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Blowing Hot

ArizonaHeat55 on Thu July 17, 2008 2:57 PM User is offline

Year: 1991
Make: Honda
Model: Prelude
Engine Size: 2.0
Refrigerant Type: r-12

Well i just bought the car and it blows hot when I turn the AC on. I wanna check if the compressor clutch is good and enaging, how can i do this. I checked the heater valve and it seems to close all the way so i dont think thats the problem. I dont have the ac gauge but i wanna check everything else before getting one. Is their a way for me to hear if clutch is engaging. I have voltimeters to check if voltage is getting to the compressor but i dont where to put terminals to. Also ive heard of people adding r-134 and adding oil and their a/c works good even though it was r-12, has anyone done this before?

Also i dont know if anyone knows in my particular car if the clutch itself can be replaced with out changing the whole compressor.

The car is a 91 Prelude...

Thanks in advance.

Chick on Fri July 18, 2008 7:07 AM User is offlineView users profile

Your system may be empty, you need gauges to check that first, you should also be able to see if the compressor engages, but of course you will need refrigerant.. Check out the FAQ page of the forum for proper retrofit, vac/charge procedures, hope this helps..

PS: You cannot just add R134a and oil without evacuating, thats what we call death kits.. You can't have any air in the system, and it must be charged correctly or the system will be destroyed..

Email: Chick


Freedoms just another word for nothing left to lose

mk378 on Fri July 18, 2008 8:44 AM User is offline

If the compressor doesn't engage, check the system pressure. When you don't have gauges you can check the pressure switch. I think it will be on a refrigerant line near the front of the car, in a block with a sight glass. Unplug the switch and check for continuity. If the switch is open it's a very good bet that all the refrigerant has leaked out.

ArizonaHeat55 on Sat July 19, 2008 12:45 AM User is offline

Well i got gauges, but the problem is the high valve fitting is a little smaller then the low one i think its like 3/8 i wanna know where i could get an attachmet so that i could check the pressure on the high. Also your right about the pressure switch being closed but i bypassed the sensor and the compressor clutch worked so now its probably that it needs freon or the dual pressure switch isn't working but most likely system is leaking.

I wanna know where I can get the atachments to check for pressure on the highi thinks its a 3/8 fitting and the low one seems to be 7/16.

Thanks In Advance.

mk378 on Sat July 19, 2008 8:42 PM User is offline

Most "real" parts stores sell the adapter you need. It's "3/16 flare" (same size used for 3/16 OD metal tubing with a flare nut) which is a 3/8 thread.

You can tell if the system is empty just by putting the low side hose on. While the compressor is off, both pressures are the same.

Legend on Mon July 21, 2008 3:05 AM User is offline

I have a similar car: 1990 Acura Legend, 2.7 engine, R12, and similar problem.
I got the gauges hooked up, engine revving at 1500 RPM, AC on, Fan on at max speed. Here's the report.

Weather: 90F
With AC off: pressures from both lines 80 psi
With AC on: low side line 0 PSI, high side line 115 PSI
Eventually, the low side line became very hot, instead of frosting (could feel gas/fluid moving inside the tube). The high side line was luke-warm to touch. Air from vent was hot, even hotter than air when the heat was on in the winter.

What do all these mean? What component is shot: expansion valve, evaporator, or condenser? Thanks

Chick on Mon July 21, 2008 6:18 AM User is offlineView users profile

You should have started your own thread, more people would check it out.. anyway, 90 degree day, static pressure of 80 means the system is just about empty, thats why the low side dropped to zero.... Until you fill it you won't know how the system components are working. Have the system evacuated, change the drier, then recharge with R12..If you are going to retrofit to R134a, start a new thread and you'll get all the help you need right here..Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

Legend on Mon July 21, 2008 7:27 AM User is offline

Thanks Chick for the quick response. I'll start a new thread next time.

From what I googled, the static pressure should be between 35-50 PSI and it only takes 20 PSI to get the compressor going. Besides, I could feel the gas/fluid flowing in the low side line and there were no bubbles in the sight glass with bubbles indicating low freon. What is the normal static pressure for the R12 system? I'm confused. And why was the low side line hot, instead of frosting?

I intend to stay with the R12. I heard it's just way better than R134a.

Chick on Mon July 21, 2008 7:42 AM User is offlineView users profile

The static pressure should be close to the ambient temp, don't have the pressure temp chart at home, but if you can find a shop that will recover and weigh the charge, that will tell you just how low it is. If the low side goes into a vacuum, there could be a restriction, and the lines in and out of the drier should be the same temp, if it's cooler coming out, the drier filter is clogged..Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

Legend on Mon July 21, 2008 8:20 AM User is offline

Thanks again Chick. I'll find a shop that will recover the precious R12.

I didn't feel the lines immediately in and out of the drier. The line that was hot was the one with the port to which I attached the pressure gauge and with the insulating rubber. I'm not sure whether this would make any difference in your assessment.

btw, I just notice that the ambient temp sensor is missing. Does it affect the AC system in anyway? Thanks

Edited: Mon July 21, 2008 at 8:25 AM by Legend

NickD on Mon July 21, 2008 8:57 AM User is offline

Big time if the ambient temperature sensor is used like in other automatic climate control systems that tells the computer when the compressor can run. Has a very high resistance when it's cold outside, and missing will tell the computer it's damn cold outside. Seeing a clear sight glass with a none running compressor doesn't tell you anything.

Do you have a circuit diagram of your AC system? I don't, but would be the first thing I would look at, can get one for

Legend on Mon July 21, 2008 9:23 AM User is offline

NickD: I don't have the circuit diagram for Acura but how will that help me diagnose the problem?

Thanks for the info about the ambient temp sensor. Despite missing the sensor, the compressor was still running, the clutch did engage. Although I didn't see bubbles through the sight glass, I could see fluid moving around in there.

So, is the problem low freon like Chick said or missing ambient temp sensor or something else?

Legend on Tue July 22, 2008 6:27 PM User is offline

I checked that my AC system doesn't need an ambient air temp sensor. Anyway, the problem is indeed low level of freon. Thanks for all the help.

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