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The ambient temperature differences

By Richard Hawkins, MACS Contributor

In this blog, we’re going to discuss the role of ambient temperature differences. This is the fifth in a series of blogs. You can read the preceding blogs here. Part 1, Part 2, Part 3, and Part 4.

The ambient temperature differences
photo courtesy of ToyotaUSA

Last week’s article ended with the following: 

Me:  What about the ambient temperature and humidity when the pressure problem occurred?

Technician:  About like today. Lower 90’s and about the same humidity.

Calls investigating a problem like refrigerant overcharge can get involved and lengthy and this is a good place to stop for this week. 

We will pick up where we are leaving off next week.


Me:  The refrigerant is either contaminated or it has an overcharge. Was it charged with recycled or new refrigerant?

Technician:  New.

Me:  It isn’t impossible to get some new contaminated refrigerant, but it’s unlikely especially if you are using a reputable brand.

Technician:  The cylinder is ________ refrigerant.  (I won’t get in to mentioning brands, but it was a reputable brand.)

Me:  It would be extremely unlikely for _________ to have a bad batch of refrigerant, so that makes contamination even more unlikely. Have you charged any other systems from that same cylinder?

Technician:  Yes, 3 or 4 as I recall.

Me:  Any problems with them?

Technician:  Nope, they all worked fine.

Me:  OK, let’s discuss the procedure you did when you replaced that discharge hose.  Was the engine compartment warm when you recovered the refrigerant before replacing the hose?

Technician:  No, the customer brought the car in late the previous afternoon.  We left it in the shop overnight and replaced the hose first thing the next morning. The engine wasn’t started before we replaced the hose.

Me:  Could you venture a guess on what the temperature might have been in the shop when you arrived that morning?

Technician:  Like I was saying earlier in the call, it was in the upper 60s or low 70s that morning, so the temperature in the shop was about in that range because the heat wasn’t turned on overnight. The car owner was there right when we opened and said he needed the car as soon as possible because he had to go on an unplanned trip.

Me:  OK. Please tell me about the procedure.

Technician:  I hooked up the recovery/recycling machine and recovered all of the refrigerant.

Me:  Did you remember if the pressure in the system built back up and you had to repeat the recovery process.

Technician:  I’m not 100% sure, but I don’t think so.

Me:  That’s not surprising with the vehicle temperature in the upper 60s.  Go on please.

Technician:  That hose is easy to get to, so I whipped it off of there and had the new one on probably in less than 3 minutes.  The owner was standing there watching and thought I was finished when I tightened up the second connection. He said he was going to go up and pay and would be back to get the car and hit the road. I told him it was going to be while longer as I had to pull a vacuum on the system and charge it up and performance test it. I suggested that he go up to the customer lobby and get a cup of coffee and watch the morning news on the TV while I finished.

Me:   What happened next?

Technician:  He got a cup of coffee but came straight back to the shop.  He said he had just received a call and needed to get on the road as soon as he could. He asked if I could just charge it up and not worry about testing it.  He would call me and let me know how it was working and if it wasn’t working right, he’d just turn the A/C off and bring it back the first chance he had.  I knew this customer well and knew he wasn’t going to try to throw me under the bus if a problem occurred, so I decided to accommodate him.

The vacuum pump hand been connected for probably between 5 and 10 minutes and the low side gauge was showing over 29 inches of mercury. So I disconnected it, charged the system with 24 ounces of refrigerant, did a quick leak check, turned the A/C on and it was blowing nice and cold.  I backed it out of the shop, and he jumped in, flipped me a $10.00 tip out the window and said thank you as he was leaving.

He called me about an hour or so later and said it was working fine and thanked me again.

Me:  Of course, that wasn’t the end of it, or we wouldn’t be having this conversation.

Technician:   That’s right. Two days later the customer called and said it was cooling terrible. I had him bring it back in and put the gauges on it and checked the vent temperature and it was running about 325 on the high side and about 45 on the low side and the vent temperature was about 55 as I indicated earlier.  Of course, it was in the low 90’s that day.

This image has an empty alt attribute; its file name is Picture-2.png
An ambient temperature difference as illustrated in the picture can make a significant  difference in performance and the lower temperature can mask a problem that might show up at the higher temperature.

Check back in next week and we will pick back up where we are leaving off with the conversation.

Now is a great time to make your plans for MACS 2023 Training Event and Trade Show! All the details are available here on the MACS website. I hope to see you in Nashville!

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