Automotive Air Conditioning Information Forum

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Unfortunately I'm back

Yesterday was the first time I took the car out on the road after doing the A/C work. The discharge air out of the vents didn't get as cold as I was hoping it would. Before I took it out I noticed I wasn't getting any water dripping out of the hvac drain, but thought maybe this was because it wasn't too humid that day? I drove it to my brother's house about 3 miles away, didn't get very cold, maybe cool at best. I let it run for a while in his driveway and noticed the compressor cut out a few times, my thought was the evaporator core was icing up and the deicing switch was kicking off the compressor. We came back to my place, hooked up the gauges and at idle I had 25/190, it was 83* ambient.

I thought I might have been getting some heat off of the heater core hoses or the water valve I replaced wasn't working correctly so today I unhooked the hoses from the heater core and looped the outlet out of the intake back to the water pump to keep from getting any heat into the heater core. I refilled the coolant system and took it for a ride. I had the temp sensor from my multimeter in the center vent and when I left I was getting discharge temps in the low 50s, when I went for a drive the temps never dropped. I pulled off into a parking lot after about 4 miles, held the throttle at 2000 RPM and felt the compressor kick off. I came home hooked up my gauges and got 25/210 psi at idle. I held the throttle to about 2200 RPM and the pressures went to 12/225 before the compressor kicked off.

I'm thinking it's low on charge and the evaporator core is freezing up, sound likely? If so I think I want to put more charge into it, but a full can will probably be too much. I think it was mentioned that I can charge by high side pressures and ambient temp, is that right? If so can you please tell me what that procedure is?

69DropTop wrote: I had the temp sensor from my multimeter in the center vent and when I left I was getting discharge temps in the low 50s, when I went for a drive the temps never dropped. I pulled off into a parking lot after about 4 miles, held the throttle at 2000 RPM and felt the compressor kick off. I came home hooked up my gauges and got 25/210 psi at idle. I held the throttle to about 2200 RPM and the pressures went to 12/225 before the compressor kicked off.

I'm thinking it's low on charge and the evaporator core is freezing up, sound likely? If so I think I want to put more charge into it, but a full can will probably be too much. I think it was mentioned that I can charge by high side pressures and ambient temp, is that right? If so can you please tell me what that procedure is?

I think that you're low on refrigerant, from your pressures at 2000 rpm. Your vent temperatures are getting there, but quite marginal for an 83F day. I would add 1/2 can refrigerant (no sealer) and see if that helps get the high side to about 260-280 psi at 2000 rpm, and add remaining half if the high side is still too low at 2000 rpm. Remember to purge the gauge lines when doing this.

The compressor did NOT shut off due to high pressure, wonder if it shut off due to LOW pressure, because 12 psi low side is real low.

Cusser, thanks for the reply! Is your name cusser because whenever you work on a car like my you call it every name in the book?!

I thought the pressures seemed a little low. My car is a '69 Mercury Cougar and I'm using R12. The only thing that I know of that cuts the compressors on these systems is a deicing switch mounted in the hvac box that has a sensor of some sort inserted in the evaporator core.

According to the forecast it's supposed to be 85* today so I will do what you said, put more refrigerant in until the high side hits 260-280psi at 2000 rpm and I will be sure to purge the service hose where it goes into the gauges.

Are those the pressures you mentioned what I should be looking for using R12?

This would be a lot easier with a sight glass, but someone already fixed that for you.

It may be a little undercharged. Your 12psi low side makes it look that way. If it was an orifice tube system I would say the OT was too small.

You can add small amounts of refrigerant while looking at the pressures to sneak up on a full charge with a TXV system like that.
On a custom system where the charge level is only a guess I handle it like this:

Watching the high side with it idling & the cabin fan on low, add a half ounce of refrigerant to the low side & wait for a minute. Did the high side stabilize at the same pressure? Or 1 psi higher? That means the refrigerant is being stored in the Receiver as liquid, where it takes up very little space.

If you add 0.5 ounces + 0.5 ounces + 0.5 ounces, and see little or no high side rise, it is still stacking up in the receiver & the line from the condenser.

If you see a 5 psi rise with only a half ounce of refrigerant, it is filling the condenser itself. This is the "spike" One should recover the charge at that point & weigh it. Then deduct an ounce & use that for a charge spec.

The problem is you only know what "enough" is, by going too far...

Add a little refrigerant, monitor pressures & the vent temps. Remember to let the system stbilize for a minute after adding. Log the resuls & post them for us.

Okay, I will do the procedure as you mentioned and post up the results.

I was wanting to put dye in the system. One guy told me he injected it into one of the hoses using a hypodermic needle. Is that an acceptable way to do it? Looking back I wish I would have just put a quarter ounce of the liquid dye into the compressor when I added the oil, but too late for that now.

Uh, do NOT poke holes in refrigeration lines!

That has to be the worst "fix" I have heard in years.

There are various tools to add dye or oil to a charged system.

You have a York. 45 years ago we serviced the oil in those by isolating the charge in the system with the valves. Front seat the suction / run the pump to vacuum on the suction side / stop the pump front seat the discharge valve. Then when you pull the fill plug you get a little puff of R12. No big deal in 1973. After you serviced the oil, you cracked the low side valve to get a little refrigerant purge for the crankcase, and put the plug back in. Top up the charge with the sight glass & send the happy customer down the road. We replaced compressors the same way - not a vacuum pump in sight.

Now, after posting that History Lesson, I have to tell you that this is no longer acceptable, that every molecule of R12 must be recovered in an approved method - or the Polar Bears will burst in to flame.

Yeah I felt a little weird about poking a hole in one of the refrigeration lines so that is why I asked before I did it, glad I didn't do it! I did see in the factory service manual that they describe a procedure similar to what you said. What do you think is the best way to inject dye into it now? I do have a tool that is an oil injector that goes midline that I guess I could use?

Yes, the pressures I mentioned are appropriate for R-12 (I still have one R-12 truck myself).

I've only added UV dye to ANY vehicle by pouring some in when the system was still open, or by adding a can of refrigerant that also contained UV dye (no sealers !!!) to the system.


AGREE - poking a hole in a refrigeration hose to add dye is probably the WORST idea I have ever heard !!! Last summer my 19-year-old Frontier developed a pinhole in its high pressure rubber hose, and I had to replace that.

"The only thing that I know of that cuts the compressors on these systems is a deicing switch mounted in the hvac box that has a sensor of some sort inserted in the evaporator core. " That - and a pressure switch on the receiver-drier on my 1988 Mazda truck.

Last night I got the UV light and looked over the system. When I first looked at the prestite tape I put on the expansion valve it was glowing green which was very concerning to me, but I cut a piece off of the roll and it glowed green also so I guess that is just how it shows up under the light. I looked everything else over really well and I noticed the suction line, that appears to be factory from '69, the front half of the length of the hose was glowing a dark green and towards the compressor had a few spots that were brighter green, more like what I would expect the dye to look like.