Okay, so I recently purchased a 1987 F-150, 5.0 v8. The system has blown hot air from the start, but I figured it was just low on R-12 and needed to be refilled. R-12 being expensive, I decided to buy a retrofit conversion kit so the system would accept 134a. Yes, I know this isn't the best course of action for the long run; however I have read as long as all of the R-12 refrigerant and R-12 oil are evacuated, it shouldn't be too detrimental (Correct me on this if I am wrong). Having said this, I took the truck to an auto shop and had them vacuum out the system. I then immediately added 36 oz of 134a to the low pressure valve. As I was adding the refrigerant the compressor clutch would engage and then disengage every 10 seconds or so. The more refrigerant I added the longer the clutch engaged, but never stayed engaged for more than about 6-7 seconds before disengaging again. During this process the air felt colder at times, but then returned back to its original, hot, temperature. I left the shop and drove home thinking the clutch would engage if the truck was actually driven instead of in idle. Once I got home I then added about 2 more oz from a left over bottle of 134a. I then tested the pressure of the high and low sides of the system with a manifold gauge; however at this point the clutch wasn't engaging at all due to the fact that it only cycles on and off when I am adding refrigerant, so I assume the readings were inaccurate. Just in case this assumption is incorrect my readings were 33 psi on the lower pressure, and 140 psi on the high pressure.

The system calls for a maximum of 3 lb. 4 oz. of R-12, 85% of this is about 44 oz(85% to allow for a safe conversion from R-12 to 134a), so at this point I am about 6 oz under the limit, assuming there are no leaks in the system.

I then add about 6-8 oz of UV dyed 134a to the system in hopes of discovering a leak. I used a black light and ran the length of the system only to find no leaks. I am now at maximum capacity, the compressor clutch is not engaging at all, and the gauge on the 134a can reads the system is undercharged.

I have checked the air filter and condenser and both are clean, my accumulator is very rusted and looks like its in poor shape. Could a faulty accumulator be the source of the clutch not engaging? I am stumped, any advice or comments are greatly appreciated!

 

I am assuming you have a orfice tube cycling clutch a/c system.
you have no choice to retrofit as r-12 cannot legally be sold.
r-12 mineral oil is not compatible with 134a so pag oil must be used during the conversion.
its been a long time since I have done a conversion so I may have this wrong...I thought you had to add 10% more refrigerant not less? I guess you got your info from the conversion kit?




the clutch will short cycle when the refrigerant level is low.


so did the system hold a vacuum?
sure sounds like the system has a leak.


the best methods of leak detection for me has not been with uv dye and glasses or electronic leak detectors. I would fully charge the system them try a water/dish soap solution and spray it over every joint, compressor case and front seal, condenser and accumulator. with about 60+psi in the system something will bubble out. if you can access the evaporator look for a oily dirt build up on the surface. this is an indication of a mineral oil leak and dirt will build up on the oil.


when the leak is fixed, have it properly charged by someone with an a/c machine. the method you are using is not accurate.

 

1. You should have replaced the accumulator. The dryer/accumulator should be replaced any time the system is opened for service. It's possible that the Desiccant in the accumulator may be saturated with moisture and not releasing all of it when the vacuum is pulled. The moisture will cause the orifice to freeze up and the cycling you're seeing is being caused by the orifice freezing and un-freezing. How long did you pull a vacuum for? If I don't replace a dryer/accumulator, I always draw a vacuum for 1 hour after reaching 29.9 inHg on my gauge.

2. Your issue could also be caused by the style of condenser in your vehicle. An R-12 system uses a serpentine style condenser (High pressure gas into the top and high pressure liquid out the bottom), while an R-134a system uses a capillary style condenser (High pressure gas into the middle to fan across the condenser and high pressure liquid out the bottom). On the R-12 to R-134a conversions I have done, I change the condenser and rubber hoses (R-134a gas particulates are smaller than R-12 and can seep thru the rubber hoses used for R-12 systems). 0 issues doing this. Your serpentine style condenser may be causing too much of a pressure drop on the high side due to cooling capabilities (A.K.A. Super Cooling).

Depending on ambient temperature I would expect your pressure readings to be around the 30/210 reading if operating properly. The best way to check operation is to run the engine RPMs at 1500 RPM and place a BOX FAN in front of the grill set to HIGH. This helps simulate highway driving.