it is almost impossible to get the refrigerant to flow in fast enough for that to happen.

You would have known immediately because a Sanden scroll compressor responds to any sort of abuse by literally blowing itself apart.

NickD on Fri May 30, 2008 11:41 AM User is offline

On my last Honda, road debris chopped up and deposited on the evaporator fins was a problem restricting the air flow. Something to check.

lv6l on Fri May 30, 2008 3:10 PM User is offline

When I bought the AC from the junkyard and before installing it I flush all hoses and spray/clean all fins that needed to be clean. I made sure air can be flowed through easily.

Today I tested my AC with a thermometer. Outside temp. is about 75F and at idle I can get it no lower than about 42F Does this sound okay? Should it be colder?

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.