toomuch4u_2

We are working on my 73 and we thought the AC was low on freon, however after being a bit low, we added more to get it to the standard levels, but still NO COLD AIR. Compressor is engaging and running, and the freon levels are good, but again, still no cold air. Any thoughts?

terry82

you need to put a set of gauges on it to see where you are at .is it r-12 or 134?

toomuch4u_2

Converting to 134....we have a gauge on it...?? any thoughts?

terry82

vac it out ,change the oil ,put in the 134a and tell us what you .

I'm Batman

It sounds like the coolant isn't circulating through the system properly. Has the compressor been rebuilt?

Vette5.5

You mentioned a gauge, but you're really wanting gauges on both low & high pressure sides of the system. Good idea having a temperature probe on the suction line(big tube) leaving the evaporator, as should be cool. Having a temperature/pressure chart handy's a good idea, as shows where the pressures should be, relative to temperatures. Could go on about metering devices, superheats and such, but if not familiar, best having a shop service it.

Jud Chapin

Yes, you'll need pressure readings from gauges for both the low and high side to determine the problem.

vr3.9

Yea you need to put the gauges on so you can so what both the high and low side are. If the difference isn't great enough it won't cool say 40 and 190. Varies on outside temps. If the difference isn't very much then your compressor is weak. If you see a large difference and it still doesn't cool it's probably your expansion valve.

redwingvette

If your system still has a VIR valve then that may be the issue. They are setup for R12 and may need to be reworked for R134.
I completely replaced my system last spring.

I'm Batman

1) Unless you have an NCRS car, rebuild the system to the late C3 spec.
2) Get a POA valve that's designed for R134A.
3) Get a proper high/low manifold gauge set.

toomuch4u_2

Thanks for the direction... I will work on. Appreciate it.

L84s R Us

Batman seems like he has it. I have been helping people get their A/C/ systems up and running on this forum and another for years. The biggest and most common mistake people are making is not using an original POA valve. If you car is still having issues, you can have you original POA valve adjusted for 134 at a A/C shop.

If you have any other questions PM me and I will start from scratch with you if you like.
Does the reciever dryer have a sight glass?
Best of luck

chevymans 77

The system once converted correctly will cool as is if all components are in good working order.

The system will work its best if you keep the POA valve in place. It requires more maintenance and system preparation but is the best option for a better performing system.

The pressure/temperature relationship of R12 and R134a are very close and don’t require any changes to make the system cool. You can improve the performance of the system by performing some upgrades like the adjustment of the POA valve operating pressure and installing a cross flow condenser but the system will perform very well as is if the system conversion is performed correctly.

The fact that he indicates the system does not cool at all is a good indication that there is another issue other than an adjustment to the POA valve.

To correctly diagnose we really need to know what the operating pressures are and how much refrigerant has been added to the system along with the operating conditions of the vehicle (idling, what settings at the AC controls etc…..).

Neal

L84s R Us

Yes, I get that Chevyman.
That is why my last question was "Does your reciever dryer have a sight glass"
Chevyman, you seem to have a pretty good grasp of what is going on with this car. I will bow out of the way and let you help him fix it. Should be nothing to it once you know a few things.
It is always much easier to get advice from just one person.

If by chance you need any parts, I have boxes and boxes of old A/C stuff. Anything you may take off, do not throw it away.


Best of luck guys,
M

Some things are very minor. To be honest: when I put the A/C back in my 72, 454 car, back in the 80's, my only problem turned out to be that I did not change the dial on the console to cool. I was just learning back then, but I have never made that mistake again. What I learned was, sometimes it can be that simple, or the cable is not moving the damper.

chevymans 77

L84s R Us:

Please don’t take any disrespect from what I posted. I was only trying to add to the responses that have already been posted. We all appreciate the help offered hear from the knowledgeable members.

We all have different ideas of what to do when an issue comes up here on the forum when a member asks for help with their car.

The op was asking questions about him adding Freon but the results were not what he was expecting (cooling). Some responses were to replace components that may be performing correctly but without more info we really can’t offer good guidance on what the next step may be. Allot of the responses are from personal experiences that we may have encountered with our own cars or of someone we may have been helping at the time but we really need to have the operating conditions of the AC system at the time he was working on it to truly trouble shoot and offer help.

I would recommend he contact you and take you up on your offer and if yawl need further help post here and we will try and help.

Neal

L84s R Us

no disrespect taken. I honestly think it is easier to deal with one person on something like this. To me it sounds like a minor thing, but figuring out the minor thing is the problem.
The reason I mention the POA is, a lot of guys use the POA eliminator and find out later that that is NOT the way to go. Just wanted that in his brain.
He will figure out what works for him. It is just really easy to get overwhelmed when you have a bunch of guys throwing words at you that you do not understand.
Dealing with one person often makes this much easier to deal with.
Between us all, we will figure it out.
Take Care,
M

Tphoodpack

Dear sir,
I have a 77 vette and ac not working. Blows cool but not cold. Still has r12 ? I was considering converting to r134 while trying to fix it. Everything seems to work fine just not very cold. Where should I start and should I convert to 134 first. I didn't want to keep 12 if going to not work anyway, but adding some 12 may be easiest for now. Please advise. Thank you for your advise.
Sincerely,
Tom
Biloxi, MS

'75

An easy check to determine if the charge is low is to locate the sight glass. It's located just under the fender lip in the passenger side in the liquid (high side) line. There is a pressure switch in the same location. Start the engine and run the AC till it stabilizes, 10 minutes or so, look at the sight glass and watch for air bubbles flowing past it. On R12 systems, when the charge is correct, you will see a small bubble pass the sight glass every few seconds. If its all foamy looking, you likely need more r12.

alvinjvillalba

The reason for no cold air with all the things intact is due to the DUST that oftenly get stuck in AC vent. Also, please check that the exhaust is working fine.

I hope this helps.

20mercury

Thought for you, assuming the high/low pressure checks out good, I would check to see if your condenser and evaporator are all super clean. The "suit case" or casing for the evap on the firewall on mine was full of leaves, 40+years of trash, ect. If all else fails, take everything out and clean it, you can buy a cleaning fluid for condenser and evap coils at NAPA. Again assuming your compressor and VIR are working. Here is a good a/c forum too.

http://www.autoacforum.com/

Hope this might help. BTW, Harbor Freight sells gauges and a vac pump that got the job done for me.