My air conditioner seems a bit on the weak side as far as blowing cold. I stopped today as it got very warm(upper 70's) and the air didn't seem to be working at all. Found out I had an electrical plug on the hi pressure switch was disconnected. Fixed that then pressure tested it. The guy said it was where it should be,maybe a bit hi. (55 lbs on the gauge). It blows a little cool air but not strong. Is this common or do I need to tear into it and check for blockage of some sort? I fixed the hi setting on the fan with a new fusible link so its blowing on hi, just not what I would expect.

 

The vettes never had very good air conditioning. I bought a brand new 74 and took it back to the dealer numerous times because it didn't blow very cold. GM had them wrap the tubing in the engine compartment, it didn't help much,they checked the freon charge that was ok. I had to always run it on high when it was hot, even on the highway. GM didn't really care they had people in line waiting to buy vettes in those days. I had to put my order in July of 73, and I didn't get mine till Feb of 74 they only were allowed to sell 11. And I was an employee of the dealership,how times have changed now they have them sitting on the lots.

 

I think maybe I'll try and open it up and see if I can do some "home improvement" Not bubba style mind you.

 

If your pressures are correct, take a look at the seal on the rear of your hood. If that is in bad shape, engine compartment hot air will get into the ducts and warm your a/c's cold air. These cars, if everything is in order, will blow cold air. My '76 is 40 degrees at the vents, and I live in South Fl. The main problems with these cars is insufficient air flow, but they still do an adequate job.

 

Warm air gets in around the side on the passenger inner fender by the firewall. Also, your drier may need to be replaced,I would suggest a flush and fill to get any trash out of the system, and make sure your fan clutch is working properly.

One final thought, the ducting behind the dash has a large gap that GM wrapped duct tape around. Over the years, that duct tape gets old and falls off, leaving a huge gap.

Maybe pull the passenger knee pad and inspect it.

 

Just a thought, the old Harrison compressors weren't the best in the business when they were new. What about switching to a newer style compressor?

 

Also look in the area of the windshield for a fresh air door that is vacuum controlled. It closes when a/c is on max thereby not permitting outside air into the system. I ran a vacuum line to mine to keep it closed permanently. Every little bit helps. Also check that hood to cowl seal.
Good luck

 

There have also been posts about insulating the airbox in the engine compartment. Also changing out to a C5 fan which blows more air. This requires a spacer. Check the old posts.

 

At 70 degrees 55psi is too high. Connect a guage set so you can read both low and high sides, and see what you have. Do you have frost on any of your piping? Depending upon the readings you may have several possibilities like: too much charge, air present, heat sensing tube, defective compressor. Guage readings will narrow your problem down.
Cheers
Tommy

 

I think that's a C4 fan you mean.

 

Newer compressors are more efficient,they dont rob as much HP as the old A6 compressors. But the old A6 (the long fat compressor) could cool a house. The R4 compressor ,flat round style, were the worst of the bunch. But they still did a great job

 

i am a a/c technical, i recomend to make a inspection on the duckts,and air box located on the engine also is pocible the orifice tube can be cloged whit any garbage from the sistem on thease cases we fluch the sistem complete and replase the drier ,orifice and oil ,when you use 134a on a old sistem we recomend a secondary fan but is exept of the ouner . good luck

 

Your system will work fine when repaired correctly. GM used basically the same components on the AC system in most of there cars of this era. The cause of low air flow can be caused by many problems, one is shown below, and this was one of my problems in my car. Its very hard to try and trouble shoot an AC problem with the limited details posted, we really need to know both high and low side pressure readings, what the engine RPM’s were when the readings were taken, what the fan speed was while taking the readings. Most of the posts given are some common problems but will not cause high suction pressures like you are seeing but can cause low air flow. If your evaporator was plugged like mine was your suction pressure would be low unless someone not knowing what they were doing were to over charge it with Freon.

The intake for the fan when not on recirculation is on the passenger side of the car and draws air in from the lower windshield area. It’s common for debris to be drawn into the evaporator box and restrict air flow especially when the little screen is missing for a while. Cleaning this area can be a time consuming job, some times you can get to it by removing the overflow bottle and the fan motor than use a shop vac and suck out what you can get to, then use coil cleaner and a water hose to flush. You can also remove the blower motor speed resister and see what shape the down stream side to the coil is in. The best way would be to remove the coil from the engine compartment and clean it out of the car.

55 PSI is on the high side at idle for a system in good working order, but if charge correctly it could just be signs that the comp has some wear and has lost some of its pumping capacity which will show up more at low speed (idle).

My evaporator coil when removed form the car;


Hope this helps Neal

 

Thats what I was inquisitive about Neal. If there may be a mess such as that. Also what should the pressure be if 55 is too hi. No frost on the hoses btw. I will start there. I need to know its clean for starters. Also will check on a different fan for future. DB is it a C4 fan that will work???

 

system in good working order suction pressure will be around 28 to 32 psi at idle.

Neal

 

Need to have both high and low side readings to properly troubleshoot your problem.

 

if you have r12 in your system its not a bad pressure but if it was upgraded to 134a then the low pressure is a bit high as 134a needs expansion room and a low pressure of about 35 is good you should know that you have a dryer next to the condenser that has a sight glass on it if there are bubbles in it it is low

 

When I restored my 72, I found the vacuum line to the vent control was pinched during the original install and never worked.
Later, it was uncovered that MANY vettes from the late 60s to late 70s had the same problem. Apparently, the installer never checked to insure the vacuum line to the vent motor was not trapped between the assembly and the body.
You can test the door by using the hand vacuum pump to see if it opens/closes.

 

Gonna pull everything apart tonight and clean it for starters. Im sure the thing is full of crap so I will check all the other things Ive been advised of...thanks, and it is R12. And DB thanks for the email

 

You're welcome, and good luck.