Automotive Air Conditioning Information Forum (Archives)

vcsmike on Wed July 31, 2013 4:19 PM

Year: 1982
Make: Alfa Romeo
Model: GTV6
Engine Size: 2.5
Refrigerant Type: R134a
Ambient Temp: 95
Pressure Low: 25
Pressure High: 295
Country of Origin: United States

After upgrading this system, I am not satisfied with its performance, but the system's behavior has me confused. It seems to perform better sitting at idle than it does when the car is moving. I had 48F at the vent when I finished charging, but when I drove the car, the vent temps went up to 62F. Normally, old Alfa A/C systems struggle to cool at idle.

The system was originally a 2 lb R12 system with a mini-York compressor. Here is what I replaced/upgraded:

New Sanden-type rotary compressor
New parallel flow condenser that is larger than the original
New R134a expansion valve
Changed poor performing GTV6 radiator/condenser fans with better performing fan from a Milano
All new hoses
New receiver dryer
Replaced original pressure switches with a trinary switch wired to radiator fan relay (GTV6's were not set up this way originally)
Flushed original evap
Compressor came with a full charge (about 5 oz) of PAG (forgot the weight)

I pulled vacuum, & initially charged with 1.8 lbs of 134a. Vent temps were around 62. Added an ounce at a time until it was blowing 48F out of the vents. I was at 35 oz. However, my high side was too high, & I was tripping the high pressure switch when I revved the motor. I removed some of the charge. I would estimate that I'm right at 2 lbs right now. When I rev the motor, the high side goes up near 400 but doesn't go high enough to trip the pressure switch. The low side drops to around 15 & then pops back up into the low 20s. When I drive the car, I get low 60's from the vents. It cools better when I'm sitting. The suction hose is sweating all the way to the compressor, but it's not sweating a lot.

I've verified that the heater core isn't getting any hot coolant in it. The valve is fully closed, & I have a manual shut-off valve on the return side. I can touch the flange where the valve connects to the heater core, & it is cool to the touch at a hot idle.

I an concerned that I might be getting outside air through the system. There is a slide lever that controls this, & moving it makes no difference. However, I don't think this sufficiently explains why my low side is so low.

Something else that is strange. The interior HVAC box is a very compact setup. The evap, heater core, & blower motor are in one box under the center of the dash, & it houses two vents. The blower has dual fan blades similar to an old Suburban's rear A/C blower, & one blade pushes air out of each vent. Despite this very compact setup, one vent blows about 5 degrees colder than the other.

Any input would be greatly appreciated.

-------------------------
Michael Keith
Vintage Car Solutions
Houston, TX

webbch on Wed July 31, 2013 5:49 PM

I'd suspect the low, low side pressure is a result of the TXV being wide open....did you insulate the bulb (prestite tape, sometimes called cork tape) when you installed it? Just wondering if the reheat from the outside air is keeping the bulb warm as a result of not being insulated, and hence keeping the TXV wide open, and hence the low pressure.

BTW - your math on the amount of refrigerant doesn't add up

vcsmike on Wed July 31, 2013 6:04 PM

Pulling the center instrument cluster gave me enough access that I was able to verify that the recirculating flap is closing. I still might be getting outside air due to poor sealing. I couldn't see in there very well. As to system pressure issues, the TXV would be a good guess. It's brand new, & I've never had a bad one before. Guess there's a first time for everything.

As to charge level, please be more specific as to where you think I've gone wrong. Original system is 2 lbs (32 oz). When converting to 134a, I reduce the charge by 10%, which gives me 1.8 lbs (28.8 oz). I started with 1.8 lbs, but it was blowing 62F out of the vents at idle. I added more because of the larger condenser, & I added 1 to 2 ounces at a time until the vent temps stopped dropping. I stopped at a total charge of 35 oz, & I had 48F out of the vents at idle. However, my high side was high would spike up when I revved the motor. This was causing the high pressure cut-off switch to open. Therefore, I removed some of the charge until this condition subsided. I can only estimate the amount that I removed, & I believe I removed around 3 ounces. This would put me right back at 32 ounces (2lbs).

Thanks.

-------------------------
Michael Keith
Vintage Car Solutions
Houston, TX

webbch on Wed July 31, 2013 6:08 PM

You're right on the math. Having a senior moment I guess....

vcsmike on Wed July 31, 2013 8:21 PM

I've started having senior moments well ahead of schedule. The charge level was something that I was a little uncertain about since I changed refrigerant type, condenser type, & condenser size.

BTW, forgot to mention that I did wrap the TXV thoroughly in new cork tape.

-------------------------
Michael Keith
Vintage Car Solutions
Houston, TX