Hey so i got an 89 3.9l and recently my ac just isnt blowing as cold as it used to and im afraid it may be time to make the switch to r-134a. I've just seen a lot of different opinions on what all needs to be replaced. Some say everything needs to be swapped compressor and all, others say not necessary. Whats the deal? What all do i need to change? Thanks in advance.

 

What you NEED to change is the thermonic expansion valve and the receiver/dryer, after fully flushing everything.

The OEM design liquid line has a muffler on it; it should be replaced because they're hard to flush properly.

The original suction line is old, and may not be a barrier hose design, it should be replaced to keep from having a slow R134a leak through the hose or a failure of the hose, but then again, it might work just fine.

If reusing ANYTHING, use ester oil, not PAG oil; PAG gums up with mineral oil (used with R12), but ester can tolerate either PAG or mineral oil.

DO drain the compressor if you're not replacing it; I'd replace it if I were you, but then, it's not my money.

Replace ALL seals!

You can use the R12 low pressure switch, but you'll get better performance from a new R134a calibrated switch. Your choice, and since it's field-swappable without loosing refrigerant, you can wait on that. (Since the best price I found was around $135 for the R134a variant, I ran several years with the R12 switch.)

Reason for the switch is that R12's normal "low" side should be about 40psi; R134a, being smaller molecules, goes down to about 20psi for normal operation.

(That's also why some folks say to replace everything; R12 won't leak where R134a does, due to R134a being smaller molecules than R12.)

RwP

 

Awesome. Thanks for the extremely fast response. You haven't steered me wrong yet! Its much appreciated. I think ill go ahead and replace the compressor while im at it. I want it to be done right the first time. Thanks again for the help.

 

If doing that, do NOT forget to fully flush with A/C flush the evaporator and condensor!

Also, I'd recommend new hoses, due to the age; they may not be needed, but it's frustrating to rebuild a system with old hoses and find out that they leak due to age. Then again, that's me spending your money *grins*

Hint: If doing yourself, buy some Nylog(tm) and use that for the gaskets to seal better. is what I've been using the past decade (one bottle! A little daub'll do ya!)

Don't cheap out on the receiver dryer; Mopar and Murray are the only brands I can count on sealing. All the others seem to leak no matter what I do. Haven't tried ALL brands, though - GPD is not yet on my "Don't Ever Buy!" list.

RockAuto has a GPD compressor kit, with the seals, the thermonic valve, and the receiver/dryer (I'm trying that, I've not tried GPD yet. If it leaks, mutter mutter cuss cuss, I swap for a Murray unit.) A new compressor with all the fixin's was like $205 or so for a 1988. Add the 5% discount code and that just about covered slow boat shipping. (The kit with the reman'ed 4 Seizin's compressor was only $10 less ... with a $75 core!)

RwP

 

Bad news if you go for new hoses - nobody has the Four Seasons 55537 (other numbers also!) anywhere in the USA; that's the high pressure hose, the one most prone to leaking when it's not a barrier hose.

You may have to have that made by taking the old hose down to a competent pressure hose shop and have them remake it.

RwP

 

that is the correct way to do it.

My old 93 ford, I cheaped out and replaced the suction and discharge hoses as they were leaking....vacuum, added pag and charged it. Worked fine till the day I sold it 5 years later. This was an old beater car...I was not going to spend $1000 on it.